Day 3: Tstat housing

[andyman32]

When I drove the car to check it under pressure this morning, the thermostat housing was leaking profusely, all over the upper radiator hose, and dripping down on the shock damper sprocket and the lower belt tensioner. It was steaming because the coolant was burning off the hot parts.

I certainly did replace that O-ring around the thermostat with a new one, but I'm hesitant to bolt the housing down any harder because it's made of plastic. Any ideas? Is there something else I should do to get the housing to stop leaking?

[PhilipJCaputo]

bma has a newer thermostat housing made out of aluminium.... its been a few months since I put it in, but I want to say it was like 20-30 bucks..... it might be a few dollars more at your local stealer

after time those dumb plastic pieces just give way.....

I remember it wasn't any fun getting that housing out and putting it back thats for sure!

[Rory]

bma has a newer thermostat housing made out of aluminium.... its been a few months since I put it in, but I want to say it was like 20-30 bucks..... it might be a few dollars more at your local stealer

after time those dumb plastic pieces just give way.....

I remember it wasn't any fun getting that housing out and putting it back thats for sure!

The metal one is better, but I believe that dealers are still selling the plastic one (YMMV). I would also clean the mating surfaces, I had the same problem when I did my wifes E36 t-stat. I used a scotch brite pad to clean the metal housing on the block really well so that it was smooth. Then when you install make sure that you have put on the correct seal (M5X has two t-stat designs, one that is a cork seal around the entire t-stat and another that has two smaller ones that are rubber and fit in each channel). Use the same on that was installed before the leak. Also, tighten the bolts evenly and torque them to their specified value. Good luck.

Best,
Rory

[tim]

I got the aluminum housing for my 540i. It doesn't leak. I used a little permatex blue on the mating surface when I assembled it. You could conceivably get it off without removing the water pump, and replace it. Just drain the rad, remove the lower hose, remove the AFM boot, and you should be able to get at the mounting bolts from either above or below with a socket extender.

My guess is that somehow the o-ring got pinched. On the R&R, you may want want to put some lube on the o-ring. Also, if your t-stat has that brass bleed thingee on the top, you want to make sure that it has clearance on the t-stat housing.

[Tiger]

Remember what I was trying to tell you?

[andyman32]

Thanks guys. It is still that plastic POS. BMA has an aluminum housing for $17. Of course, I spent $25 to have it overnighted. So, I probably just paid what I would have at the stealer.

Rory - I did clean the housing really well with a scotch pad; I actually cleaned everything with warm, soapy water. The water pump is brand-new. And I know I didn't pinch the O-ring because I seated it and hand-tightened the bolts before I mounted the water pump. And, that little metal valve - I did indeed make sure to rotate that so that it has clearance in the little 'hump' for it in the housing.

I think you're right, I'm pretty sure I can get it out without removing the pump.

I think I'll tighten it down more, since I've got a new housing on order anyhow. Nothing to lose, and everything to gain!

[myblack540i]

I don't mean to sound arrogant.... is it on right? I changed my T-stat last year on my 540, what should've been a 60-90 minute job turned into a 4 hr nightmare. It kept leaking every time I put it back together and firing up the motor to test for leaks. I finally figured out I had mounted the housing upside down.

I've never told anyone that before..... gosh, I feel better.

[billb]

I think I'll tighten it down more, since I've got a new housing on order anyhow. Nothing to lose, and everything to gain!

...I overtightened the housing and cracked it on the bottom at a screwhole. You might have done that. It has a specific torque setting, and if you exceed it, especially on the old plastic, it will fracture. Now I have a nice shiny aluminum housing...

Are you in class at State, Andy? Wondering when you work?...

[PhilipJCaputo]

I don't mean to sound arrogant.... is it on right? I changed my T-stat last year on my 540, what should've been a 60-90 minute job turned into a 4 hr nightmare. It kept leaking every time I put it back together and firing up the motor to test for leaks. I finally figured out I had mounted the housing upside down.


I've never told anyone that before..... gosh, I feel better.

I didn't know there was an "upside down" but its been a few months, and I don't exactly remember much about it.... Except for it was difficult to get to the bolts. I didn't remove the pump, I didn't even remove the fan..... I did have to buy some of those u-joint type socket deals that will let you use a socket wrench at a slight angle.

[Tiger]

It is the seams on that plastic housing leaking. There isn't an upside... However, there is a notch in that housing that must match the thermostat position.