Hi all.
As someone who knows almost nothing about the technical nature of engines, could someone humour me with an idiots proof explanation to this:
Assuming all factors are the same (eg, drag co-efficients, weight, driving style etc), will a diesel engine car always be more economical than a petrol driven one? The reason I ask is that I've noticed that there is a VX Vextra 3.0 diesel available and am intrigued if that would be more economical than say the bog standard 1.8 version? Of course, I would just never entertain buying a 3.0l petrol car on the grounds of silly fuel economy, but wondered if being diesel made this a more sensible prospect?
Cheers.
TT
--
Top Turkey - the fastest hands in Brum
|
Depends on the characteristics of every car I guess.
Bear in mind that the 3.0 diesel engine itself will be considerably heavier than the 1.8 petrol and thus will probably require beefed up components - suspension, battery etc - which adds to the weight.
Obviously diesel is inherently more economical than petrol, but perhaps not as much as some contend; about 20% more for comparative cars in everyday driving.
Given the 1.8 Vectra is more than capable of transporting a salesman, complete with mobile phone, at highly illegal speeds in their natural habitat of the outside lane of the motorway, it is difficult to see a case for the diesel version; unless they want to tow a trailer displaying their goods.
|
|
Assuming all factors are the same (eg, drag co-efficients, weight, driving style etc), will a diesel engine car always be more economical than a petrol driven one? The reason I ask is that I've noticed that there is a VX Vextra 3.0 diesel available and am intrigued if that would be more economical than say the bog standard 1.8 version? Of course, I would just never entertain buying a 3.0l petrol car on the grounds of silly fuel economy, but wondered if being diesel made this a more sensible prospect?
As a general rule of thumb, petrol cars are 20-25% efficient whilst diesels are 40-45% (up to 50% for some very large diesels)efficient for their given CC's.
I would imagine that even the 3 litre diesel engine would give similar mpg to the 1.8 petrol unit, ie bad for a diesel but very good for a 3 litre petrol, one thing is for sure, the 3 litre diesel would perform fantastically compared to the 1.8 petrol !
|
If we bought fuel by mass and not Volume diesel would lose all its advantages on economy.
|
If we bought fuel by mass and not Volume diesel would lose all its advantages on economy.
>>
True, so lets hope they dont think of this one !
|
The current Vectra 1.8 petrol (122PS 126mph 0-60 10.5) gives 38.7 mpg combined. The 3.0 diesel (184PS 140mph 0-60 8.6) gives 40.9.
You can't compare purchase price directly as the 1.8 is available in every trim except Elite while the 3.0CDTi is only available in Elite trim.
A 1.8 Design is listed at £17395 while a 3.0CDTi Elite is £24945, a difference of £7550 but £2700 of that is the difference between Design and Elite - so the 3.0CDTi is £4850 more expensive!
|
A great deal depends on how you use it. A diesel engine is usually larger and so takes longer to warm up. If you're using the car for short journeys the petrol will take less time to warm up and so will operate to it's maximum efficiency much quicker than a 3.0 Diesel.
On long motorway journeys big engines are good news. They don't rev as highly and in the nice warm state are pretty efficient. A good example is the 6 litre Monaro. It'll do a crushing 8ish to the gallon over a couple of miles. On the motorway, expect a life affirming 25mpg.
|
Diesels don't need fuel enriching in cold weather, therefore they're more efficient from start-up, hot or cold.
Glow plugs assist very cold starting but most modern diesels don't need glow plugs until below 0c.
|
|
|
The problem is the massive torque at low revs in a 3.0 diesel could put such a grin on your face that you use the loud pedal a lot more, and forget all about fuel economy! I saw a post somewhere by someone saying his colleague only gets 25mpg from a BMW 535d.
Even when driving fast though, you should still get respectable economy compared with a petrol car being similarly driven.
A better comparison performance-wise would be with the SRi 2.0 turbo petrol (good Saab engine) with a lot less torque but similar power to the 3.0 diesel. But if you do less than 20k miles per year, the difference in fuel cost could be insignificant anyway.
|
> SRi 2.0 turbo petrol (good Saab engine)
The 2.0 turbo petrol used in Vauxhalls SRi is an Opel/Vauxhall engine not a Saab unit, although Saabs also use it.
It's a development of the C20LET engine used in Cavalier, Astra and Vectra.
|
|
|
|
|
<< will a diesel engine car always be more economicalthan a petrol driven one?
Don't forget that the price and cost of servicing may well be more expensive. I think a lot of people ignore these two factors. You may have to do a fairly high mileage in a diesel just to break even with a petrol. (Also don't forget the rapid deterioration of your Guccis caused by paddling in the inevitable pool of diesel at the pumps!)
--
L\'escargot.
|
Also the heavier engine/gearbox weight of a diesel cause greater wear & tear on suspension & brakes. I did a spreadsheet last year when I looked at getting rid of the alfa and even with my high mileage the difference in fuel costs was only £ 1,200-£1,800 or so which was small in relation to other costs, such as depreciatio & higher maintenance.
|
'(Also don't forget the rapid deterioration of your Guccis caused by paddling in the inevitable pool of diesel at the pumps!)'
In 99.9% of fuel stations I use all grades are available at every pump, so I'm standing in diesel whatever I am filling with!
The days of one solitary diesel pump located at the back of the station are thankfully long gone!
|
|
|
The average motorist in this country could never get his money back between the cost of a diesel and petrol.In Germany where there is a difference in the price of Diesel to petrol of 20cents you need to do over 25k a year in a Audi a4 to break even.The road tax is far higher on diesels which is a disadvantage though.Increases in road tax have just about killed the secondhand 4x4 diesel market it cost as much to tax as the car is worth.
|
Plus the bottom of the 2nd hand diesel market is about to fall out in a big way, when all these supercomplex commonrail engines start to fail and be imposible to fix economically...I foresee the ´96-97 Xantia TD estate appreciating in value over the next 5 years!!! You heard it here first.
|
Funnily enough good Zantia diesel estates fetch good money especially with high trim levels.A super car.
|
|
|
"Don't forget that the price and cost of servicing may well be more expensive"
please explain - why? Also see other thread on comparitive cost of diesel/petrol servicing
www.honestjohn.co.uk/forum/post/index.htm?f=2&t=38...5
--
Phil
|
I'm hanging on to my Pug 205 diesel.
|
|
|
|