Petrol VS Diesel i'm confused!

[pault123]

Read an article today in local rag which stated

"A litre of diesel is now 7.49p more expensive than petrol, compared with 5.1p at the start of the year and the previous record of 5.67p in November 2006.

The AA said a diesel car, which costs on average £1,400 more than its petrol equivalent, usually takes more than 45,000 miles before the savings from greater fuel efficiency recoup the extra cost

The AA urges anyone considering the switch to a diesel car to research their motoring costs thoroughly, including start-up costs, fuel efficiency, tax disc band, annual mileage - and leeway in their calculations for petrol-diesel price changes."


I'm looking at swapping my 1.4l Petrol car for 1.9l Diesel car.

It is a straight swap with a trader and road tax, insurance costs no more. So the only difference will be my fuel spend.

My Petrol car does 30 mpg combined.

The Diesel 55 mpg combined (64mpg on extra urban!)

Am I missing something but why shouldn't I get a diesel? I do about 12,000 miles a year. (i know diesel costs more per litre but 25 mpg easily offsets this)

[vikingaero]

The figure for the diesel cars mpg sounds like it's been taken from a brochure. I find that deducting 5mpg from a petrol cars quoted mpg is about right and taking off 8-10 mpg from the quoted figures for a diesel.

Diesel prices are high at the moment because each barrel of oil can only be refined into certain quantities of each type of fuel. Because it is winter, diesel fuel costs a lot more than in the summer because of competition with heating oil.

[deltic]

How much cheaper is a petrol equivalent of the same car you are buying ?

The diesel car is only cheaper to run if the price differential versus an equivalent petrol plus the extra finance charges for this differential (if applicable) is less than the fuel saving over the period of ownership.

This assumes tax bands, servicing costs, and depreciation are the same.

[Conor]

The AA are talking crap. I'm saving £25 a week based on 300 miles. So that's 56 weeks (£1400) at 300 miles per week which is 18,000 miles. The diesel will also have lower servicing costs, lower insurance costs and a higher resale value.

I'm getting an average of 57MPG from a 2L Mondeo TDCi.

[pault123]

I figured winter fuel could effect it.

The car is approx £2500 value. Ive seen Petrol equiv for about £2000-£2200.

One of the main reasons for the swap is current spend on Petrol is getting ridiculous.
I suppose the question i'm asking is tax, insurance and initial outlay is £0 difference.

Is there some kind of minimum milage to do in a diesel per week to get the mpg into the extra urban mode and hence reap the savings? (this isn't the first time i've read unless doing a certain milage per year don't buy a diesel)

Conor if I could save £50 to £100 a month I would be happy :)

[deltic]

Well i make it that you'll be approx £800 per annum better off in fuel at 55mpg and about £580 per annum better off even at 45mpg - I think that gives you yr answer.

[Conor]

Is there some kind of minimum milage to do in a diesel per week to get the mpg into the extra urban mode and hence reap the savings? (this isn't the first time i've read unless doing a certain milage per year don't buy a diesel)


I don't know where you've heard that rubbish. In fact, because a diesel doesn't need to use "cold start" or "choke" for the first few miles as a petrol engine does, you get the same economy from the first turn of the wheel as you do throughout the rest of the day.

[Altarf]

The fuel economy figures quoted by manufacturers for 'urban', 'extra-urban' and 'combined' are based on a set EU testing program and have no relationship with reality.

To give you some examples -

The cold start part of the test is carried out with the vehicle having being kept at an ambient temperature of between 20c and 30c for several hours. So the test is only representative of use in the UK on a warm summer afternoon, and certainly never reflects the use of a car when you set off on a winter morning.

The 'urban' part of the test is 2.5 miles, with an average speed of 12 mph and at no time does the speed exceed 31 mph. The 'extra-urban' test immediately follows on and is only an extra 4.3 miles, with an average speed of 39 mph. The 'combined' is just an average of the 'urban' and 'extra-urban'. So the whole test is less than 7 miles.

During the 'extra-urban' part of the test the car is accelerated to 75 mph once, but only stays at that speed for a few seconds. The test does not replicate long distance cruising at 60 to 80 mph that you would do on A roads or motorways.

