crikey, what car does that??

Simple physics will tell you that it makes no difference

Simple physics yes, not the complicated real world physics of engines 🙂 When you drive a car harder that may mean lower gear and/or more throttle. So that means more losses, more heat loss, more unburned fuel exiting the exhaust, not to mention the effects of variable valve timing and about a million other things.

As for diesel/petrol in terms of performance and economy, check out the Audi TT diesel and petrol versions. Same car, very similar performance, very different mpg.

And whoever quotes 30mpg as an example of good fuel economy is living in the 60s aren't they? 🙂

i used to often get 55+mpg average on one tank in my old ('98) Seat Ibiza 1.9d. used to check what went in at the pump against how many miles i'd driven.

that included relatively short trips and use for work (i.e. rush hour).

As for diesel/petrol in terms of performance and economy, check out the Audi TT diesel and petrol versions. Same car, very similar performance, very different mpg.

40mpg vs 50mpg

People seem to overstate the difference between diesel and petrol.

30mpg used to be what you'd expect from a 1.6 Ford Escort, not a car with 340bhp that does 178 mph. Point being, petrol engines have improved too.

im pretty sure you already new the answer to the original post when you started the topic…you just wanted to brag about your diesel which every1 already has…

On average i get the same as the op from the same motor. You can thrash it and get about that or you can be very frugal and get 58mpg but it is only recommneded if you have the time and patience.

Been clocking fuel consumption on my latest for the last 5yrs and turned in repeatable results over this time, and for the last year i've taken to switching the engine off when waiting in traffic and at lights. Since doing this i've got an extra 2-4mpg every tank.Apparently it's something the Germans do as a matter of course, and car manufacturers are now automating.

I find those gages to be miles out showing 200mpg

They work both ways, as I've proved with my Passat. 1st time it said summing like 49.7 when in reality it was 47.9 then on a trip to Ft Billy last year it said 52.2 but on filling up at Morrisons in Ft Willy it was actually 53.7.

The torque on my Toyota Verso doesnt really climb until around 2000rpm, I was under the impression I would be better keeping the engine above this rpm as the engine is producing more torque for a given amount of pedal movement, than keeping it below where I need to press the pedal more as it is underpowered. But some of the posts above about staying under 2000rpm make me question whether Im right.

Though it is very dull to always change gear before the turbo spins up. I usually keep the revs between around 1500-3000rpm.

The torque on my Toyota Verso doesnt really climb until around 2000rpm, I was under the impression I would be better keeping the engine above this rpm as the engine is producing more torque for a given amount of pedal movement, than keeping it below where I need to press the pedal more as it is underpowered. But some of the posts above about staying under 2000rpm make me question whether Im right.

Though it is very dull to always change gear before the turbo spins up. I usually keep the revs between around 1500-3000rpm.

Is it petrol or diesel?

And if it's a diesel, are you sure it's the torque or the power you're noticing? Power of course being a multiple of torque and engine speed.

Most diesel engines produce their peak torque at below 2000rpm these days, but it should also be noted that the peak torque is the point in the rpm range where you are getting the most complete burn of the fuel in the cylinder per revolution. Not necessarily the point where it's using the least fuel… OK, sorry, perhaps not the best explanation, but whilst using a diesel's strong torque to accelerate it quite quickly but without revving to high (where the engine becomes inefficient) is more efficient than in a petrol, but may also not be quite as fuel efficient still as trickling it very slowly along, changing gear before the turbo spools up even.

Unlike in a petrol engine, the amount of diesel squirted into the engine by your injectors is directly proportional to how hard you press the accelerator. So tickling it gently of course will yield the best results. Accelerating hard before the turbo spools up will of course be very poor for your fuel consumption, as you won't be accelerating very much (because of lack of turbo pressure) but you're still using lots of fuel.

Driving a diesel for optimum economy is a trial, as it requires some quite different approaches depending on your speed, engine speed, incline and all sorts of other variables. Driving a petrol for maximum economy is much easier, as you just need to lay off the loud pedal as much as poss… That said though, of course a diesel will give you much better economy anyway!

Fifth Gear tested the recent Porsche 911 and got 30 mpg out of it, and i think it had well over 300bhp.

I remember Gordon Murray saying about his own McLaren F1 (he designed it by the way for those that don't know) that he used to get 26mpg whilst cruising down the motorways at "normal" traffic speeds (ie. 75-80mph). That's with a 6.1 litre V12 that produced 627bhp! Might've had a fair bit to do with the F1's low weight of just over 1100kg though in fairness…

Have had 32mpg out of a 1995 4 litre V8 Beemer 5 series myself on a 70 mile run before… That said I'm sure it was much easier to achieve 30mpg out of a new Porsche though, seeing as they have direct injection and are pretty efficient for a modern large capacity petrol engine.

