'99 e46 overheat question

[Brent Seidel]

Hoping that someone may have some advice regarding the following scenario. Parked manual transmission 4dr E46 outside in freezing temps last night which I usually don't do. This morning after defrosting and driving 30mins noticed heater wasn't putting out warm air as I would expect. At this time I noticed that coolant temp gauge was pegged at the top of the red. No dummy lights! I took the chance of driving the additional 20 mins to complete my trip and inspected the engine at the end while running. Electric fan was not running. After cool down coolant level was good. Later I restarted the engine and let idle back up to operating temp. Fan did start to spin slowly as temp gauge reached 12 o'clock position, and gauge maintained 12 o'clock position. I just haven't had the chance to take the car for a drive to try and duplicate problem. I don't see a secondary fan on this car. Does this fan regulate speed based on temperature? Or does it's slower speed indicate that it is shot? Maybe something different? Thanks in advance -Brent

[Jeron]

You should have a pusher fan in the front and you primary fan (between the rad and engine) appears to be electric.

Make sure your coolant is the proper proportion of coolant to distilled water.

[Brent Seidel]

There is one large factory electric fan behind the radiator that pulls air through it. The car has always run with the temp gauge at 12 o'clock until just yesterday. I did drive the car yesterday evening and this morning and now the temp gauge is hovering at the top of the cold zone. The heater is still putting out little heat. I read in another post something about the guage not reading direct from a sensor, but going throught the computer system. Considering the complexity of the electrical system on this thing I will be interested to see what a mechanic has to say about it. Seems like if the gauge is showing hot, and then cold, the coolant level is still good, the heater is cool, and there is no indication of overheating; that it's probably an electrical issue.

[Jeron]

I was in a hurry when I made my last post.

The initial story about parking in sub freezing then running hot but no primary fan, made me think you were running too much water % and it possibly froze in the heater core and possibly the radiator. I'm not convinced that that happened but it may be possible.

I'm not sure on the 99 but I suspect the fan is two speeds and neither one is slow, they are fast and very fast. So running very slowly may indicate a bad fan. However a bad fan will not cause an overheat if you are driving 40+mph. Depending on the temperature it could take 5 -10 minutes to overheat at idle without a fan.

The gauge does not show true readings. It is TDC for about 176-206F, IIRC. A legitimate electrical problem causing you problems is unlikely, especially since it is truly running cold.

If it consistently runs cold and shows cold then it could be the thermostat.

Showing hot intermittently and no cabin heat is usually air in the system.

I would start by bleeding air from the system.

[Brent Seidel]

Dropped car off at mechanic with explanation as cited above. He immediately claimed foul on the thermostat. He explained that there is a valve that will automatically shut off flow to the heater core when temps spike to protect it from blowing out. He was surprised that I didn't get a check engine light. It'll be interesting to see what he comes up with.

[Jeron]

A failed thermostat is likely.

I was skeptical about the heater core protection valve but after some research I think he is right. I still haven't figured out how it works because there doesn't seem to be an actual secondary thermostat. Maybe it is electronic, using the heater core temp sensor then closing the heater core valve.

[Brent Seidel]

Yup, The one of the ears that holds the whole spring assembly onto the housing had popped off and was on there all cockeyed.