There are no racing starts or any sort of fast acceleration, as the same test is used whether it is a Ferrari or a micro-car being tested. So the time allowed to accelerate has to be something that the slowest car being tested can cope with. Therefore the time allowed to accelerate from 0 to 62 mph in the 'extra-urban' part of the test is 50 seconds, which is of course what all the cars do to get the best mpg.

So there is no point at all in looking at the figures and thinking you could get the mpg figures quoted, all they are useful for is comparing one car to another, and only in the rough 'this one uses more fuel than that one' way.

[Conor]

The fuel economy figures quoted by manufacturers for 'urban', 'extra-urban' and 'combined' are based on a set EU testing program and have no relationship with reality.


Indeed. I beat them with frightening regularity and I'm no Miss Daisy by any stretch.

[cyclonebri1]

I agree with Conor,:money: , almost on this one. The reported extra maintenance costs for a diesel are unfounded. They need cost no more to maintain and as they get a little older, little more to purchase.
They do however use a programmed enrichment system on cold start and just like a petrol engined car are much less economical on start up than when fully warmed up, but no more or less so than the petrol engined alternative, ie, It's all proportional and since the diesel will do at least 40 and at best about 80% more mpg, well, it's a no brainer.;)

[Wig]

Well you really shouldn't be comparing the diesel mpg to your old car (the one you are about to sell) You should be comparing it to the 'petrol equivalent car' of the 'diesel car' you are thinking of buying.

Fiat Punto 1.2 16v petrol can easily return 43 mpg all day long. There are probably other equally frugal petrol cars available.

[pault123]

Well you really shouldn't be comparing the diesel mpg to your old car (the one you are about to sell) You should be comparing it to the 'petrol equivalent car' of the 'diesel car' you are thinking of buying.

Fiat Punto 1.2 16v petrol can easily return 43 mpg all day long. There are probably other equally frugal petrol cars available.

Hi Wig,

Looking through all the petrol models the best mpg I can find is 34. I could save myself £200-£400 initially if I went for a Petrol model.

So the diesel I think is still looking preferable. :money:

[pault123]

The 'urban' part of the test is 2.5 miles, with an average speed of 12 mph and at no time does the speed exceed 31 mph. The 'extra-urban' test immediately follows on and is only an extra 4.3 miles, with an average speed of 39 mph. The 'combined' is just an average of the 'urban' and 'extra-urban'. So the whole test is less than 7 miles.


The stated extra urban figure is 64 mpg, if I can get that after 2.5 miles @ an average speed of 39mph, motorway cruising mpg of 55mpg hopefully should be achievable :beer:

(its a VW engine based on the 1.9 TDI 90bhp year 2000 i think)

[Altarf]

I think that you may be disappointed because you are not comparing like for like.

You are comparing the actual mpg you are achieving in your current car, with the theoretical mpg that is possible to achieve under lab conditions.

You say that your current 1.4l car achieves 30 mpg and you are planning on buying a 1.9l VW based diesel that achieves 64 mpg. To take an example, if you compare a 1.4l petrol VW Golf with a 1.9l diesel Golf you will see that the extra-urban figure for the petrol is 51.4 against 65.7 for the diesel, so only a 15 mpg difference. The same difference applies to the urban or average mileage. Now neither car is actually going to achieve these figures, but you could expect the difference between them to be a reasonable indicator.

So at the current 7p per litre price difference between petrol and diesel, driving 12000 miles you would save perhaps £200 per year. However given that diesel cars are more expensive to buy than petrol cars, you may no actually see this saving.

You say that you are doing a straight swap with a dealer, petrol for diesel. Unless you have found a very generous dealer, I assume that the diesel is an older or inferior car to what you are swapping, so there is going to be a cost to change that you should factor in to your calculations, and then see whether the £200 fuel saving is worth it.

[mitchaa]

Petrol vs Diesel

MK4 1.8T 150bhp Golf Gti (Petrol)
Mk4 1.9T 150bhp Golf TDI (Diesel)

Both cars near enough identical, however the TD car costing £2000 more at purchase price than its petrol equivelant.