They work both ways, as I've proved with my Passat. 1st time it said summing like 49.7 when in reality it was 47.9 then on a trip to Ft Billy last year it said 52.2 but on filling up at Morrisons in Ft Willy it was actually 53.7.

I'm not talking about the average ones, I was quoting a reference to the constant ones.

Rich – the slower the engine speed the more time the fuel has in the cylinder to combust properly. However getting the same power As for changing before the turbo spins up, that must be a bad idea. The car often overfuels in order to get the turbo spinning, so you might well be pouring in fuel without enough air which would be wasteful.

As for the Audi TT, as far as I can tell it's 37mpg for the petrol combined and 53 for the diesel. That's a fair difference in my book. It means, based on a 45 litre tank, another 160 free miles each time you fill up, or 45% extra. Not bad is it? And that's the cutting edge highly efficient TFSI petrol engine which is about as good as it gets for petrol.

As for your Passat gague showing 200mpg, that's your instantaneous mpg at that very instant ie when decelerating or going down a hill. If it says 200mpg for a whole trip then it's got something wrong with it 🙂

got a 55 plate Golf GT TDi and i can get 65+mpg on a slow motorway drive. Average about 56/7 though even with a heavyish right foot.

If i want to be frugal then it's AC off, and change gear just as you reach the top of the torque band when accelerating (about 2300RPM i think) There's little reason ever to take an engine with that much torque over 3000 RPM, also stay in a high gear when braking for as long as possible until you feel the engine management fighting back, try to go to neutral at the latest possible point. You get best result by driving smoothly, taking corners well without changing speed much and by thinking a good 1/2 mile ahead on the motorway so you don't have to change speed

on my passat i've found that cruise control uses more fuel on the motorway as it's not intelligent ie it doesn't see changes in the grade of the road so doesn't pre-empt hills. I get 3-4 more mpg if i leave cruise control off (it's a 1.9 PD130 though)

What I like about the Golf is that you can hammer it a bit and still get decent mpg

Hi, yeah I have a power/torque graph for my car and peak torque is from 2000-2900rpm, with it starting to climb sharply from 1600rpm, with peak power at 3600rpm, so I try and keep the car within the 1600-3000rpm range generally, going up to 3600rpm when overtaking.

I have tried accelerating really slowly and it is worse for MPG than accelerating fairly quickly then tickling the pedal once up to speed.

I suppose it is slightly different for each car, though I have heard how it isnt good for modern diesels to never be revved, leading to a build-up of too many sooty deposits, especially if the car has a DPF, so opening up the engine once warmed up should do them some good IMO.

Good topic. 🙂

I suppose it is slightly different for each car

Depends on the engine really. The fabled VW PD engine is the one with a massive slug of torque early on and then nothing in the high range, and it's been used in loads of cars for many years. Common Rail engines are much more like a small turbo petrol as in they take off well but keep pulling up to the line. This is because in a PD engine the injectors are actuated by the camshaft which only allows limited variation in injection timing.. whereas common rail has total control and can advance it a lot at higher revs.

I have tried accelerating really slowly and it is worse for MPG than accelerating fairly quickly then tickling the pedal once up to speed.

This is true, especially in my Prius or any other car with a CVT, particularly petrol, because by accelerating at middle ish throttle your revs are in the most efficient band ie about 3-3.5k (for petrol).

im pretty sure you already new the answer to the original post when you started the topic…you just wanted to brag about your diesel which every1 already has…

😯

I presume that was some kind of joke. If not, then thanks for your input. I have actually learnt some stuff from this thread (especially about you)

on my passat i've found that cruise control uses more fuel on the motorway as it's not intelligent ie it doesn't see changes in the grade of the road so doesn't pre-empt hills. I get 3-4 more mpg if i leave cruise control off (it's a 1.9 PD130 though)

Same here. I can build my MPG up to about 50+ but as soon as I switch to CC it starts dropping.

Weird I thought diesels did more (depending how heavy your lead foot is) but I'm getting 40+mpg out a 2 litre petrol car?

(Getting bugger all in city driving 25mpg?)

Though that van thread has been giving me ideas for a diesel next.

Weird I thought diesels did more (depending how heavy your lead foot is) but I'm getting 40+mpg out a 2 litre petrol car?

(Getting bugger all in city driving 25mpg?)

diesels get 40mpg+ in the city as well