VW consumption meter

Um, that's normal for consumption meters. They're just reflecting instantaneous fuel consumption, or are you suggesting that yours is doing something different from "normal" instantaneous consumption meters?

Tim

Well, quite - depending on the circumstances. If the car's being driven at a steady throttle and steady speed along a flat road, then it should be fairly steady.

Close the throttle, the ECU shuts the fuelling and the instantaneous consumption will hit maximum. Open it, and the instantaneous consumption will head towards zero rapidly.

I wonder if the OP's one of those drivers who just cannot drive on a steady throttle...?

That is exactly what is happening Tim. Is there any point in instantaneous readings?

Not on the country roads where I live no it is impossible to hold the throttle steady.

In as much as they're accurate, yes - gives an indication of how driving style, conditions etc affect fuel consumption.

You probably wouldn't find cruise control particularly useful, either, then. It's reflecting exactly what's happening with the engine's consumption. If you don't find that mode useful, don't use it...?

Why TF would you expect the instantaneous consumption figure to be anything other than, well, instantaneous consumption, which will clearly vary from bugger all when your foot's off the throttle on the overrun to a lot when it's hard down?

Are you for real , just inordinately hard of thinking or is this some sort of bizarre troll?

I found it interesting:

Vectra diesel: driving on a motorway, level ground, holding 70mph: instantaneous reading about 55mpg. Turn on aircon - mpg drops to about

Leave it on, and watch the aircon compressor cut in and out. Or open the window, and watch the aerodynamic hit.

Thanks for the comments. I'm going away for the weekend so hopefully I will be able to try it out on open road.

Some years ago I had a car with a vacuum gauge fitted which seemed to do much the same job.

Yep, but much slower to react and much less accurate.

I've only had 3 cars with a/c: this Vectra, a Vauxhall Corsa, and a Toyota Avensis.

On all 3 the a/c compressor runs continuously when switched on, irrespective of any temperatures.

The Avensis had an automatic cabin temperature control which varied the blend of cold and warm air; the Vauxhalls require a manual setting to set the cold/warm blend. This does seem uneconomic, and a system which ran the compressor only when needed would seem to be better.

As an aside, I ran the Avensis for 8 years and the a/c worked perfectly the whole time.

The Corsa is now about 8 years old and its a/c has been recharged about

The Vectra is secondhand and had a leak in the a/c radiator when I got it. Now the replacement leaks at the joints - it's going back to the a/c techician when he returns from his holiday.

I would use it to learn what driving style costs me most of my fuel consumption, but I have a good idea already by using the ongoing consumption figure.

My air con made little difference to mpg, - until I had it re-charged. :-)

I have a car with a vacuum gauge, and it reacts faster than any computer-driven consumption gauges I have ever seen. It depends on the damping applied to the needle.

Probably the cooling was better after recharging also ...

You have equipped yourself with a living room on 4 wheels and now you drive it like a hot hatch.

They are toys to play games with. The usual challenge is how steady you can drive how high you can get and maintain the average. The inverse challenge is keeping average as low as possible but there are few competitors as it costs to compete.

The instantaneous fuel consumption is telling you to drive more sedately with constant throttle. It will respond by giving better mpg overall - you will see the average increase over time. Driving it how you are you will see it fall.

Well, it shows you how much difference imperceptible gradients, bends and road surface changes make to the fuel consumption. It may also tell you if the ecu is still using fuel when your foot is off the accelerator.

I remember the old Mk3 Escort Economy (or somesuch label) had three 'Economy' lights on the sash, Red, Amber and Green. I think they were just connected to the inlet manifold with a (negative) pressure sensor and also reacted instantly (be it hitting a slight headwind, going up an incline or pressing the throttle a bit more).

It was very difficult to keep it entirely in the green and if you did you would probably get done for obstruction. ;-)

Cheers, T i m