The petrol should average 35-40mpg (Lets take 37 mpg)
The diesel should average 50-55mpg (Lets take 52 mpg)

The average annual mileage = 12000 miles,

TDI you would have to buy (12000/52= 230.77 gallons of diesel)
Petrol you would have to buy (12000/37 = 324.32 gallons of petrol)

1 gallon of fuel = 4.54litres

TDI you would buy (230.77 x 4.54) = 1047.7 litres of diesel
Petrol you would buy (324.32 x 4.54) = 1472.4 litres of petrol

According to this site .... http://www.petrolprices.com/

The average cost of a litre of petrol in the uk at the moment is 106.9p
The average cost of a litre of diesel in the uk at the moment is 114.8p

The cost of fuel per year for the diesel = (1047.7 x 1.148) = £1202.76
The cost of fuel per year for the petrol = (1472.4 x 1.069) = £1573.99

A difference of £371.23 per year

Now considering the TDI car originally cost £2000 more to purchase it would take at todays fuel rates about 5 1/2 yrs to break even.

So yes the AA do have a valid point, diesel isn't neccessarly the best option

Additionaly, you can easily opt for a small engined petrol car (Clio 1.2) that will return 55mpg and the fuel costs would actually work in favour for the petrol

[pault123]

Thanks Altarf and Mitchaa, certainly valid points.The official "theoretical mpg that is possible to achieve under lab conditions." combined figure for my current car is 40mpg, in actuality I get 30mpg.

I think i'm probably putting too much faith on the 55mpg figure quoted for the diesel as being what I will get :o (althought Conors " I'm getting an average of 57MPG from a 2L Mondeo TDCi." has spurred me to research some real figures being achieved by 1.9 Tdi VW drivers of the same car/model)

Paul - also off to look at some Petrol alternatives with the possibility of :money:

[smoky joe]

Thanks Altarf and Mitchaa, certainly valid points.The official "theoretical mpg that is possible to achieve under lab conditions." combined figure for my current car is 40mpg, in actuality I get 30mpg.

I think i'm probably putting too much faith on the 55mpg figure quoted for the diesel as being what I will get :o (althought Conors " I'm getting an average of 57MPG from a 2L Mondeo TDCi." has spurred me to research some real figures being achieved by 1.9 Tdi VW drivers of the same car/model)

Paul - also off to look at some Petrol alternatives with the possibility of :money:


well i have had a 2001 passat for 3 years which the computer regularly tells me i get 53mpg around the doors and a 3 hour motorway drive 64mpg at 55 to 80 mph now i regularlly check the computer figures between fill ups and they do overestimate a tad but it is still allways above 50mpg which is excellent being its a big heavy car oh and its only £120 yearly tax ;)

[cyclonebri1]

well i have had a 2001 passat for 3 years which the computer regularly tells me i get 53mpg around the doors and a 3 hour motorway drive 64mpg at 55 to 80 mph now i regularlly check the computer figures between fill ups and they do overestimate a tad but it is still allways above 50mpg which is excellent being its a big heavy car oh and its only £120 yearly tax ;)


I can second the figures for the passat 1.9tdi I was loaned for a week to cover commuting to a training course, A38/Walsall/Wolverhampton so fairly mixed conditions given rush hour and Jan weather. Over 400+ miles it averaged 52mpg and I wasnt exactly hanging about.

[greenman7]

Diesel engines get better fuel economy simply because they do not need to burn as much fuel as a petrol engine to get the same power. Diesel engines are also built heavier than a petrol engine to sustain the added stress of the higher compression ratio. Diesel engines do not have an ignition system so you will never have to tune them up. Exhaust systems last longer because diesel fuel exhaust is not as corrosive a petrol engine exhaust.

With lower depreciation, lower maintenance costs, higher mpg, less CO2 emmissions, same insurance costs diesel must be the way to go.

[pault123]

I can second the figures for the passat 1.9tdi I was loaned for a week to cover commuting to a training course, A38/Walsall/Wolverhampton so fairly mixed conditions given rush hour and Jan weather. Over 400+ miles it averaged 52mpg and I wasnt exactly hanging about.

Its actually a Passat i'm looking at :money:

[thescouselander]

Diesel engines get better fuel economy simply because they do not need to burn as much fuel as a petrol engine to get the same power. Diesel engines are also built heavier than a petrol engine to sustain the added stress of the higher compression ratio. Diesel engines do not have an ignition system so you will never have to tune them up. Exhaust systems last longer because diesel fuel exhaust is not as corrosive a petrol engine exhaust.

With lower depreciation, lower maintenance costs, higher mpg, less CO2 emmissions, same insurance costs diesel must be the way to go.

