Comparing Petrol to a Diesel (doing tha maths!)

Found 8th Aug 2008
I hope someone here can help me.

I am stuck between getting a petrol or diesel vehicle for travelling to work each day in the near future.

Diesels generally cost more to buy, and the Diesel fuel is also more costly so I am finding out by doing some maths if a diesel really is worth getting.

The two vehicles I am comparing are the BMW 320i Auto and BMW 320d Auto

#### BMW 320i auto

fuel cost : 114.9 / litre
1 Gallon costs £5.22
vehicle mpg : 25.7
Full tank does 356.15 miles
Full tank costs £ 72.34

#### BMW 320d Auto

fuel cost : 127.9 / litre
1 Gallon costs £5.81
vehicle mpg : 31
Full tank does 429 miles
Full tank costs £ 80.52

Now, in terms of consumption, you get 20.5% more out of a diesel BUT the fuel cost is 11.3% more.

So, my conclusion is that its not REALLY a massive amount better to get a diesel as the car itself costs more as well. Keeping it on average of two years, doing approximately 15k a year is not a massive saving. So I should just go for the petrol ...?

Your views are very much appreciated !!

Thanks

35 Comments

BMW are always better in diesels!!!

whats the difference between the price of the cars?

Diesels do cost more but their resale values also tend to be a bit higher (as diesel engines last longer).

Banned

I think for BMW you should stick to petrol,I am getting a new peugeot 308 on the 1st september but will be getting a diesel this time as I will nearly double the miles for nearly the same cost so this would be best for me.

A number of points...

You have not factored in differences in servicing costs, tax costs nor resale premium of the diesel.

You have, also, selected about the most uneconomical diesel I have seen for a long time. Have you checked that figure?

Finally, you have given a very specific example with poor-ish savings, there are many huge savings out there.

As I thought, even the "old" (98-05) 3-series 320d auto appears to do 40 MPG. The newer one appears to be 42.

Banned

Please remember diesels on average require servicing every 8-10,000 miles whereas petrol can go 12-14,000 miles.

Diesel cars make more noise

Banned

Scream;2702615

Diesel cars make more noise



not much more these days;-)

Original Poster

Naeem786;2702530

BMW are always better in diesels!!!



... but why ??

guerilla;2702541

whats the difference between the price of the cars?



around £2000 at the ones I am looking at. Petrol costs 10.5 k , diesel costs 12.5 k ... and the diesel has done a lot more miles!

pghstochaj;2702567

A number of points...You have not factored in differences in servicing … A number of points...You have not factored in differences in servicing costs, tax costs nor resale premium of the diesel.You have, also, selected about the most uneconomical diesel I have seen for a long time. Have you checked that figure?Finally, you have given a very specific example with poor-ish savings, there are many huge savings out there.



Servicing is different for each car, apprantly it depends on how they are driven too.

that figure is taken from autotrader ... the URBAN miles (not combined, which I think yo uare looking at). It does not matter what you compare by the looks of things, the differences are all proportional.

what other savings are there ??

pghstochaj;2702576

As I thought, even the "old" (98-05) 3-series 320d auto appears to do 40 … As I thought, even the "old" (98-05) 3-series 320d auto appears to do 40 MPG. The newer one appears to be 42.



I think you are looking at the combined mileage, I was looking at the urban. Either way, like for like, the calculations bring out the same results.

Original Poster

podd2000;2702642

not much more these days;-)



I was actually quite surprised how noisy the 320d was ... was not quiet at all.

interestingly BMW came in last place in the industry reliability tests last year (european manufacturers)

if you are buying an older car - do remember that if you do have a problem with a diesel engine it is usually more costly and difficult to put right than a petrol engine (especially in relation to the fuel pump - £1500)
Shouldn't be a problem if you are getting a car that isn't too old.

if you can get a petrol that is 1-2k cheaper I would take it - unless you are planning to do long journeys

also unless you are dead set on a BM, i would recommend considering other cars because they arent great on fuel consumption anyway,

I personally wouldnt consider any car that doesnt do more than 40mpg - was talking to my uncle yesterday who's a car dealer and he says he is finding it much more difficult to sell cars like BM's and mercs that only do around 30mpg.

As diesel cars last longer and the re-sale value is always greater if it was a petrol engine! I am going to buy a diesel in the next 1-2 months as my petrol car is a killer to run!!

cyrus - your def doing the right thing working it all out and figuring what it will all cost.
So many people dont and only figure out later that it costs a fortune to run
the parkers website is good for comparing cars / consumption / tax / running costs etc

[url]www.parkers.co.uk[/url]

Cyrus;2702646

Servicing is different for each car, apprantly it depends on how they are … Servicing is different for each car, apprantly it depends on how they are driven too. that figure is taken from autotrader ... the URBAN miles (not combined, which I think yo uare looking at). It does not matter what you compare by the looks of things, the differences are all proportional.what other savings are there ??I think you are looking at the combined mileage, I was looking at the urban. Either way, like for like, the calculations bring out the same results.



