Running hot

[TexaZ3]

Delete

[Timm]

Those symptoms are perfect for either a viscous fan failure or a lack of airflow through the radiator due to a build-up of debris between the radiators:

[TexaZ3]

Delete

[rjjablo]

I would spend the small amount of extra time and pull the radiator and look between it and the condenser.

Fan is a left hand thread, put some antiseize on it when it goes back together and then you barely need to tighten it.

Buy a BMW Fan tool, worth the $20

[TexaZ3]

Delete

[Timm]

[bdiefAZ]

This has been a great upgrade for the mechanical fan:

https://www.bimmerforums.com/forum/s...1#post30182131

Hope this helps.

[TexaZ3]

Delete

[R Shaffner]

Several thoughts/questions, in case any of these help...

Whenever an engine gets hotter at idle than when running, it's normal to question whether the fans are doing their jobs. Even new parts can fail, or just not work right out of the box. When the engine is getting hotter and idling, open the hood to see if a lot of hot air is being pulled past the radiator.

Are you saying you changed the sensors already, or that you're thinking of changing them? Of course, bad sensors, or the wrong sensors could give you odd readings. But that wouldn't explain why you see normal temps when cruising down the highway and hotter temps when sitting.

I don't know that car well. Is there any chance that the sensor wires got swapped, and that your gauge is reading the output from the radiator, instead of the engine temp?

When the engine starts to get hotter, what happens when you rev it a bit while sitting still? If the temp comes back down when reving it, then I'd wonder about your water pump, or whether something else is restricting flow at low rpm.

If you're ever worried about it overheating, when you still need to drive it, you could try turning the cabin heat on and blower on high. You could also try that just to see what happens. If it brings the temp down back down that would point to problem somewhere else, like the thermostat, pump, or radiator.

Does that car have a hidden menu to let you see what the temp says through the dash display (like the e39 does, for example)?

I've heard the cheap infrared guns work pretty well. You might try one of those, aimed at various places, to see what it says. For example, you might be able to see how hot the coolant is right as it leaves the engine. That might tell you a lot. You could also check the input and output for the radiator, and check various places on the radiator to see if it's getting hot where it should (meaning it has good flow).

Good luck!

[R Shaffner]

This has been a great upgrade for the mechanical fan:

https://www.bimmerforums.com/forum/s...1#post30182131

Hope this helps.

+1. Works great on my '02 540i.

[rjjablo]

Needs a new Radiator

[TexaZ3]

Delete

[rjjablo]

But why all of a sudden? Was running fine in 100F Texas heat over the summer, and then suddenly running hot in 65F. Radiator is a BEHR unit from 2003.

Likely a clog, BMW Radiators in general not just E31 are consumables. My E39 was on its third at 200K Miles, My Scion Xb, got the coolant changed once at 160K miles when the water pump failed. Radiator was original when I sold it at 200K Miles

[TexaZ3]

Delete

[cartoonz]

Do not get anything other than the Nissens radiator. They are the best for these cars.
The Behr rads are complete crap.
Buy the Nissens.

[TexaZ3]

Delete

[Ericks2002]

Hey I also live in Texas.

I’m thinking your issue is related to your aux fan. I had my aux fan fuse blew last summer and the car did what you’re describing. Overheating only when stopped.

My e31 and my buddies e38 do the same thing where the aux fan regularly runs on speed two at stop lights. The temp gauge never moves because it’s dampened but you can hear the fan speed up when siting.

I’m guessing your temp sensor on the radiator might need replacing or the aux fan itself. Check outside the car with the ac on and look through the grill or take the cover off in the engine bay to see if the fan is spinning at low speed. Also check when your car is starting to heat make sure it’s the aux fan you’re hearing and not the engine fan clutch engaging.

[TexaZ3]

Delete

[TexaZ3]

Delete

[rjjablo]

So I have ordered a new radiator.
How much transmission fluid is in the radiator cooler? Will a bunch leak when I undo the lines? Trying to determine how much I need to buy to replace lost fluid.

I would just buy the jug, you will need it the next time you change transmission fluid

[dragon850]

If it overheats when you push it hard you either still have air in the system or your head gasket is toast...

[TexaZ3]

Delete

[Timm]

The engine was designed to be self-bleeding - the problem is that they then stuck on a heater system that certainly isn't! If the heater system is not bled, as soon as your revs go up the air is expelled from the heater matrix straight into the water pump ready to be transported deep in the bowels of the engine.

[TexaZ3]

Delete

[dragon850]

Also, another thing to check is your fan clutch... I once had an overheating issue and I had replaced the fan clutch with new OEM Behr unit.
I was pretty much at a loss and replaced most other cooling components without any luck. Then I went back to the fan clutch, and tested it. Guess what, it was bad right out of the box! Replaced that and solved my problem!