Does a defective thermostat affect your MPG

Thermostat will be replaced soon, gauge is not going further than 10 o'clock position, never reaches 12 o'clock. Does anybody know if a defective thermostate (always fully open) affect your MPG ?

Thanks.


BMW 530i Touring 2001

I would guess yes - slightly, in that the engine does not get up to optimal operating temperature.

If your engine is cold then yes, it will use more fuel. My dad once took the thermostat out of my mums magna and just run it without one. Ran like sh1t because it was always cold and the consumption went through the roof!


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It will hurt it somewhat because thermostats keep the engine at its most efficient operating temperature. Maybe someone with some first-hand knowledge can quantify it in terms of MPG per degree of deviation.

Yes it will.

It depends on the mode of failure.

Stuck HOT: Engine overheats ---> $4-5K damage

Stuck COLD: Engine runs cold, fuel mixture is rich ---> lowering the fuel mileage.

Originally Posted by stroatenmoaker

Does anybody know if a defective thermostate (always fully open) affect your MPG ?

Unless all your driving is under five or ten minutes, I can't imagine that first five minutes of slightly cooler engine temperatures mattering all that much to your gas miles per gallon given all the other variables in the mpg equation.

BTW, do you have the high cluster?

Originally Posted by bluebee

BTW, do you have the high cluster?

Yes, I do have the high cluster

Originally Posted by stroatenmoaker

Yes, I do have the high cluster

Then, even with the averaging gauge busted, you should be able to read two different KTMP figures (from the dual temperature sensor) on your cluster as shown in my post above.

- High instrument cluster check of the cooling system temperature KTMP (1)