Drastic fuel consumption

[AndyTouring]

My friend has loaned me their '91 325 auto cab which is turning out to be rather thirsty - 15mpg or less!

Idling is a bit lumpy (it has an aftermarket chip installed) but runs fine when on the move. It feels like it's running with the 'choke out'.

The temp gauge only just clears the blue sector unless it's sitting in traffic for a long time. I know this isn't necessarily a problem on the M20. The heater works fine. I don't know if this is connected to the problem.

I'm suspecting the thermostat or could it be one of the motronic sensors?

[Speedtouch]

Check the blue temperature sensor as a first port of call.

http://www.e30zone.net/e30zonewiki/inde ... emp_Sensor

[AndyTouring]

Excellent thanks.

I'll have a look at that.

[Grrrmachine]

The blue temp sensor will be overfuelling, but if the temp gauge is low then the engine may well be running too cold. If that's the case, the blue sensor is just doing it's job. Temp gauge is driven by the brown sensor, and it would be very odd if they both incorrectly thought the engine was cold.

I'd be looking at a stuck-open thermostat too.

[AndyTouring]

I'll try the thermostat first then.

Have you got part numbers for the blue & brown sensors?

[Grrrmachine]

There's no point replacing the sensors on a whim, especially the brown one. But if you want to throw your money away, the part numbers can be found on RealOEM or bmwfans.info.

[clipper]

At 15 mpg I'd say it was leaking TBH...

[bmw9818]

i get about 25mpg out of mine, best ive got is 75miles off £20,