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# 2 Questions about fuel and fuel economy maths genius or car experts required

2 things that I can't decide on myself first now with diesel nearly everywhere at least 12p a litre more than petrol and saying (please correct if wrong) diesels do about 48 miles to the gallon petrol 32 is there any saving by buying a diesel car.

2nd i was in drive through Kentucy today and guy in front stopped and started his car everytime we moved being a sunday this was about 10 times i can only guess for fuel economy reasons was he wasting his time or would starting the car this many times in approx 5 mins see any fuel saving undone by wear on starter and the fuel required to
start the car each time

Thanks Guys and Gals

not sure about the first bit but ive been told its less economical to keep starting the engine before you add in the wear and tear!

If petrol is £1.10/l (£4.99/gal) and diesel is £1.22 (£5.54/gal). Then the petrol car at 32 mpg it costs £0.156/mile, where as the diesel car costs £0.115/mile, so it is cheaper with the diesel.

Not sure where you got your mpg figures from but if diesel is 50% more efficient and 10% more expensive, as your figures suggest, it is clearly more economical. Reality depends on much more - the amount you drive, the type of driving (city/long distance), how much they cost to service, what size/power car you want etc etc. Even then I doubt many diesels are even close to 50% more efficient compared to modern, fuel-efficient petrol engines..

I am having the same dilemma and as a Mathematics teacher thought I would work it out for an average car, so here goes...

Over 3 years and based on a Ford Focus 1.6 petrol zetec 3 door and a Ford Focus diesel zetec 3 door, assuming annual mileage of 12000 miles and using fuel consumption figures provided by Ford and depreciation figures provided by WhatCar magazine;

Initial Cost Depreciation Road Tax Fuel* Total

Petrol £15245 62% - £9451.90 3 x 145 = £435 £4087.62 £13974.52

Diesel £16745 63% - £10549.35 3 x £35 = £105 £3029.04 £13683.39

*Uses todays prices at my local supermarket - 108.9 petrol and 119.9 diesel.

Of course, these figures rely on getting the cars at MRRP and of course that almost never happens, but it strikes me that, based on this estimation, unless the diesel is within £1500 (ish) of the price (and remember that petrols are often discounted more than diesels), it is probably better to get the petrol. But...each to their own...

Interestingly, WhatCar magazine say that the petrol is almost £700 less to run over 3 years and 36000 miles but they include insurance and servicing in their calculations...hope this helps!!!

sorry...my attempts at a table were not so successful!!! Also, these days there are engines, as mentionned above, that have better economy as a petrol but diesel technology moves forward just as quickly. ECO models from all the major manufacturers are diesel based and have fuel economy as a clear advantage.

NB I am a petrol driver - I can't stand diesels personally!!!

but diesels dont depreciate as fast and if your working over the entire life of the car, a diesel most of the time will go round the clock twice where a petrol usually doesnt!!

Diesels didn't depreciate as fast but now there are many more people asking similar questions to these - the price differential between petrol and diesel is now at the point where there is a realistic choice between buying petrol and diesel as the above figures show. I do acknowledge that there seems to be better longevity with diesels but this isn't always true either. Seems to me it is about taste these days. If the difference between diesel and petrol increases further, buy petrol!!!!

Beninlincs;2767248
Diesels didn't depreciate as fast but now there are many more people asking similar questions to these - the price differential between petrol and diesel is now at the point where there is a realistic choice between buying petrol and diesel as the above figures show. I do acknowledge that there seems to be better longevity with diesels but this isn't always true either. Seems to me it is about taste these days. If the difference between diesel and petrol increases further, buy petrol!!!!

no no no shhhhhhhhhhhhhh lol

maybe i could persuade the oh to trade it for something a lil more sporty on your workings:thumbsup:

it also depends on how you drive your car also, if you are mainly driving in the city then there isnt much difference in fuel econemy, but the difference comes when you travel at higher speeds i.e. motorways. So if you drive in the city i would say petrol, but for long distances i would say diesel.

one thing to remember in the calculations is , diesel cars are more expensive than their petrol equivalents (how ever you spell it )

I still don't understand how suddenly diesel has become more expensive than petrol, did forget to send me the memo? It's still cheaper than petrol abroad, so what going on (apart from usual fat cats getting obese-er)

Banned

Was it not from further increased "green" taxes on diesel?

guv;2768277

Was it not from further increased "green" taxes on diesel?

No, fuel tax per litre of road diesel and petrol is the same at 50.35 p.

It is due to supply and demand in the UK and the massive shift towards diesel usage.

Banned

Ah, ok. So its basically greed!

guv;2768322

Ah, ok. So its basically greed!

Not really, limited refining and import capacity for diesel compared to petrol.