Engine temp

[BimmerFlyer]

Hi guys, Pete here in NW Ohio,
Started to be winter here, and it seems like my engine temps are very slow to come up to normal..As in it might take 20 miles of highway driving for it to reach normal temp.. once it reaches operating temp, it acts normal..
My question is, “is this normal?”.. would figure that outside temp would not have much effect on a thermostat controlled engine... Maybe a partially stuck open thermostat? I did notice that the viscous fan coupling was very stiff with a cold engine, so it might be TU... do you think that a “always on” fan would move enough air over the block to keep it cool?..
I did verify that the dash gauge matches the DME coolant temp, so it is not a gauge issue...
Any thoughts?
ps, this is on a 1997 740il
Pete

[Timm]

That is very likely to be a stuck thermostat, although it is worth checking the viscous fan coupling for safety sake it should have no bearing on warm up time as the radiator circuit is closed until the thermostat opens....

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[BimmerFlyer]

That is very likely to be a stuck thermostat, although it is worth checking the viscous fan coupling for safety sake it should have no bearing on warm up time as the radiator circuit is closed until the thermostat opens....

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Hi Tim, first of all a big thank you for your awesome website, I know I have used it many times researching issues.... It is probably one of the largest assets the E38 community has.

Yeah, that was my thought as well, maybe some debris or something preventing the thermostat from closing all the way, not very noticeable in the summer, but for sure in the winter..

Am I correct to assume that the top radiator hose should stay “cold” untill the thermostat opens? I was playing around with it the other day and noticed that the upper hose became warm fairly quick, way before the engine was up to operating temp..the return hose was cold, but there is that large radiator in between . This would validate the partially open thermostat...

I for sure will replace the fan coupling, It is much stiffer then my E24 coupling at simular cold temps...I didn't know if, what that fan stuck ON that it would move enough air over the block itself to have an effect on it...

Thanks
Pete

[Timm]

The top hose will become hot quite quickly due to heat conduction through the coolant from the water-pump assembly. The thermostat is on the lower hose and that shouldn't get hot until the thermostat opens.