I'm not sure the maintenance costs are actually lower. Maybe in the old days but diesel engines are now more complicated. On the BMW forum I frequent it is the diesel drivers who are spending a fortune on replacing turbo chargers and leaking high pressure injectors. Be warned, these are expensive parts and the same problems are found on other makes too.

Also, with regard to emissions, although diesel has lower CO2 emissions it is far worse than petrol in respect of the other emissions put out - especially particulates that have been linked to a number of serious illnesses.

[goldspanners]

older diesel engine fuel injectors and pumps could be got relatively cheap compared to new high pressure pumps and injectors,you could buy a full set of old injectors for the price of just 1 new cdi type.
i have a 110 cdi vito for work,2 of the injectors are easy to replace,the other 2 are a complete nightmare,the engine has to come out to do this,between parts and labour costs the van will be scrap when these parts fail. it is a common ocurance on these vehicles.
as the scouser said above when modern diesels go wrong they usually do it in style,costing you a fortune.but when they dont they are great.

[pault123]

The model i've been offered is the 110 bhp common rail I think its reffered to, there looks to be an improved Pump Duse version 115bhp brought out in 2001 which uses far higher pressure - I suppose the PD could be a bad thing in repair terms then.

[goldspanners]

The model i've been offered is the 110 bhp common rail I think its reffered to, there looks to be an improved Pump Duse version 115bhp brought out in 2001 which uses far higher pressure - I suppose the PD could be a bad thing in repair terms then.

it could be,but i very much doubt all 4 injectors will go down at the same time,with the right equiptment it is easy to diagnose which injector it is that is failing.
it seems a few manufacturers are going back to using the common rail system.

[chuckles1066]

(althought Conors " I'm getting an average of 57MPG from a 2L Mondeo TDCi." has spurred me to research some real figures being achieved by 1.9 Tdi VW drivers of the same car/model)

My Focus CC has the same 2.0TD engine as Conor's, mine's married to a six-speed gearbox, I don't know about his. I only use Shell V-Power diesel together with a dash of Millers fuel additive.

I get 47mpg but I do a lot of motorway driving at 90mph+..........if he's getting 57mpg, then he must be driving like a vicar's wife.

[cyclonebri1]

Quote;
I get 47mpg but I do a lot of motorway driving at 90mph+..........if he's getting 57mpg, then he must be driving like a vicar's wife.

No you don't,;) you drive at 70mph. Which is why Coner gets 57mpg;);) ;) ;) ;)

Most diesel will give figures like this at a constant 65-70mpg

[harveybobbles]

While were on the subject of mpg etc, could I just point out that it REAAAAAAAAALLLLLY annoys me when I get customers in looking at cars with 3.0 litre or higher petrol engines and then ask what the fuel consumption will be while out on test drive.
I feel like saying "Why buy a 3.0 if you're bothered if you get 28mpg or 31..."

Or when they drive like a tvvat on a test drive and ask what the mpg is.

"not much if you continue to drive like a !!!!!..."

[MORPH3US]

OP, if fuel consumption is what bothers you most in a car, do you really need a Passat sized car?

If you could stump for a smaller car then you could a) get the car cheaper (or get a newer / better model), b) get even better mpg, c) possibly get into £35 tax bracket etc...

Just a thought.

[loofer]

The model i've been offered is the 110 bhp common rail I think its reffered to, there looks to be an improved Pump Duse version 115bhp brought out in 2001 which uses far higher pressure - I suppose the PD could be a bad thing in repair terms then.

The unit injector's on the PD are no more likely to fail than on the common rail VE (110hp) engines. The cost to replace unit injectors, however, will be more.

The plus point with the 115 PD is more power (i'm not talking boy racer mode) which is helpful for in gear acceleration on motorways. The engine also comes mated with 6 speed gearbox so all in all it is very economical. I tend to get 60+mpg out of mine. Thats a 35 mile motorway trip.

The not-so-plus point is that the PD engines require 'special' Oil. It can't be just any full synthetic oil. We're talking £40+ for just a 4-5 litre bottle in some cases. Can get non branded for about £25. Using incorrect oil can damage engine internals. Has to meet VW spec.

