Heater not blowing hot air???

[318idol]

Hello..  My '91 318i no longer blows hot air from the heater.  Radiator coolant level is topped off (I know if it gets low it affects the heater output). No matter where you set the temperature dial on the controller, only cold air blows.  The dash engine temp gauge runs in the middle, like is should. Engine gets up to temp, but the heater still blows cold.

Do the heater control dials go out?

Thanks, Gary

[DesktopDave]

Heater control can fail, but that's rare. The electric heater valve is a more likely culprit. It can get stuck shut or the solenoid could be dead. It's easy to find - right in the middle of the heater core supply hose - just take a look under the left side of the dash.

There is also a heater bypass just in front of the firewall, added as part of a BMW recall. It looks like a small thermostat. If that little thermostat has failed, it'll route the bulk of hot coolant right back to the motor.

[keflaman]

I was going to add a quick little write-up to my profile thread, but I think this would be as good a thread as any.

With the key turned to accessories, turn the temperature control knob from the extreme anti-clockwise position and after approximately 20 degrees of rotation you should hear the heater solenoid (#16) click. If you do, start the car and let it warm up.
http://bmwfans.info/parts-catalog/E30-2-doors/USA/318is-M42/L-M/jul1990/browse/heater_and_air_conditioning/heater_radiator_blower/

Pop your hood open and look for the thermostat Dave mentioned. It's number 8 in the illustration linked below and located between the engine and firewall. As the car heats up feel the difference in heat between hoses #6 and #9.
http://bmwfans.info/parts-catalog/E30-2-doors/USA/318is-M42/L-M/jul1990/browse/heater_and_air_conditioning/additional_thermostat_water_hose/

I used an IR thermometer first on hose #6...


...and then on #9 which is the inlet to the heater core and passes through the heater valve. NOTE: I realized when posting this picture that the laser dot is actually on the outlet hose of the heater core, but the results are the same: the thermostat is stuck in position and not allowing hot coolant to pass through the core.


I removed the thermostat and proceeded with the cheapest and quickest repair option: look down into the thermostat and note the very center "circle." I used a drill bit slightly larger and drilled down into the center just past the flat surface.


In this picture you can see a slot in the brass "sleeve"...


I took a hook and worked the "sleeve" out of the bore...


Until it was all the way out...


With the thermostat reinstalled, I placed a thermometer in the center outlet and noted my starting temperature...


Nine minutes later...


Five minutes later it topped out at 50 degrees centigrade. I'd say I was successful.