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_2

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_3

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_2

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_3

pault123 wrote: »

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_3

Altarf wrote: »

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.