Don't forget though... if you buy a PD then it's likely it will be registered 2001 or after. Road tax will be cheaper.
I have just paid £120 for 12 months on my PD 115.
Pre-2001 cars are based on engine size so you're looking at about £165+ for 12 months

[thescouselander]

While were on the subject of mpg etc, could I just point out that it REAAAAAAAAALLLLLY annoys me when I get customers in looking at cars with 3.0 litre or higher petrol engines and then ask what the fuel consumption will be while out on test drive.
I feel like saying "Why buy a 3.0 if you're bothered if you get 28mpg or 31..."

Or when they drive like a tvvat on a test drive and ask what the mpg is.

"not much if you continue to drive like a !!!!!..."

I don't think this is an unreasonable question. Not all cars are equal so if the customer wants to compare two different but similar cars they may be interested in the difference in fuel consumption even though in both cases the fuel consumption will be relatively high.

[pault123]

Some fantastic advice here :beer:


I tend to get 60+mpg out of mine. Thats a 35 mile motorway trip.



Another confirmation of good mpg from this engine. :) It sounds like swings and roundabouts as to 110 vs 115 PD - saving of £60ish a year on roadtax but higher oil cost.


OP, if fuel consumption is what bothers you most in a car, do you really need a Passat sized car?

If you could stump for a smaller car then you could a) get the car cheaper (or get a newer / better model), b) get even better mpg, c) possibly get into £35 tax bracket etc...

Just a thought.


Hi Morph3us,

Its for lugging bikes around @ weekends, and lots of big electrical goods in the week. I need a very long load length hence an estate offers more of this than some vans, offers it seems a real achievable 50-60 mpg - only downfall is the roadtax :o

[Pew Pew Pew Lasers!]

The not-so-plus point is that the PD engines require 'special' Oil. It can't be just any full synthetic oil.


Its only low-ash oil, you can buy Mobil-1 to that spec for £20+vat for 4 litres from Costco.

[td]

Hi all,

I am playing these arguments over too. We are just looking to buy a family car a bit bigger than the megane we have now (51 reg) and so we have been looking at

Skoda Roomster
Citroen Xsara Picasso
Renault Scenic

We are quite pollution conscious but don't really understand the technicalities about petrol-v- diesel pollution debates and we have therefore considered diesel options as we presumed that because they were lower tax bands that they would be lower polluters. Is this not the case?

We generally drive around the city we live in and don't go on motorway that much except for holidays weekends etc.

We generally keep our cars 7 years or more because I hate buying cars as I can never decide what to buy. We were looking at the Zafira mainly because our garage has a diagnositc machine for it and it costs a fortune to take cars to dealers machines but the zafira isn't great on emissions so we were put off.

There are pretty good deals on diesel and petrol versions of all 3 cars we've looked at. AAaaargh I hate buying cars.

Any thoughts on these cars would be appreciated too.

ta

td

[Pew Pew Pew Lasers!]

From that list I'd go with the Roomster. I'd rather eat my face than own a French car. However, if you're pollution conscious then buying a new car is quite perverse, the energy cost of building a new car is significant.

Diesels are superior in almost every respect regarding emissions from the exhaust. The real 'green' route to running a car is to keep it until it must be put on the scrap heap. That means regular maintenance and mechanical sympathy.

[cyclonebri1]

From that list I'd go with the Roomster. I'd rather eat my face than own a French car. However, if you're pollution conscious then buying a new car is quite perverse, the energy cost of building a new car is significant.

Diesels are superior in almost every respect regarding emissions from the exhaust. The real 'green' route to running a car is to keep it until it must be put on the scrap heap. That means regular maintenance and mechanical sympathy.

TD, if you have 51 megane it'll be the mk 1? I had one of these 10 months old and hated it, keeping it only 4 weeks. You must like french cars as you're considering another. I did the same, I bought the newer megane diesel estate as my latest car at a year old a year ago. What a difference. I tend to keep my cars for around 6 to 8 years. I wasn't convinced the 2st one was built well enough to go the distance, the latest megane is much improoved, scenic is better looking though.

Daughter recently bought a scenic although the latest zafira was the car of choice but too expensive:confused:

[jeepjunkie]

My 2004 TDI 130 Passat Sport will do the low 50s mpg on a run, not bad for a big car with loads of room and plenty of grunt...

[LandyAndy]

I had an 'x' reg Golf tdi 90 bhp as a company car and it refused to do anything other than 60 mpg regardless of conditions. I replaced it with a '53' reg Golf GTi 150bhp diesel and that refused to anything other than 58mpg.

