Replaced the thermostat housing assembly this weekend on my 2009 MCS with 99,500 miles. Mine was leaking, I had tightened the three bolts but that made it leak more. I would say that it was leaking past the gasket as the gasket on the new housing is different, quite a bit larger. No sign of a crack in the plastic housing.

 

You will not see the cracks , they are very small on the old ones , but when its up to pressure it will leak. When replacing: also make sure you clean an residue off the side of the head and then tighten down . You might have residue between the gasket and the head or the gasket did not seat right. Thats my guess without looking at it.


Here is a DIY link and what to looks for.

https://www.northamericanmotoring.co...hermostat.html


Parts: https://www.northamericanmotoring.co...rmostat-6.html



That's what the gasket should look like when seated. That back big pipe should be seated all the way into the rear water pipe tube also. Double check all the connections.

Thanks and good luck.

 

Thanks! I did read the posts before starting the project, great information! It was not an easy project. So is the new gasket different (improved)?

 

The gasket looked about the same from the last one. Hard to tell as when you take off the old one the gasket is smashed down. Maybe a hair thicker. Double check and make sure its seated like the one picture about. I would double check your work. Should not leak with a whole new assembly and gasket. Make sure nothing it pressing back the thermostat housing like the rear pipe.

 

Yes indeed I checked, double and triple checked everything. I have F'ed up plenty of projects in the past and learned my lesson years ago. No leaks, engine operates at 220 to 226 degrees F after warmup.

 

Thanks much for the info, I don't doubt the housing is cracked. Was an interesting project, glad to have it done. I worked on it over a three day period. BTW I torqued the three bolts to 9 ft-lbs.

 

Good , did you clean any gunk or residue off the head where the old gasket was, sometimes dirt can get on the outside, might be in the way. Also maybe the gasket was not seated ? Also did the bolts go all the way back in ?

That's all I can think of.

 

Yes indeed I cleaned it up but not much there. The old and new gaskets were both fully seated and the bolts went all the way in by hand with a socket before final torque with my inch-lb torque wrench. I will post an interesting photo when I find out how to do so.

 

[/IMG]

 

Looks like the old one is smashed down from being seated and compressed and the new one is wider ( new ) like it should.

 

OK fair enough, glad I replaced the entire assembly. It's quite the complex piece of plastic, not surprised that it tends to crack.

 

Cheap plastic will do that and I'm not just talking about the thermostat housing, the main pump is also plastic. When will BMW learn?

 

Guess I will be prepared to replace the water pump also.

 

BMW has learned that metal pumps will chew up the block when their bearings start to go, so they appear that plastic impellers are the lesser of two evils.

 

Plastic impellers aren't the problem, it's the plastic housing. That's why even Mini now has metal water pumps with plastic impellers, the housing cracks long before the bearings fail in most instances.