No heat?

[KenC]

I've bled the radiator 3 times in my M42, but I still can't get the cooling/heating system to function properly.

I only have heat while driving above 2500rpms and the temp doesn't really stabilize (doesn't overheat or get really cold, but just fluxuates with the heater being turned on and off).

The thermostat only has about 5k miles on it, and the water pump is brand new. Could it still be a thermostat problem?

[E30nate]

did you turn the heater on when you filled the system and bled it?

[HustlinDa858]

on the back of the head pull the line off that goes to the heater core, air could be stuck there

[txleadfoot]

does it matter the orientation (top/bottom) of the heater hoses going into the firewall from the engine bay?

I'm having a similar issue: only heat at idle. Once I take off, no heat. All this on a fresh M42 rebuild. I also noticed the jumpy temp gauge levels out at halfway once I turn the temp control to heat. weird.

[FredK]

Yes. Orientation matters. A sure sign of reversed heater core hoses is when you have heat at idle, but once you hit the highway, the heat cools down significantly.

[txleadfoot]

thanks fred, i'll give that a try!

[viali8]

Yes. Orientation matters. A sure sign of reversed heater core hoses is when you have heat at idle, but once you hit the highway, the heat cools down significantly.

My brother had no heat in his 89iS. This was EXACTLY what was wrong with it. I popped the hood on my car and he popped the hood on his car and compared the hoses. Sure enough they were reversed. It was a five minute fix. Now he has heat. Thanks:D

[txleadfoot]

Thanks guys. Not a five minute repair, but fixed the issue nonetheless. Now I have heat. For some reason, the temp gauge seems less jumpy too.

[KenC]

Is the heater valve a separate piece from the inlet pipe?

[FredK]

Yes. It bolts on with 3 little bolts.

[txleadfoot]

Ken, have you found the issue yet? I wonder if you have a chunk of old plastic water pump impeller stuck somewhere...

[ron1999]

ok
so now when everyvody know's that the pipes are the other way around - can soneone please say what is the right direction?
there are two inlets on the firewall side - upper and lower one
and there are two hot fluid coming from the engine -
one coming from the head and the other one coming from the plastic thingy, right?
so which is which?


thanks


Ron.

[rThor432]

I have the same problem with my M42 (same as OP's issue). My temp needle wasnt getting out of the blue, and I had no heat so I assumed it was a bad thermostat. Took it apart and found that the t-stat wasnt visibly broken (usually I find them in bits). I installed a new t-stat anyway and bled it and now the guage gets to the midway mark like it should, but does fluctuate a bit up and down.

I have heat only when I'm moving. I havent had any time to mess with it any more.

[DCColegrove]

Another symptom of a common problem look here:

http://www.r3vlimited.com/board/showthread.php?t=125034

[txleadfoot]

Nevermind

The gauge needle kept on twitching. the grounding nut on the cluster was loose.

Thanks guys. Not a five minute repair, but fixed the issue nonetheless. Now I have heat. For some reason, the temp gauge seems less jumpy too.