[335okc]

i was at a local auto-x event this morning. car's running hot as usual, i popped the hood open, but i saw my fan wasn't on... wtf? is the radiator fan not supposed to be on? wouldnt the dme throw a code if it is supposed to spin but not? i got no lights no nothing.

[JamesM3M5]

If the fan faults, the engine should be in instant limp mode. On our E90 328i Grand Am car on stock ECU, if you unplugged the fan, the engine would barely accelerate - severe limp mode just from unplugging the fan, even when the engine was no where near hot.

When you say the car was "hot as usual," what was hot about it? There's no coolant temo gauge, do you have an aftermarket one to look at? Anything below 212F coolant temp will barely run the fan, AFAIK.

[335okc]

ran the car to 270 after each run. and thats when i saw radiator fan was off.

[JamesM3M5]

270 on the gauge below the tach? That's oil temp and is nothing to worry about, since that's in the pan. 270 coolant temp is enough to severely damage the engine, and you'll most likely see coolant boiling out of the cap or have a severely failed headgasket or cracked head.

[335okc]

yea 270 is the oil temp, but wouldnt you think that the radiator fan should be on to help cool down? i wonder if procede has a data channel for coolant temp?

[JamesM3M5]

Sure, 270 oil temp is hot, but the oil cooler gets no help from the radiator fan. These engines are designed to run a lot hotter than previous generations for 2 reasons: aluminum block sheds heat faster than older cast iron engines, and fuel efficiency. Hotter engine = better fuel efficiency. Just as long as the ECU determines the coolant temp going into and coming out of the radiator is OK, it will only run the fan as much / as little as needed. Everything comes under the close scrutiny of the fuel economy police on a modern car - even the amount of power it takes to run an electric fan.

[Tiago@VRSF]

The fan doesn't stay on 100% of the time, it only turns on when the car needs it to be on.

If the fan failed, you'd overheat during idle. You'd also throw codes.

[335okc]

thanks for the replies, it makes sense. i let the car idle for 5 to 10 minutes after each run and the oil temp goes down from 270 to 230 without the fan on. it was just weird how that could happen without the fan.

[vase330]

I have had a fan failure in the past. My car overheated with no warning and first sign of trouble was yellow radiator sign in the dash warning of too hot... slow down and shut off.. seconds later the radiator sign went red and instant limp mode followed. through all this oil temp never went past 245F. seems there is no real co-relation between oil temp and water temp in these cars.

[JamesM3M5]

The oil temp is more related to load/hard driving, not just running temp.

[335okc]

hm... i would think that the dme monitor fan speed. of all the things it monitor, a fan cant be too hard. is it possible to test the fan ?

[Jeff@TopGearSolutions]

If you have a Bav Tool you can test fan. But as others have said you would be throwing codes or limps.

[samchoi604]

another reason to get a BT tool..