Cost running petrol v diesel - MB
This may have been covered before but has anyone worked out the costs of running two similar cars - one with a petrol engine and another on diesel.
I am interested in two scenarios - buying new and at, say, three years old.

What sort of milage do you have to do each year to make the diesel viable?

You will pay more for a diesel - particularly at three years old - but it will depreciate less from new.
Servicing is supposed to be more expensive on diesel - is that really true. Are there other factors to consider?

I am not interested in better driving styles - just the the cold hard economics of it.

It seems to me that if you are buying new then diesel makes sense - buying used at 3 years petrol wins out - what do you all think?
MB
Cost running petrol v diesel - mlj
Cards on the table to start with; I am pro diesel from an economic and driving point of view.

However, I now drive a petrol. Why? The economic argument.
To get high mpg you probably need to go VAG TDI or PSA HDI. It depends then on which petrol car you are going to compare it to. Find out exactly what mpg you are likely to get in your own circumstances.
Then you can compare through annual mileage and current fuel costs.
Servicing; difficult to generalise but I will anyway. Routine diesel servicing is perhaps marginally more expensive. £20-30 a time in my experience. At once a year inervals that does not constitute a decisive difference. Diesel engines have greater longevity and less to go wrong. This is a contentious and personal view, based on 20 years experience of both over many cars.
I bought my petrol engined car £3000 cheaper than the diesel equivalent. I now drive 8K per annum compared to 20Kpa. The mpg differential on my make/model is 10mpg. It would take a very long time to recoup the extra £3K.

However, if the mpg differential is 25, and it can be, and you drive 15Kper annum plus the initial price difference can be quickly justified.
My advice is to ignore the servicing cost issue, it is marginal.
Final fact; I traded my Golf TDI in for a new Leon TDi 2 years ago. It was 7 years old, FSH, reasonable condition, white, and had 120K under its' belt. It was underwritten at £3K and I got £3250.
I wouldn't have got anywhere near that for a Golf 1.6, say.
Cost running petrol v diesel - 8 ball
It seems to me that if there is no difference in the price of a diesel -v- its petrol equivalent it would be better to go for diesel every time. And if performance is about the same (0-60 & top end) plus more torque from a diesel, it would seem strange to buy a petrol car that was over 10 mpg worse than its diesel equivalent. Or am I wrong?

8 ball
Cost running petrol v diesel - Cardew
MB,
I would agree with the conclusion in your last paragraph, although the 2 factors missing in your scenario are what category of car are you considering - VW Polo or S Class Merc - and how long do you intend to keep the car.

My brother runs a taxi business and the high annual mileage of his cabs make diesel the natural choice of most drivers.

He reckons that for a Mondeo size car, the diesel car will have an advantage of about 10-12mpg over a petrol version when driven in a similar manner.

So for a 10K a year motorist the fuel savings are in the region of £250pa. I guess the difference in other running costs is small.

In my opinion the economic advantages of a diesel are marginal when set against overall running costs.

C
Cost running petrol v diesel - MB
Yes I should have said that I'm thinking about Mondeo-sized family cars. Given the comments above it looks as though you've got to be doing around 16k a year to make the diesel a worthwhile purchase.
I am also right in saying that 3-5 year old, high milage diesels can develop expensive problems - more so than their petrol equivilents.

Lots of people on this site with older diesels seem to report big bills at this age - the sort of bills that would wipe out their fuel savings for the previous two years.
MB
Cost running petrol v diesel - Phoenicks
I would say the £250 p/a cost saving isnt a lot really in the scheme of things. To put up with the diesel clatter, the billowing smoke and the horrible diesel on hands issue when filling up, the costs have to be a lot more beneficial. Also they may pull harder in gear, but they are a bit empty in driver satisfaction to pull to 4500 max with little power thereafter.

The only diesel i would consider is the bmw 330d or 320d having experienced them they are excellent and not too grumbly.

I think the main benefit of a diesel isnt the cost but the fact you only have to fill up every 2 weeks rather than every week!
Cost running petrol v diesel - DavidHM
I like driving diesels - as long as they have enough power.

New, I would say most times, go for the diesel, because of the lower depreciation and better economy, especially given that drivers of newer cars tend to drive them more, having more money to do so - but even at 12k pa, if you keep the car for a relatively short time (<4 years), you'll probably get all the initial premium back.

Used, I think it would probably take about 20k pa to justify the cost saving, although I am not sure that it's fair to say that diesels cost more in repairs as these engines tend to be less stressed over bigger mileages, although if you're unlucky I suppose things can cost way more.
Cost running petrol v diesel - Altea Ego
Here is a comparison, taken from a fleet operators database.