[pault123]

I had an 'x' reg Golf tdi 90 bhp as a company car and it refused to do anything other than 60 mpg regardless of conditions. I replaced it with a '53' reg Golf GTi 150bhp diesel and that refused to anything other than 58mpg.

I bet you didn't complain about that! ;)

[drewwa]

I have two 1.9 TDI cars. A mk1 Audi A4 and a Mk5 Passat, both with the 115 TDI PD varient, year 2000.

I have had the Audi 'chip tuned' which gives it 160bhp, rather than the standard 115.

The Audi is a commuting car, bought for long distance running, quietness, economy, reasonable performance and fitting in with the company car park.

http://www.vwgolfmk1.org.uk/modules/coppermine/albums/userpics/forweb.JPG

The Passat is the family wagon, Estate. Designed for shopping, towing a trailer tent, two kids and a dog.

Both cars return an average of just over 50mpg on motorway runs, and around mid 40s in town. I'm disappointed if I don't get 600 miles on a full tank.

Both purchased at 2 years old. Audi - £10k(£22k new), Passat £9k(£18k new).

Both have been regularly serviced with our Audi main dealer and retain FSH.

The Audi has covered 145k miles, and the Passat around 75k. Repairs and servicing over six years have cost about £3000 for the Audi, and £2400 for the Passat (Audi lost the airbag and dashboard computer - v. expensive)

I anticipate keeping both cars until the mortgage is paid in 6 years (I hope!). By this point the Audi should have near 300k miles and the Passat approaching 150k.

Both cars are extremely resilient and tough, look pretty much as they did when they were new and show no signs of needing imminent replacement.

Notable repairs to date:

Audi
Dashboard and airbag computer (no dials and no airbag on collision!)
Temperature sensor (bad starting, poor economy)
Rear disc brakes replaced
Exhaust replaced due to internal corrosion

Passat
Temperature sensor replaced (bad starting, poor economy)
Interior lights failed

Cheers,

Drew.

[thescouselander]

From that list I'd go with the Roomster. I'd rather eat my face than own a French car. However, if you're pollution conscious then buying a new car is quite perverse, the energy cost of building a new car is significant.

Diesels are superior in almost every respect regarding emissions from the exhaust. The real 'green' route to running a car is to keep it until it must be put on the scrap heap. That means regular maintenance and mechanical sympathy.


Total nonsense I'm afraid, diesels are better with regard to CO2 emissions but they pump out more Nitrous Oxides and more worryingly large quantities of particulates that have been linked to a number of serious health conditions.

[Pew Pew Pew Lasers!]

I suggest you do some research on this, the matter isn't nearly so black and white. For instance, petrol also produces particulate emissions that are much smaller than PM10s, and therefore more easily absorbed into the body. Petrol produces far more carbon monoxide and more hydrocarbons than equivalent diesel engines.

The nitrous oxide levels of diesels are only slightly higher than catalysed petrol engines.

[eslick]

We are on to our second diesel and to be honest I wont go back, 500+ miles to the tank around town and 60+ miles to the gallon on a motorways. Just dont go for a small engine one, or you will probably wish you had a petrol one especially when you pull away at round abouts or junctions.

[thescouselander]

I suggest you do some research on this, the matter isn't nearly so black and white. For instance, petrol also produces particulate emissions that are much smaller than PM10s, and therefore more easily absorbed into the body. Petrol produces far more carbon monoxide and more hydrocarbons than equivalent diesel engines.

The nitrous oxide levels of diesels are only slightly higher than catalysed petrol engines.

I have researched this area but don't believe me check out these graphs from the DOT.

http://www.dft.gov.uk/pgr/roads/environment/research/cqvcf/emissionsfactorsforeuroiiicars?page=11

If we compare a large petrol engine with a large diesel engine at a cruising speed of around 50 kmh we can clearly see that the NOx emissions for the Diesel car are a factor of 10 higher than the petrol car (hardly a small difference).

Also particle emissions are much higher for the diesel car (again by an order of magnitude).

Thats for Euro III emissions engines anyway - things should improve somewhat with the newer IV and V standards.

[Pew Pew Pew Lasers!]

You'll forgive me if I don't rely on graphs based purely on engine sizes, and that don't even specify the exact engine size or technologies used (turbo, common rail, etc). I am unclear as to whether they are comparing engines with catalysers or not - my diesel engine certainly has a catalyser.

