diesel really much cheaper than petrol?

toasterman

Hi everyone,

I've always thought that if you wanted a car that was cheap on fuel, you buy a diesel - but now I'm not so sure.

I've done some calculations using the quoted MPG from the Parker's guide Dec07, and assuming petrol is 1.02 a litre, and diesel is 1.07 a litre, and there are 4.5 litres to the gallon. I know these are all estimates, and I know petrol and diesel can be got cheaper, but this seems to be about average (modal) for my area at the moment.


From my calculations, doing 15000 miles, it would cost on fuel:

£1,062 in a 1.4l diesel Toyota Aygo
£1,121 in a 1.0l petrol Toyota Aygo
Now I know it's cheaper, but only by £59 over the course of 15000 miles.


Some more...15000 miles...
£1,111 in a 1.5l diesel Renault Clio
£1,464 in a 1.1 petrol Renault Clio
Again cheaper, but only by £353 over the course of 15000 miles, and thats one of the biggest differences on mpg between petrol and diesel. 47mpg for petrol and 65mpg for diesel.
The diesel model is also 2 insurance groups higher AND a few hundred pound more expensive to buy.


In bigger cars, there's almost no different at all...15000 miles
£1,639 in a Toyota Corolla 1.4l petrol
£1,537 in a Toyota Corolla 2.0l diesel.

£102 saving over the course of what? A year for the accepted "average" driver of average mileage?
Again the diesel is 2 insurance groups higher and more expensive to buy as well.



I always thought diesels were a lot cheaper to run, but I guess I'm wrong - unless I'm missing something here?

I know diesel was once cheaper than petrol...that clearly makes a difference.
My old Rover 214 is too old to be in Parker's, but the 1995 model (one year younger than mine) apparently does almost the same mpg as the Corolla above. My current 15000 miles costs me £1,738 and it was £500 to buy the car.
I guess the only way I could save money on my fuel is to get a smaller car.

pennypuppy

Well thought out. You are right too, the only way to go is smaller cars...it's inevtiable. I drive a scenic and love it but the fuel efficiency in town is not great. Mind you I detest those big monster jeep things which swagger about and take over the road. Some of the fiats have good fuel consumption but my biggest concern is the crash tests and what the safety ratings are.

I live in Derry Northern Ireland, its only a couple of miles from the republic. Everyone here fills up their cars over the border...much cheaper.

ManAtHome

I think diesel was around 75% of the petrol price around 10 years ago. Dunno whether it was changes was to company car tax (sure they made diesels more attractive) that changed the supply/demand curve or whether the "curve change" made increased taxation of diesel more attractive.

toasterman

I use my car for work is the thing.
While my employer doesn't really have any right to tell me what car I should be driving, my job would be harder with a 3-door smaller car as I do need to get things in and out a lot.
I also frequently need to deliver things, so the Aygo used in my example is a poor choice of car - I'd have it stacked to the roof the whole time.
My current car isn't what I'd call huge, and i think any smaller and there would be an issue of legroom as me and my friends are all around 6ft.
I dare say I'd manage with a smaller car, but I like to make life easier for myself.

The corolla would be more of a sensible choice, but I do find it interesting that in a lot of cases, because of current fuel prices, the difference is very minimal between petrol/diesel. I spoke to a friend who has recently relocated to Germany, and fuel seems about as pricey there as it is here, although diesel and petrol are priced the other way around - with diesel being the cheaper.

It was more of an exercise really - as one garage recently told me my gearbox is on the way out, and another told me it was "very noisy in first, second, and fifth gear". Plus as its a petrol Rover 214 (not the bubble shape) with a k-series engine, and 80k on the clock, I'm expecting head gasket failure any minute now. Thought I'd start looking/saving now while it's still going. I'm determined to buy my next car without resorting to overdraft or credit/loans/finance agreements.

