Heater Problem

[Ross Trilsbeck]

I have a 1994-320-E36. The heater seems to work OK except at idle the air temp blowing out of the vents drops from hot to cool. When you drive away the temp goes back up to hot. Car has a new rad and water pump. Is this normal or is something not working quite right.

[Jared at Pelican Parts]

This might indicate a circulation problem... Did you replace the water pump yourself?

[Stephen 325TDS]

Ross, when this happened tp my car, it was a faulty heater control valve.

Stephen

[Tim Polzin]

I don't mean to steal this thread, but it has been a bit nippy here lately, today's high was -26C (you don't want to know F).

Although the car does warm up, it does not have the GM style, burn off the lint on the floor mats heat. Is this normal, or should I be also checking my heater control valve.

Thanks...Tim

[Jeron]

These problems have been discussed very recently.

Ross, first you should make sure there is no air in the system. Pelican has a procedure for this in some of its tech articles. Look at the one on water pump replacement.

Tim, the last person with such a complaint simply had his fresh air mixer on the dash set to cold. Does your car reach normal op temp? Does switching to recirculate change the temp?

[Tim Polzin]

Jeron:

Thanks, the mixer is set to warm. If I leave the recirculation on, the heater temp warms, but the windows fog and frost pretty quick.

In cold weather, the heater temp never feels really hot, usually only lukewarm when the temp gauge gets above the blue box. The thermostat on the engine seems to work ok, although in these extreme temps, the engine will not always get up to full operating temp. Interior temp of the car does warm to shirt sleeve temps, but takes a while.

Yesterday's High was -28C. An area a little north of us hit -45C. Definately frost on the pumpkins this morning.

Tim

[Jeron]

Tim, I dont have a lot of experience in extreeme cold but your temp gauge should reach full op temp within about 5 min. If it doesn't I would say your thermostat is stuck open and it is constantly running the coolant through the radiator. Does it seem to get warm at stop but then cool again in motion?

The temp gauge is not linear, the TDC on the gauge is about 175 to 200 but the full range is something like 140 to 240 (I'm apporximating a lot on the full range.) Once it starts moving it should swing quickly up to TDC and then stay there.

There is a test mode on OBD-II cars that will give you the hex value of the F temp. I'm sure you can find it on the web if you need it to help diagnose. Nevermind, I see you are probably OBD-I.

[Tim Polzin]

I'm pretty sure the thermostat is ok. In warmer weather (like -10C) the temp gauge quickly goes to the middle and sticks there, never varying.

In these temps, if a thermostat sticks open, I would be lucky to see the engine get up to 20C (about 70F).

It has been a long time since I had a car with an engine this small. How much heat can an engine like this produce? Could I simply be at the limits of the system? I would think at highway speed, radiation from the engine block itself would be quite significant. I remember an old Toyota I had with a 2 litre engine 30 years ago. If I didn't cover the whole front of the rad, the engine would never warm up.

Tell me again why I like living here?

Tim

[Jeron]

Like I said, I have no experience in that weather but I would think any engine should be able to at least heat the coolant within the engine to operating temp. That is why I suggested the thermostat.

Does the needle eventaully reach TDC if you are sitting still with no air flow across the radiator? If the thermostat is working then the radiator should remain cold until the thermostat is at TDC. I think the 2 common themostats used are 188F and 196F which is well within the TDC range.

Since it is a 94 model and OBD-I it may not have the idiot light like temp gauge of the OBD-II models, I cant remember if they switched the temp gauge operation with E36 or with OBD-II.

[Tim Polzin]

Originally posted by Jeron
Does the needle eventaully reach TDC if you are sitting still with no air flow across the radiator? If the thermostat is working then the radiator should remain cold until the thermostat is at TDC.

Yes, it reaches TDC both sitting and moving. Rad remains cold unless it is idling for a while in these temps. If you turn the heat on full after the temp reaches TDC, the temp gauge actually drops to near the first mark above the blue box.

Probably just the dang cold. Woo Hoo, tomorrow is warming, predicted high of -20C. Ice fishing weather.

Tim

[Antonmn]

Well, this is one of the reasons I've parked my 93 325is for the winter. It seems that no matter what I've tried, the car is just uncomfortably cold.

I would suggest a 92 deg C thermostat. But that would provide only about the amount of heat that is reported. In Minnesota, it still takes a good 20 minutes of driving to get even remotely warm, and I'm sure the cooling system is working as well as it ever did.

If I were to get onto the freeway if the engine has only run for less than 5 minutes and the air temp is below 0 de F, the temp gauge will not ever reach the middle. It will if I drive slower than highway speeds, but the engine just doens't seem to make enough heat with a 65 mph wind on it.

You guys who haven't experienced Artic cold really have no idea just how cold it really is. I've found the m20 and m42 engines to be fine with the cold, but the m50 just doesn't seem to cut it.

This year (and probably in years forward), I'm driving an old Saab 900 Turbo for the winter. FWD is very dull, but the car copes with the temps far better than the BMW does. With its heater, one could drive at -20F with just a pair of shorts!

And the doors open and close without having to be slammed!

[Jeron]

"The thermostat on the engine seems to work ok, although in these extreme temps, the engine will not always get up to full operating temp."

Sorry, I was basing my line of questioning on that statement. It seamed that if it wasn't getting to TDC then your thermo wasnt working.

If the heater seems to work in warmer temps but then diminishes in extreeme cold then I would just say it is the extreeme cold causing the problem. The only suggestion then would be to try to improve the performance.

Clean the evaprator coils and heater core to improve air flow. Change the micro filter and making sure the microfilter enclosure is sealed properly.

Get seat heaters.

Good luck

[kocio67]

You may try to remove fan, it might help a bit.

[Antonmn]

There is a gem in that second to the last post. When I first bought my e36 (in Janurary, of course), cold air poured from the heater box on the passenger side. It was my first e36 and I didn't really know about the details of the hvac box, but it had split along seam on the lower cover (facing the floor as it rose to meet the firewall).

The result was that outside air was being discharged into the passenger area by the blower without having gone through the heater core. So the passenger was subjected to high-speed, outside air!

I fixed that problem by covering the seam area with gasket sealant and proping it back into place by wedging a 20-oz plastic soda bottle between the box and the floor. No leaks!

It was then that I had noticed that someone had JB Welded what I think is the cover to the heater core on. (It looks like a core cover; it sits 90-deg from the floor and is above the evap core.)

At some point I should probably look around for a used box, but with 206,000 miles, I'll wait until more goes wrong.

[Tim Polzin]

Woo hoo, got up to -20C today. All is well.

Tim