Running a diesel car

flamin_galah

I'm looking to buy a new (secondhand) car and I was thinking of going for diesel as I like the eco type cars that have high MPGs and low tax. I have been told that not doing regular long runs will damage a diesel engine. I'd be doing roughly 9000 miles a year. Most of these would be around town and between local towns. Journeys of 10-15 minutes at up to 60mph but mostly around the 30mph mark. Every 1-2 weeks I'd be doing a motorway journey of around 20 mins, plus the return journey. Roughly 5-6 times a year I'd be doing long motorway journeys of 4+ hours plus return.

I've outlined all this because I don't know if this sort of driving pattern is good for a diesel engine. One of the reasons I'm suss is because one of the people who told me was a car salesman who said that the difference in MPG between the petrol and diesel options that I was looking at wasn't enough to justify getting a diesel. However, the petrol car had an urban MPG of 39 and the diesel one had an MPG of 53, which to my calculations still seemed a significant saving. He was quite flippant, saying it would only be around £30 a month more in fuel costs but that's quite high to me as I was thinking of £50-60 a month for my fuel budget. Especially when the petrol one also had a tax band of £110 when the diesel was £30.

The second person who told me about this diesel running thing said it only applies to new cars which need a good run in, not secondhand ones. I'd be buying roughly a 4 year old car.

Are diesel cars really that bad as run arounds? I don't want to be building up potentially expensive repair problems but the MPGs of some of the diesel cars look great. I know that the advertised MPG isn't always accurate, but I am using them as a guide to compare between cars, not taking them as the absolute value that I will get out of a car.

mcpitman

I believe the break even point on petrol vs diesel is about 15k miles.

So you need to be doing 15k+ miles to outweigh the (normal) higher cost of fuel and servicing and make a diesel car viable (under 15k=petrol).
I say normal cost of fuel, because parts of the country diesel is very close to or even slightly cheaper then petrol right now.

Modern diesels (with dpf's fitted) tend not to like "town" driving, they do need good regular runs to get then fully warmed through and allow the dpf to clear itself.

In your situation I would be looking for a petrol/hybrid car, I have a diesel but do in excess of 30k miles per year, mainly at motorway speeds.

Guys_Dad

Yes diesel cars cost more than their petrol equivalent but the 15k per annum mileage fails to take into account the additional amount you get back when you sell it on.

I have run diesel cars in mixed town/country doing between 10-12k p.a. for years. Never had any DPF problems. I like the low revving engines, obviously fuel consumption.

I would go for an automatic (avoids dual mass flywheel problems), use Shell V-plus on every 3rd tankfull (or every one if you like!) and get the best deal you can on purchase .

jimjames

in mixed driving my Passat diesel gets around 45mpg, sometimes lower. My Puma petrol gets 40mpg, modern petrol cars should be much higher.


So it really is only worthwhile changing to diesel if you are doing huge mileages as you're unlikely to save much on fuel to cover the cost of the new car.

worried_jim

I think a four year old car will definitely have a dpf fitted. I would say you are borderline diesel. You say about eco cars- diesel is a killer in towns due to high nitrogen dioxide emissions and is likely to be legislated against in the near future-

http://www.telegraph.co.uk/motoring/news/11007326/Diesel-car-drivers-betrayed-as-EU-cracks-down-on-Britain-over-air-pollution.html

I would be looking at petrol hybrids all the way.

flamin_galah

I compared the average MPGs of two cars that I've looked at - one petrol and one diesel in a calculator online and it said that on 9000 a year I'd save £250/year on fuel costs. That was with me putting 115.9p for petrol and 120.9p for diesel as I assume the current low diesel prices won't stick. So that would suggest that diesel is still cheaper to run even at 9k miles a year. Mcpitman, are diesel services more expensive?

It was this long run thing that was my main issue, I wondered if my occasional longer driving would be enough to cover it - I think it's a filter issue, I think that's what the salesman said.

Guysdad, why would you recommend occasionally filling up with Shell V-plus, what benefit does it have?

Jimjames, the petrol cars I've been looking at have an advertised MPG of around 40 urban and 50 average, so not as high as you might think. Still better than the useless tank I am currently driving which has an advertised MPG of 26 urban which I think I am lucky if I hit these days!

Thanks for the tips folks, I hate car buying so much, any advice is welcome!

flamin_galah

I've just looked at hybrids and for the age I'm interested in they're a bit expensive! They start at £8k and I'm looking more in the range of £5-7k but thanks for the suggestion.

getmore4less

Is the cost of running a car that much difference at these mileages.

Add up the fixed costs and depreciation whats that per mile over say 10k

In my view

If you like the diesel experience(coupled to a DSG it is great for your sort of trips) go for it.

A couple of hundred here or their a year makes little difference.

Rather than newish go for a well looked after older(pre dpf) model with decent spec and you can't go wrong.
save so much up front it won't matter.


The real killer for consumption for a diesel is the very short trips where the thing does not warm up.

Your mix of trips looks ok for a DPF anyway.


If you have a car that works you will save more just keeping that in good running order until it starts to cost.

What sort of vehicle are you looking at.

lazer

I ad a 2007 polo 1.2L petrol which i then replaced with a 2007 1.4L TDI Polo - so very similar car.

I do a mix of Motorway driving, town driving and rural roads driving, my commute miles are 12k a year and probably another 3k please miles a year. Changing to Diesel is the best thing i have ever done.

A full tank of fuel does 550 mile minimum in the petrol car it was 350 maximum. I did work out the Mpg at one stage and the petrol was about 35mpg and the deisel about 60mpg. This is combined with the £100 a year tax savings.

The saving in running costs definately outweighs the increase cost of service etc (The tax saving alone pays for any slight increase!).

The extra cost is the cost of purchase, but well it cost me £500 to change cars (and the new one is 6 months younger) and i have already saved more than that.

If buying new, it would take 15k miles a year to make it worthwhile, if buying secondhand there is minimal difference in some cars.

Also a deisel engine is likel to outlast a petrol engine - the petrol car i had had 90,000 miles on it, the deisel about the same, but i will hopefully run for a long time, whereas i wouldn't have wanted to run the petrol much over 120k miles

IamNotAllowedToUseMyName

The risk of the DPF is mainly about engine design and driving style.

It seems anecdotally that some diesels (Corsa for example) are more prone to DPF problems than others. My theory is that some engines are inherently dirtier than others so the filter has to work harder, and also smaller diesels tend to be worked harder and therefore also produce more soot.

In terms of driving style, watch an old diesel car and notice when they produce obvious soot. A new diesel will be similar, hopefully producing less soot, but heavy acceleration and over-revving will clog up the engine.

So diesels are popular to drive because of the torquey sensation of their acceleration. 9000 isn't a no go for diesel but doesn't really make sense in terms of overall economy even though you should use less fuel. Whether you hit technical problems in part depends on where you live, how you drive and whether you have a nice efficient, modern diesel that is cleaner than those of a few years ago.

Trebor16

Have you looked at the prices the equivalent petrol models are going for in comparison with the diesels you are considering?