Also, it is not the speed of the vehicle that matters - it is the distance covered with fuel consumed that is important.

[thescouselander]

You'll forgive me if I don't rely on graphs based purely on engine sizes, and that don't even specify the exact engine size or technologies used (turbo, common rail, etc). I am unclear as to whether they are comparing engines with catalysers or not - my diesel engine certainly has a catalyser.

Also, it is not the speed of the vehicle that matters - it is the distance covered with fuel consumed that is important.


Yes but the graphs clearly show that the emissions for NOx and PM per km are higher for diesel over all speeds. If you download the PDF report that explains how the results were put together. The data was collected was from a number of vehicles which were catagorised into the small medium or large range. The list of cars it given at the end of the report.

There is no doubt that Diesel cars are worse for PM and NOx emissions.

[chuckles1066]

We are on to our second diesel and to be honest I wont go back, 500+ miles to the tank around town and 60+ miles to the gallon on a motorways. Just dont go for a small engine one, or you will probably wish you had a petrol one especially when you pull away at round abouts or junctions.

Totally agree.

Taking a Ford Puma 1.7 petrol across to Adenkerke on a booze/ciggie daytrip (506 mile round trip) involved stopping in Calais for more petrol and then filling up again as soon as we'd got home.

Our Focus CC 2.0TD did the entire trip on a full tank (fuel warning light illuminated about 4 miles from home).

[Pew Pew Pew Lasers!]

Yes but the graphs clearly show that the emissions for NOx and PM per km are higher for diesel over all speeds. If you download the PDF report that explains how the results were put together. The data was collected was from a number of vehicles which were catagorised into the small medium or large range. The list of cars it given at the end of the report.

There is no doubt that Diesel cars are worse for PM and NOx emissions.

You should distinguish between what kinds of PMs are being emitted. You should also bear in mind that without catalytic converters the figures are very much worse for petrol engines.

Also consider that catalytic converters do not operate fully until they are hot. Most car journies are very short and barely allow enough time for the cat to get up to temperature. I very much doubt the above graphs demonstrate this.

[thescouselander]

You should distinguish between what kinds of PMs are being emitted. You should also bear in mind that without catalytic converters the figures are very much worse for petrol engines.

What would be the point in this? All new cars sold in the UK do have catalytic converters and this has been the case since 1992. The correct functioning of this equipment is tested during the MOT. Testing a car with the catalytic converter removed would not be a representitive test.



Also consider that catalytic converters do not operate fully until they are hot. Most car journies are very short and barely allow enough time for the cat to get up to temperature. I very much doubt the above graphs demonstrate this.


With regard to the warmup time for catalytic converters, on more recent cars manufacturers have taken steps to improve the situation. For example, my car has extra catalytic converters near the exhaust manifold that heat up much quicker than the main cat. Typically the catalytic converter, even on cars manufactured some years ago, can reach operating temperature in under 30 seconds.

In any case, most miles are done with the engine at full temperature.

[Pew Pew Pew Lasers!]

....and how do you think those cats are heated up - with fresh air?

Compare fuel consumption on startup with fuel consumption at normal operating temperature. I think you'll find theres a very significant difference.

Average journey length in the UK for commuting is somewhere around 6-8 miles. A modern car even at 40mph will take around 2 miles to achieve full operating temperature. The tests you linked to did not include warm-up cycle and do not include (it would be impossible to IMO) the variety of driving conditions in the UK.

I don't disagree with everything you say but to describe what I posted as "nonsense" is something I take exception to. Modern diesel engines are very far removed from the common stereotypical view of their cleanliness.

[thescouselander]

....and how do you think those cats are heated up - with fresh air?

Compare fuel consumption on startup with fuel consumption at normal operating temperature. I think you'll find theres a very significant difference.

Average journey length in the UK for commuting is somewhere around 6-8 miles. A modern car even at 40mph will take around 2 miles to achieve full operating temperature. The tests you linked to did not include warm-up cycle and do not include (it would be impossible to IMO) the variety of driving conditions in the UK.

I don't disagree with everything you say but to describe what I posted as "nonsense" is something I take exception to. Modern diesel engines are very far removed from the common stereotypical view of their cleanliness.


Perhaps on reflection my use of the term "nonsense" was a little strong so I appolgise for that.