Not really, generally, diesels do much better MPG at speed than around town, with respect to petrols. I think you will find that on the petrol you will get 25-35 MPG and the diesel 35-55. Hence where book figures become less useful.

The savings of a diesel are on tax, resale value and additional MPG. For the petrol, you may save on servicing and original purchase price. If you want an accurate review, it is a lot more complex than comparing one book MPG figure with another.

What will your commute look like?

Original Poster

thanks all so far ..

I will be doing around 15k a year for which I will pay for and anything extra will be paid by the company.

I want to get a car that is around 4 years old ... I find the prices depreciate best then so I will be able to hold onto something while keeping it for 2-3 years.

I'd choose a more economical BMW. My mate's 2 litre BMW diesel is an 03 reg and does 80mpg+ on the motorway (I have a photo somewhere on my phone showing the computer!)

Original Poster

Its a good point to make, that I will be doing mostly motorway miles.

Cyrus;2702937

Its a good point to make, that I will be doing mostly motorway miles.



Then why did you compare urban MPG?!:?

Original Poster

pghstochaj;2702989

Then why did you compare urban MPG?!:?



because I want to look at in worst case, as the manufacturer figures are not always something to trust. and also because the differences are the same doesnt matter if you compare urban, combined .... whatever really.

I've not had time to read through all the other posts in here but also bear in mind that services tend to cost more in diesels as do most parts if you need to get anything repaired.

On that mileage you probably won't see much of a difference between petrol and diesel in terms of TCO

I used to do about 30,000 miles a year and went from a Petrol VW to a Diesel, all the sums added up, and I probably saved about 25% a year on fuel costs, however the extra costs to buy, plus some hefty repair bills kinda wiped that all out.

The best savings I've found are to adjust your driving style, use cruise control etc. if you have it and accelerate more progressively, could usually stretch at least another 10mpg in the 2.0 tdi VW this way.

worto03;2703136

I've not had time to read through all the other posts in here but also … I've not had time to read through all the other posts in here but also bear in mind that services tend to cost more in diesels as do most parts if you need to get anything repaired.



In my experience repair bills tend to be more in diesel, new injectors, glow plugs etc ain't cheap and if the engine starts losing compression it's big money!

Cyrus;2703006

because I want to look at in worst case, as the manufacturer figures are … because I want to look at in worst case, as the manufacturer figures are not always something to trust. and also because the differences are the same doesnt matter if you compare urban, combined .... whatever really.



It's not the case though, especially not in reality. In practice, the diesel will get 50 on the motorway, the petrol 30-35.

Tillboy;2703158

In my experience repair bills tend to be more in diesel, new injectors, … In my experience repair bills tend to be more in diesel, new injectors, glow plugs etc ain't cheap and if the engine starts losing compression it's big money!



Same with a petrol, though, of course. Hence why you select the correct car to not have such issues. New injectors (and fuel pumps, as suggested previously) are hardly things you have to consider under normal ownership, especially if the OP is only looking at running the car for 30-45k before selling.

pghstochaj;2703205

Same with a petrol, though, of course. Hence why you select the correct … Same with a petrol, though, of course. Hence why you select the correct car to not have such issues. New injectors (and fuel pumps, as suggested previously) are hardly things you have to consider under normal ownership, especially if the OP is only looking at running the car for 30-45k before selling.



yeah just generalising, which is difficult in this case as there's so may factors, i was quite unlucky with my last car as when the warranty expired I had some hefty repair bills, which if I'd chopped it in before 60,000 miles wouldn't have been a problem.

I do a lot less miles now so lease my cars so they're always in warranty so no issues...

Banned

Just a thought why a BMW ? why not a smaller car"less tax"

Original Poster

podd2000;2703254

Just a thought why a BMW ? why not a smaller car"less tax"



i like my cars and want something with a bit of punch ... and decent space (Golf being the smallest I would buy).

I just cant find any cars out there that are reliable, have good consumption and are fun to drive.

Watch out with DPFs you spend all your time driving carefully to keep fuel consumption down, then the blasted light comes on and you have to hammer it for a few miles to clear the filter

Best diesels are from the VAG group - 150/170 bhp as standard, but still return 50+ mpg

£125 road tax too

£400 remap would take the power to around 200bhp (330lb/ft torque)& 55mpg on a decent trip = VERY FUN

With your budget, I'd get an 06 MK1 Leon FR+ TDI (no DPF on the MK1 Leon either)

Original Poster

Thanks Chris but a) I need an AUTO transmission car and b) The leon is fugly man !

This link is a few months old but interesting reading none the less:
thisismoney.co.uk/con…d=5

Why do you need auto ? Lazy git lol

Cyrus;2706074

Thanks Chris but a) I need an AUTO transmission car and b) The leon is … Thanks Chris but a) I need an AUTO transmission car and b) The leon is fugly man !

Another reason to get a VAG... The DSG auto is fantastic

Original Poster

ChrisUK;2709110

Why do you need auto ? Lazy git lol



lol , my left ankle is damaged and i find it difficult to drive a manual (even though I prefer manual!)
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