Additional Thermostat.

[ThisGuy310]

Was unable to find this part on realoem, so I am wondering whether it came on all m20 E30s.
Looking at parts online it seems that you can run without this thermostat, I could be mistaken though.

My question is, what is the purpose of this additional thermostat, and can I run without it?
I plan on replacing all of the water hoses, and to me it seems this little thermostat just adds more potential failure points.


Here is a pic. (you are looking at the flywheel side of the engine.)
Took me a while to figure out what it was, p/n is 64.118391926

[e30trooper]

its for the heater core.

[jlevie]

That is an over temperature, over pressure, protection that was retro fitted to early cars and may have been incorporated in late production. The purpose of those parts is to prevent a failure of the heater core and scalding in an engine overheat.

If you properly maintain the cooling system (new radiator, hoses, expansion tank, thermostat, water pump, fan clutch at every other timing belt change (every 100k)) the chances of a cooling system failure and overheat are minimal. And if you keep an eye on the temperature gauge and park the car immediately if the engine starts to run hot you won't run the risk of a failure of the heater core from over pressure. In which case you can pretty safely delete those parts. I'm of the properly maintain the car and operate it responsibly school and just remove that stuff.

[CarsSuck]

Agreed, all around. Jim, does the radiator cap on the overflow tank "pop-off" under high pressure? I think I recall reading the service bulletin, they also changed the cap to a lower pressure one. The thermostat was added by the lawyers. When I took it out of my car, it was clogged with crud.

[jlevie]

Agreed, all around. Jim, does the radiator cap on the overflow tank "pop-off" under high pressure? I think I recall reading the service bulletin, they also changed the cap to a lower pressure one. The thermostat was added by the lawyers. When I took it out of my car, it was clogged with crud.

Yes the cap will lift in an over pressure condition. I don't know about the cap. The only ones I know of are the 1.2bar early cap and 1.4bar late cap.

[CarsSuck]

Thanks Jim. This has been popping up a lot lately. So here are the details from the NHSTA report.

[TobyB]

Huh. I thought that t- stat kept the heater from overcooling the motor
on cold days when it wasn't working hard,
thus forcing the ecu into the warm- up map and thereby failing emissions.

How a t- stat reduces system PRESSURE by restricting only ONE HOSE is... mysterious, at best.
On top of that, it's bypassed with a little hose, so it can't POSSIBLY have
any effect on pressure in the heater core.

I have a couple of those little weasels, I'll boil one and see if it opens or closes when hot.

That'll answer this. I think the NHTSA stuff is a pile of BS. The cap, yes, even the
E36 pulled that dumb stunt. But not the t- stat.

t

[cabriodster87]

Yes, it bypasses core when water temp/pressure gets crazy high. This was one of the first issues when i purchased my 325.

[Nürburgring]

I tore into my '91 318is with an M42 this week to do the "mess under the intake" delete. I came across the "additional thermostat" which gave me some serious heartburn...I have deleted it...for now but I sure don't feel good about it as I don't want my heater core to explode and scald my lower half. Yikes. Anyone have a follow-up to this delete? See my video for further details.

https://www.youtube.com/watch?v=CXLAbQjiThA&feature=youtu.be

[modernist]

I don't want my heater core to explode

If the cooling system is bled properly and you're not overheating, it's a nonissue.

[Nürburgring]

Thank you!


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