kongse

Hi -
I have a 2008 550i (N62) with 80k miles and recently replaced the thermostat after getting the 002EF4 fault code. However, after replacement, my coolant outlet temperature fluctuates wildly between 40-50C and barely gets to 80C even after prolonged driving (as measured by the Carly iPhone app and ODBII wifi reader). Replaced t-stat again but same issue. A few months ago, I replaced transfer oil cooler, radiator fan, some hoses after finding a leak.

So I'm thinking that the thermostat is fine and maybe the coolant temp sensor is just giving wrong readings. My engine temp is a relatively steady 105C and doesn't seem to be running cool even while the coolant temp is fluctuating wildly. Also, no more fault codes since replacing the thermostat (including no faults from the water pump). Anyway, I thought this would be a good inexpensive step before digging up more issues ...

This may be a stupid question, but I want to make sure of which temp sensor to replace. RealOEM has a temp sensor on the thermostat itself (part #13621433076) as well as on the return hose under the thermostat (part #13621433077). My assumption is that the coolant temp sensor is the one on the hose, not the t-stat ... but just want to confirm. Prior threads on this subject seem to indicate that N52 owners have a temp sensor on the radiator as well ... I can't find one on my N62. Is that true?

Thanks for your help

e6t.lab.rat

You are correct, there are no temp sensor on the radiator. The temp sensor on the hose - lower side on the hose nearest the radiator tells the DME when the fan should go on based on the coolant leaving the engine.

kongse

Thanks! Just to confirm, the temp sensor on the hose is the one that generates the coolant temperature reading on the hidden menus and ODBII outputs, NOT the sensor on the thermostat itself? The reason I ask is the fan seems to be turning off/on OK but I just get strange readings on the hidden menu and ODBII ... just not sure which sensor I'm reading (and which to replace). If it's the sensor on the thermostat, then there's no use replacing since I'm on my third t-stat. But if it's on the hose, then I might try and replace.

Thanks again

e6t.lab.rat

I'm not exactly sure which sensor gives readings to the DME (I'm pretty sure both does as values for both sensors are defaulted in the computer) but if your fan is going on and off when it should be then the temp sensor on the hose should be fine. Again, this sensor only triggers the fan to go on/off when it detects values exceeding temp. If no value is sent to DME the fan will not go on and other sensors will chime in. Since you've done the t-stat already, I'd replace the fan sensor and go from there. Good luck.

Gardis

I have a 2007 530i with 75K miles on it. @ 50K miles, I had a temp warning on the idrive going to work one morning. It came and went. Brought it to the dealer, who hooked it up to the computer and saw water pump faults. After reading your post, I'm wondering if it was just the thermostat? He replaced the water pump and new thermometer. Cost me $1100 (indie but fabulous German car mechanic an d honest). That's spilt milk now, but it left a bad taste for the vehicle .

Gardis

sorry, meant to say took it to my independent mechanic, NOT dealer. I swore off the dealers once and for all here in Fairfield County CT