Running cold on motorway, not thermostat :/

[porka]

I guess it's possible, but it's strange that it happens at 2200 rpm, below that it stays warm, even at 2100 rpm, then if I take it to 2300 rpm it starts to cool. Back down to 2100 and it starts warming again.

Had a look at the flaps but they are not electronic so can't be that.

I had a play with the old thermostat in a pan of boiling water and it opens, then closes as the water cools so basically it was working fine. There is however also a top part to the thermostat which doesn't move with the bottom part but is spring loaded. Just curious what that part is for.

[radaddict]

Originally Posted by porka

I guess it's possible, but it's strange that it happens at 2200 rpm, below that it stays warm, even at 2100 rpm, then if I take it to 2300 rpm it starts to cool. Back down to 2100 and it starts warming again.

Had a look at the flaps but they are not electronic so can't be that.

I had a play with the old thermostat in a pan of boiling water and it opens, then closes as the water cools so basically it was working fine. There is however also a top part to the thermostat which doesn't move with the bottom part but is spring loaded. Just curious what that part is for.

Well, higher engine speed circulates coolant more quickly. Coolant circulating more quickly would have a greater cooling affect.

[porka]

I have a reply from the 5 series forum and there is another thermostat which I didn't know about.

RealOEM.com * BMW E53 X5 3.0d Expansion tank, automatic transmission

It's for the gearbox oil heat exchanger (no. 4)

RealOEM.com * BMW E53 X5 3.0d Oil-cooler pipe/heat exchanger

Hopefully this is my problem !

[porka]

Well great, a few hours faffing about to change the other thermostat and £70 later, still no joy !!

Still running cold at higher revs. What gives !!

About ready to get rid of it and get a newer one with the pano roof