MPG Nosedive.

[Lonz]

I've an R56 Cooper and I've noticed over this weekend that my MPG reading has dropped significantly. Without much right-foot I'm getting around 10mpg when pulling away at a junction, on a straight, level motorway at around 70mph I'm getting a mere 35-38MPG when before it would normally be reading 55-60.

I'm on runflats, but it doesn't look like there's any problem with those. The only thing that could have really changed it, is having the air-con on a lot more, but only on the lowest setting I wouldn't have thought it would decrease that much.

Does anyone have any ideas before I take it down to the garage?

[GR33NIE]

AirCon doesn't help for sure

Not sure it should quite drop that much though

[M.O.S]

It wouldn't drop that much surely. Are your tyres properly inflated? Sounds silly, but most aren't and this can seriously affect mpg - don't rely on the indicator - its rubbish and only kicks in when you have lost 1 bar of pressure!

[Andy Wilson]

Lonz
Always go for the obvious. I would say that your on board computer is playing up and the only way that you can really check fuel consumption is fill your tank right up, drive 200 miles and then top up again and calculate the consumption.
In the meantime, check your computer, especially the odometer over a known distance and see how accurate it is.

[Lonz]

Quote: Originally Posted by Andy Wilson (original)

Lonz
Always go for the obvious. I would say that your on board computer is playing up and the only way that you can really check fuel consumption is fill your tank right up, drive 200 miles and then top up again and calculate the consumption.
In the meantime, check your computer, especially the odometer over a known distance and see how accurate it is.

Yeah that's what I'm doing now. It seems to be about dead-on at the moment, but that's with a lot of motorway driving. I'll see how it goes and check it then.

[Paul]

Agree with the manual checking, but aircon, and also hotter/colder tyres messing with your pressure may mess things around a little.

[Lonz]

Update:

When I filled it up around 2/3's the way, the range says that it was 220 miles. I now have 20 miles left after doing a mere 150 miles. This has included a LOT of motorway driving, and generally taking it easy. With the tyres appearing to be fine, would it be worth me taking it into the dealer for them to have a look at? Or are they just going to turn around and say there's nothing wrong or blame my "driving style"?

[Fin]

Have you put on weight?

[Lonz]

Quote: Originally Posted by Fin (original)

Have you put on weight?