I mearly wanted to to demonstrate that Diesel is not as environmentally friendly as is sometimes claimed based purely on CO2 emissions. There are pros and cons with each fuel type.

I personaly have a problem with particulate emissions from Diesel vehicles as they effect my nose in a similar way to hay fever (lots of sneazing and very runny). This caused me a lot of problems until I bought a car with a pollen filter. I have to say though, the worst offenders were busses and not cars - moden diesels seem to be very good but you sometimes see the odd smokey one especially if it is being driven fast.

[Pew Pew Pew Lasers!]

I have it on good authority that catalytic converters on buses are often removed in-between emissions testing, to increase mpg.

Looking at some of them, I can well believe it.

[pault123]

Passat
Temperature sensor replaced (bad starting, poor economy)
Interior lights failed

Cheers,

Drew.

Drew can you elaborate on the temp sensor replacement?

I now have the Passat and very impressed with its performance and frugalness!On a full tank up to now ive done 250 miles, still with 75% fuel left and an estimation of 340 miles left in the tank :money:


BUT it does have an issue where the engine temp on the dash drops to the far left of the dial at random, I wonder if this is purely driver information or if this temp sensor actually controls other parts of the vehicle?

[Pew Pew Pew Lasers!]

The temperature sensor is very important. Does your needle drop instantly, or slowly (over a period of minutes)?

[pault123]

The temperature sensor is very important. Does your needle drop instantly, or slowly (over a period of minutes)?

Strangly enough its only done it over a space of 2 days earlier last week. Once it reaches middle of the dial which is normal operating temp, it slowly starts to fall and stays on the far left like the engines cold.

Once I restart it after a short stop it goes straight up to the middle.

I'm thinking its a loose connection somewhere?

[Pew Pew Pew Lasers!]

Does the heating work throughout, when it does this?

[pault123]

Its got air conditioning so i'm not sure how I would test this?

There is an ECON button which may use engine heat?

[Pew Pew Pew Lasers!]

Air conditioning can be on when the temperature is fully on. What I mean is, when the temperature sensor reads 0, do you still get plenty of heat from the vents, or does it struggle to keep you warm?

[pault123]

Air conditioning can be on when the temperature is fully on. What I mean is, when the temperature sensor reads 0, do you still get plenty of heat from the vents, or does it struggle to keep you warm?

Yes still very toasty :j

[Pew Pew Pew Lasers!]

Then at least coolant is circulating. I suggest you investigate replacing the temperature sender, I don't know where it will be but a model-specific forum for your car will get an answer.

[drewwa]

Paul,

This might all be old news by now - sorry, missed the thread!!

The temperature sensor going bad caused the following on both our Audi and Passat

1. Occasional rough starting (sounding like running on 3 cylinders)
2. Idle high (2500rpm at startup!) for 10 seconds and then normal
3. 5mpg-ish drop in fuel economy
4. Smoke on startup
5. Temperature gauge on dashboard dropped to zero, returned, dropped to zero for a while and finally stopped working all together.

Replaced the sensor (about £30 + labour as I recall) on both cars. Both cars transformed - definitely worth doing. All problems went away. It also cured an intermittent problem on my Audi where the ECU would go into 'limp home' mode on heavy acceleration (ahem :wink:)

Cheers,

Drew.

[pault123]

Paul,

This might all be old news by now - sorry, missed the thread!!

The temperature sensor going bad caused the following on both our Audi and Passat

1. Occasional rough starting (sounding like running on 3 cylinders)
2. Idle high (2500rpm at startup!) for 10 seconds and then normal
3. 5mpg-ish drop in fuel economy
4. Smoke on startup
5. Temperature gauge on dashboard dropped to zero, returned, dropped to zero for a while and finally stopped working all together.

Replaced the sensor (about £30 + labour as I recall) on both cars. Both cars transformed - definitely worth doing. All problems went away. It also cured an intermittent problem on my Audi where the ECU would go into 'limp home' mode on heavy acceleration (ahem :wink:)

Cheers,

Drew.


Thanks for help guys replaced the temp sender cost £20 fitted. Works a treat now, and better performance to boot.

In terms of the OP and my question on petrol vs diesel, i'm getting on average 600 miles per tank with the diesel, my petrol used to average 325. But my fuel bill certainly isn't double an extra £15 -approx which for double the milage is a ridiculous testament as to the benefits of Diesel! :beer: