Uh oh... Thermostat Housing Blew Open

[ElNormo]

So I replaced my thermostat a few weeks ago when I replaced the coolant pump. Things were going well, until today when I was backing into a parking spot. When I got out, the engine had just begun to steam. Sure enough, an enormous puddle of coolant erupted under the engine.

It appears that the four bolts holding the thermostat housing sheared themselves. When I replaced the thermostat, I used the existing bolts. Could they have been weakened? I used a torque wrench so as to avoid over-torquing them. But they could have been pretty old.

It's been oppressively hot here lately, and I had the A/C running.

I'll attach a picture.

Has anyone ever heard of this happening? Advice?

Thanks,

Norman

[ElNormo]

So I replaced my thermostat a few weeks ago when I replaced the coolant pump. Things were going well, until today when I was backing into a parking spot. When I got out, the engine had just begun to steam. Sure enough, an enormous puddle of coolant erupted under the engine.

Just an update. I replaced the bolts tonight, and will refill/bleed the coolant tomorrow.

Thanks all,

Norman

[Rus]

The t-stat housing bolts tend to see a lot of corrosion and with time that can seriously weaken them. I think you got off easy this time since it was just some bolts. Good luck!

[bmwrp8]

wow! that's the first that I saw that. I just bought a new thermostat and was planning to install it tonight. ill buy new bolts first mine is an 89too with 302,000 kms. the bolts might have weaken with fatigue thru out its 20 years in service.

[BMWCCA1]

Sometimes using a torque wrench is worse then a common-sense wrench. What torque value did you use? What was the range of the wrench? When was it last calibrated?

It would seem to me you'd be hard-pressed to apply enough torque to break the bolts going in without stripping the housing threads. I suspect they were distressed from the process of taking them out. That's my guess.

Could be they weren't the correct bolts though the application doesn't call for a lot of strength. I suspect this isn't the first time the housing has been opened.

[Ross]

These do tend to corrode but usually they take out the threads in the aluminum when that happens.
My money is on overtightening. They only need to be snug.