Car is Laguna Dynamique, operating cycle is three years. Figures include depreciation, maint, fuel, - but no insurance, in Pence Per Mile

1.8 Petrol, 10k miles year=40.86ppm, 15k miles year=35.13ppm, 20k miles year=30.04ppm
1.9 Diesel 10k miles year=39.88ppm, 15k miles year=33.37ppm, 20k miles year=27.26ppm

So For diesel you save

@10k miles year £98 pounds a year
@15k miles year £264 pounds a year
@20k miles year £556 pounds a year.

This calculation is ONLY accurate on a new car, purchased and sold after three years.


Cost running petrol v diesel - RichardW
There was just such an article in Diesel Car (I think) a while back - based on an A4. I can't remember the exact figures, but ISTR the diesel was about 20%. Still, they were talking of the order of 50p/mile PLUS insurance - which compares very badly indeed to the 17p/mile all in my Xantia costs. I might see if I can find it later on.


RichardW

Is it illogical? It must be Citroen....
Cost running petrol v diesel - Cardew
RF
"Car is Laguna Dynamique, operating cycle is three years. Figures include depreciation, maint, fuel, - but no insurance, in Pence Per Mile"

Those figures surely must include other cost factors such as RFL and the cost of borrowing the capital to buy the car.

It would be interesting to see a breakdown of the figures and particularly the depreciation figure.

Taking the 20k pa petrol car you give as an example. The total costs for 3 years would be 60,000 x 30.04 = £18,024.

Now assuming consumption at 35mpg, the cost of fuel would be approx £5,850 over 3 years, and even adding a high figure of say £1,000 for maint. That comes to £6,850. So there are other costs of over £11,000 to be accounted for.

The Laguna depreciates heavily but also fleet buyers get them at rock bottom prices. What would be a reasonable depreciation figure for a 3 year old 60k car?

C


Cost running petrol v diesel - RichardW
"I am also right in saying that 3-5 year old, high milage diesels can develop expensive problems - more so than their petrol equivilents.

Lots of people on this site with older diesels seem to report big bills at this age - the sort of bills that would wipe out their fuel savings for the previous two years."

Erm, where's that then...? Apart from the spate of con-rod failures on XUD engines which affected maybe a couple of hundred of the 8 or 9 million units built, and the problems with the Ford TDCi injection pump there are no common themes I can think of. Granted most OLDER diesels will need a new set of glowplugs at around 8 years old, but this is cheap (DI engines hardly need plugs these days).


RichardW

Is it illogical? It must be Citroen....
Cost running petrol v diesel - daveyjp
The full life costs are interesting, but who considers these when buying? I bought a diesel so I could get 200+ miles from 20 litres rather than 130-150 miles I was getting. The main cost associated with running a car is fuel as this is the most frequent item of expenditure. Spending so much less on fuel is what I notice, not the fact that it may be costing me £20 a month extra to actually buy the car.
Cost running petrol v diesel - OldPeculiar
One (relatively minor) cost niggle I with with Diesels is car tax. My 1.5 diesel is taxed at the same rate as a 1.5 petrol despite the fact that it uses less fuel (and produces less pollution) than the 1.1 litre petrol!

Since on many models you need to buy a larger diesel engine to get the same performance as petrol this does add to the comparative cost.
Cost running petrol v diesel - daveyjp
The whole car tax system is a complete mess since it was changed from a flat rate to first a variable rate based on engine size and then to variable rates based on emissions. (Try taxing a smart car!)

On the lower rates there is a £10 premium for diesel engines (the tax on my diesel is £80 as opposed to £70 on our petrol car with similar emissions).
Cost running petrol v diesel - Leanne
I compared a Fiesta Zetec 1.4 petrol to a 1.4 Zetec TDCI. Only optional extra was metallic paint.

I assumed a residual value of 40% afer 4 years (based on parkers figures for a Focus - crude I know.)

I used the combined mpg figures produced by the manufacturer.

THe TDCi cost £1000 more initially, but worked out £1000 less over 4 years, based on 12k miles per year.

I allowed for jam-jars prices in the calculations, not list prices. I also got free insurance and road fund licence for the first year.

Over 3 years the total costs were quite similar.

I suppose the risk is if I get a big bill after the 3 year warranty runs out.

I have calculated that the TDCi will cost £200 per month including depreciation, fuel, servicing, insurance and road fund licence. No credit charges as I saved up for ages for the car.

I am now saving the equivalent of the depreciation so I can get a new one in 4 years. Saves a fortune on interest!

 

Value my car