Fuel Consumption.

Yeah, I've noticed this on a few cars too, mainly in the Cavalier to Mondeo market. My completely unscientific reckoning for it is that the 1.8 model of most cars is the compromise model - hasn't got the fuel economy of the 1.6 (or diesel) nor the top end of the 2.0, but is cheaper to buy and insure than the latter without saying 'poverty spec'. At a guess the gearbox and some of the engine gubbins are shared with the larger/smaller engined models, making for less than ideal performance.

Have to agree. Hired a Vectra 1.8 once and drove it to Dover via Yorkshire from Ayrshire. Couldn't believe what it cost. Did a quick sum in my head at the petrol station and it was working out at 26 ~

27mpg on the motorway!

One exception is the Passat 1.8. I bought one for my Mum last year and found consumption wasn't much worse than my Passat 1.9TD, same age. Mind you, it didn't feel much quicker though.

You had a knackered one then- previous shape Vectra's in all petrol flavours are well known to be capable of 40+ on a motorway run at sensible speeds.

My 1.8 Focus averages between 34-36mpg in mixed driving and will easily crack 40 on a run.

Tim..

All depends on how it's being driven. Something like a 1.6 Mondeo will probably be more economical than a 1.8 Mondeo if you're just doing lots of short trips and in lots of stop-start traffic. But with foot to the floor the 1.8 will fare better on the motorway.

30mpg isn't terrible if it's done a fair bit of town work though. Stop whinging, or buy a diesel :-)

Peter

Mondeo 1.8s aren't bad on fuel in general, and Avensis 1.8s are particularly economical.

Peter

DEpends on the car its in. I've found every 2L Ford I've driven whether Pinto, Zetec, DOHC Sierra lump, has returned ~32MPG. Got around 40MPG out of a 2L Cavvy and ~37 out of both of my 2L Rovers.

I get > 30mpg out of my 1.8l car very easily, and can break 40 if I'm driving steadily.

Depends on the engine, how you drive, the weight of the car, etc.

I guess that depends on your perspective, but perhaps you've driven lots of similar cars over similar routes?

As somebody said, the 1.8 is sometimes the "mid range" four banger with a

1.6 on the lower side and the 2.0 on the upper side. It sits between them for performance and fuel consumption. More often, you get fuel consumption closer to the 2.0 when driving hard and closer to the 1.6 when being gentle.

In any event, the 1.8 in the early Laguna isn't notable for being economical but it has tall enough gearing to be. My guess would be that you're not spending all that long on the motorway?

But I thought engines were more efficient when worked hard?

More *efficient*, yes.

This means that if pootling along, you're running at 30% efficienty, getting 30mpg.

Caning the nuts off it, you're running at 40% efficiency, getting 25mpg. If it were less efficient, you may only be getting 20.

Pete.

You beat me to it!

Efficiency isn't the same as economical..

To get a car to move you need to accelerate, which generally drinks a considerable amount of fuel. If you are pootling along then you may spend say 30 seconds under light accleration before reaching an economical cruise speed. If you are 'Caning the nuts off it' then you may spend 15 seconds before reaching a cruise speed.

I was under the impression that working the engine hard used the least fuel. Somebody said a while ago that for the fuel economy cycles they probably thrash it to get the best results. I'm confused now anyway.

How, exactly? The fuel an engine burns is directly proportional to the amount of power it produces.

Clearly!

It's a complicated scenario to try to model but if we suppose that at a given cruising speed the engine requires 50% of maximum power. To accelerate to this speed we must use at least 50%. If we use 50% maximum power we'll extend the acceleration over a very big distance and over many time units, _then_ we'll be cruising. if we use 100% of the power we'll be accelerating for as short as possible over fewer time units.

The question is: is accelerating at 100% more economical over the overall distance than accelerating at a higher rate before cruising.

Once cruising the rate of power production is constant, so is it more economical to use 100% of maximum power and engine speed or is there a better compromise.

You'll find that many petrol engines can deliver a sizeable chunk of their best performance and only use around two thirds to three quarters of maximum engine speed and throttle.

Our cruise control system manages the balance between relatively decent acceleration and decent economy. It uses a maximum of around sixty percent throttle under most circumstances.

In my experience, taking it to the redline in every gear until you reach the cruising speed is less economical than a more rate of acceleration.

Did you wag physics at school?

When a mass is stationary it will take more effort to move it, once it's moving then a vehicle will use less fuel , if your assumption was correct everyone would thrash their car from standstill for better economy (not true I'm afraid) accelerate as gently as possible for best fuel efficiency, I get mid 30s mpg from a 2L turbo car.

The message from petermcmillan snipped-for-privacy@yahoo.com contains these words:

Mileage freaks - the ones who do 2500+mpg in things that look like cigars on wheels - use the coast and burn technique where they work a tiny engine (10cc or less, often) at full throttle to acheive a particular speed, then coast with the engine off until they drop to the lowest speed allowable in the competition, then accelerate again.

This works because the engines are indeed at their most efficient at full throttle, and for their particular setup this is fine.

However, in real life it just doesn't work. For one thing you'd be way over the speed limit most of the time, or you'd be thrashing along in

1st gear wasting vast amounts of energy because the engine's very wasteful at high revs.