Originally Posted by Overboost

Thanks Fifty! All back together and fan spins so much faster. AC blows colder and coolant temps are staying not higher than 103C. Still a little high for me so ordered a new thermostat and water pump.

Everything started to change on our trip to the Black Hills, SD when the fan clutch locked up. Temperatures are running 5C to 7C high in a traffic or idle condition.

Still chasing the obvious by replacing the locked up fan clutch and slow spinning aux fan but still haven't found nirvana. Maybe next week.

Originally Posted by Fifty150hs

Yeah, sounds like you need a new stat. I think the ideal temp is 95C. That'll give you 203F. 103C is 217F. That's definitely too high. Hope your new stat gets your temps down. Interesting though, it seems failure mode on these is usually stuck open rather than partially closed.

New pump "while you're in there"?

Originally Posted by andrewwynn

[mention]Overboost [/mention]

How does your oil temp compare? Also radiator outlet temp vs. inlet? It's strange for tstat to fail hot, but you may be onto something with the water pump. If it's impeller is worn and not pushing enough volume it will cause your symptoms but you will notice in the outlet temp being too close to the inlet temp (can be caused by any blockage including dirt in the radiator fins)

Originally Posted by Purplecty

Also, How old is your radiator? I had a friend witha. 540i who had a newer behr radiator with similar symptoms you're having and replaced the whole cooling system. It ended up being a faulty radiator. He tried to shine a flashlight through it and it was not shining through and was restricting air flow. Replaced it with another behr radiator and the temps went back to normal...

Originally Posted by Overboost

What's odd is my idle is 700 and the temp would creep up to 103C within 1 min or so sitting at a light or stopped. If I gave it a little throttle to 1000 RPM, the temps would come back immediately to normal 95C. Makes me think the pump and thermostat is my next approach now.

When I had the aux fan out yesterday, I did have a look at the radiator fins and aside from a few bugs, it looked fine.

Originally Posted by Overboost

I checked the coolant level one morning on the road before starting it and it is at the proper level. Nothing changed other than the fan clutch in Minnesota. That's where the problem started.