Conor_3

Basically, a diesel car gets 40% more miles per gallon than the same sized engine petrol car. For example, I get 37MPG from my 2L Capri and my last 2L Petrol Mondeo but my new 2L diesel Mondeo never returns under 52MPG.

Diesels are cheaper but only if you buy them second hand as the increased price over a petrol counters any savings on fuel for about 3 years.

The_Biff

Two points here:
1) Diesel cars may cost more but they are worth more when sold on.
2) "Which?" car supplement notes that a lot of claimed (by manufacturers) mpg figures are wrong. The actual mpg figures are always stated by Which?magazine.

highguyuk

Well the which magazine would say that ... :P

toasterman

The_Biff wrote: »

Two points here:
1) Diesel cars may cost more but they are worth more when sold on.
2) "Which?" car supplement notes that a lot of claimed (by manufacturers) mpg figures are wrong. The actual mpg figures are always stated by Which?magazine.

I assumed all mpg figures were wrong, as they were all done in lab conditions, rather than real world conditions. On that basis, I assumed they'd all be wrong by a roughly similar amount. What else can you go on really - because unless it's the same person driving every car at Which, that won't be a reliable test either.

toasterman

Conor wrote: »

Basically, a diesel car gets 40% more miles per gallon than the same sized engine petrol car. For example, I get 37MPG from my 2L Capri and my last 2L Petrol Mondeo but my new 2L diesel Mondeo never returns under 52MPG.

Diesels are cheaper but only if you buy them second hand as the increased price over a petrol counters any savings on fuel for about 3 years.

According to Parkers, a current 2l petrol Mondeo does 33mpg, while a 2l diesel can get as high as 48mpg.
However - a 2l petrol Mondeo and a 2l diesel Mondeo don't have the same power, surely?

I mean you get 1.0l petrol Corsas, but you don't get 1.0l diesel Corsas.

According to Parkers, using a Mondeo as an example, the 1.8l petrol Mondeo has 123bhp, 35mpg, top speed of 125mph.
The slowest 2.0l diesel Mondeo has 113bhp, 45mpg, top speed of 121mph.

So really for a fair comparison, should I be comparing a diesel with a smaller petrol engine? Or does the petrol engine have to be ranted to compare?

Woby_Tide

we switched from petrol to diesel a few months back(1.6 to 1.6), based on the offical figures I was meant to save about £200 per year in fuel costs which covered the 'diesel premium' of the new car in about 5 years. After 5 months I think we've 'saved' about £40 on average per month, this month however is looking to be about £90 because of the way our refuelling cycle has landed. I reckon by year end we'll have saved about £5-600 against our petrol costs(all things being equal with the actual rise in fuels) so way above expectations, and over the 5 years we estimate dthat gives us an extra couple of grand. The petrol MPG was way off on old car, teh diesel MPG is off by a bit but not as much is the main difference

Conor_3

toasterman wrote: »

According to Parkers, a current 2l petrol Mondeo does 33mpg, while a 2l diesel can get as high as 48mpg.
However - a 2l petrol Mondeo and a 2l diesel Mondeo don't have the same power, surely?

According to Parkers, using a Mondeo as an example, the 1.8l petrol Mondeo has 123bhp, 35mpg, top speed of 125mph.
The slowest 2.0l diesel Mondeo has 113bhp, 45mpg, top speed of 121mph.

So really for a fair comparison, should I be comparing a diesel with a smaller petrol engine? Or does the petrol engine have to be ranted to compare?

OK...
Firstly, I'm good at economical driving - one of my employers put me through a course. It's worth doing as not only do you increase economy but reduce journey times as well.

As for the Mondeo, the 2L diesel is I drive is actually about as fast as the petrol. The car I'm referring to in this case is a Mondeo 2L 130TDCi. It has 130BHP but more importantly over 250 ft/lb torque which is a hell of a lot more than the petrol. I can show you the trip computer at any time you wish and it won't be showing less than 52MPG and I don't exactly crawl about.