OEM composite thermostat housing on my 97 528 is leaking yet again

[geargrinder]

Yeah, those seals will take a set over time so they seem shorter than they are supposed to be. Who knows about the URO seal. Honestly it's not that high-spec a seal in the scheme of things. Only retains coolant, isn't massive pressure... truly a 'garden variety' seal should be OK for nearly ever but never underestimate the ability of cheapo parts to surprise you! I have bought a few Uro things are were surprisingly decent I have to say. Generally for my cars its a "no go" but I've bought there stuff for certain "just need a cheap part" needs and "experimentation" purposes.

[Ed CT]

I am now an Aluminum convert, I no longer advocate OEM Plastic housing having gone through 3 of them in the last 10 years. Hopefully this Aluminum thingy is the last Tstat housing I ever need...

Yup, that's about my average, too. I've replaced mine 5 times since I've owned the car, which is about 20000 miles per t-stat housing or every 4 years.
CNN - did you heat up the AL housing prior to sanding the surface? Kind of curious to see if there are any stresses in the material that warp it when it gets to temperature. I may go with the AL housing the next time, if my rocker panel rot hasn't spread to the frame by then LOL.

[cnn]

Ed,

I had no reason to heat up the Aluminum. So far so good, it has never this bone-dry.
I am very happy with the Al tstat housing.
I will update the thread from time to time.

[cnn]

As I mentioned before, in the classic E36, BMW used all 3 seals as in the photo below:
- Black O-ring for Tstat (#6)
- Orange Seal (#8)
- Paper Gasket (#7)

I am not sure why they got rid of the paper gasket in subsequent models such as E39. Maybe paper gasket is no good for plastic housing.

Anyway, when using Al housing, I strongly believe one should use paper gasket.



E36-Tstat.jpg