85c Thermostat opens up at 75c!

[KampfKatze]

Hi!

My name is Mikael and i live in sweden, and i own E38 and E39´s. I have read and searched on several forums about my problem for a while now with 0 results about this specific problem.
I bought a 85c thermostat fron the local BMW dealer, a 85c thermostat from an E31, snapped off the old 105c in the housing and put in the 85c.

First start with the 85c i had some overheating because of air (changed radiator), after a few bleeds it went from evertything betweeen 70-90C, more bleeding after that wich resultet in 75C according to KTMP.
I have tried extra bleeding, changed the temp sensor on the radiator, took out the thermostat again to see if something is wrong, nothing is wrong from what i can see. Disconnected the battery even to do an reset of the cars computer.
The car drives fine, dosent really comsume more fuel either, but im kinda confused whats happening.

Why is it constantly showing 75C? Have i missed something??

Kind Regards Mikael

[bmwdirtracer]

Welcome to the forum Mikael.

The correct thermostat for your car is part number 11531437526. This is a MAP controlled thermostat, meaning the computer will alter the opening to different temps. I would suggest that you use this part.It comes with the housing, which has an electrical plug for the control.

After installation, you should vacuum-fill the system to prevent air pockets.

The radiator-mounted switch/sensor just controls the electric fan; the dual temp switch on the water pump housing reports to the DME and the gauge.

Disconnecting the battery does not "reset" anything except the clock.

[KampfKatze]

Welcome to the forum Mikael.

The correct thermostat for your car is part number 11531437526. This is a MAP controlled thermostat, meaning the computer will alter the opening to different temps. I would suggest that you use this part.It comes with the housing, which has an electrical plug for the control.

After installation, you should vacuum-fill the system to prevent air pockets.

The radiator-mounted switch/sensor just controls the electric fan; the dual temp switch on the water pump housing reports to the DME and the gauge.

Disconnecting the battery does not "reset" anything except the clock.

Hi bmwdirtracer and thanks for the welcome.

I am aware of having "incorrect" thermostat in my car (and at the same time not since theese engines has a variety of different operating temp thermostats aviable) but that dosent really answer my question of why
a mechanical thermostat designed to operate at 85c gets stuck on 75c?

But ive already ordered a 105c to switch back and test.

If someone knows why this happens i would love to learn about it. Ive noticed there is 100 different opinions and views on what temperature theese engines should and would run at so im really curius about it.

Thanks for the info about the tamp readings.

Kind regards Mikael