Author Topic: M42 Heater thermostat, when was it added? (Read 2986 times)

benhanson · « **on:** May 21, 2007, 01:17:18 PM »

I'm swapping in a used engine which I had freighted up from California(I'm in Alaska). My car is a 1990 318i, the yard I purchased the engine from said it is from a 91 318i. So far, the motor looks identical with one small exception. At the heater core hookup, this motor has an extra thermostat on one hose and an extra T that feeds a small hose to said thermostat. I'm just curious if anyone knows what models had this extra thermostat? Real OEM shows a picture of it:

http://www.realoem.com/bmw/showparts.do?model=AJ93&mospid=47318&btnr=64_0135&hg=64&fg=99

but doesn't list part numbers, as it says it isn't installed in my model. Part 9 is the hose I'm looking to purchase and thus need a part number for. Part 8 is the additional thermostat.

gearheadE30 · « **Reply #1 on:** May 21, 2007, 04:42:50 PM »

Does your car have an M40 or M42? The M42 housing doesn't really look like this, although I may just be smoking something

. I can't find that particular part on my car, though.

BTW the M42 has a wide valve cover with 2 "humps" as opposed to the M40's one.

benhanson · « **Reply #2 on:** May 21, 2007, 06:48:30 PM »

It's an m42. This stuff hangs off the back, tying into the hose that exits the head. Again, it wasn't present on my original engine, which was stock from 1990. What housing are you speaking of?

dlmrun2002 · « **Reply #3 on:** May 21, 2007, 07:43:08 PM »

I think that is a heater check valve in case the heater core blows. BMW got sued by someone who got burned when their heater core blew and leaked all the fluid from the cooling system. Now if I can find my coolant leaking under manifold..... BEEEEEEETCH..
DLM

mbtech0 · « **Reply #4 on:** May 21, 2007, 08:09:48 PM »

Yes, it is an overpressure valve designed to protect the heater core. These were installed during a recall around 1993-4, I recall. They suck to install when the engine is in the car. I recall that only the E30 M42 got these. I never had to do one, as we only had a few M42 cars out there......Come to think of it, I'm not sure mine has one. I can't comment on whether you really need this, or not.

Alpine003 · « **Reply #5 on:** May 21, 2007, 11:43:12 PM »

All US m42 should have one but some owners do a bypass on this if the valve is faulty or if they suspect the valve of causing heating issues by taking it out all together. I recently replaced one trying to diagnose a heating problem. It is sort of a pain to get to but still doable if you ever have to install one or replace one.