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View Poll Results: snapped off thermostat housing bolts on 616/617
Yes, this has happened to me 16 53.33%
No, I break hearts, not bolts 14 46.67%
Voters: 30. You may not vote on this poll

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  #1  
Old 08-20-2012, 08:34 AM
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poll: who has broken 616/617 thermostat housing bolts?

very disagreeable experience this weekend, on my way to this years benzfest in a borrowed 83 240, and after running hot, started to overheat. Ended up having the car towed about 60 miles back to a friends house, 140 short of where I started.

Figured Id take a look at the thermostat as a first place to start, and as usual, with zero force, two of the bolts broke off in the housing.



the thermostat itself was the problem, had physically broken as some point, and was unable to open-



However, since I broke the bolts off, I had to abandon the car, return the next day after hours in traffic, extract the bolts, and install new ones.

Since ive done this about 20 times on a dozen cars, im curios how common this is, it seems to me that im guaranteed at least one broken off thermostat housing bolt, and sometimes as many as three.



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Old 08-20-2012, 08:55 AM
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I've snapped the water pump housing bolts, same idea. Good thing I had a spare housing or it would have been a long ugly repair.
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  #3  
Old 08-20-2012, 09:22 AM
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Many times on thermostat and water pump housings.
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Old 08-20-2012, 11:06 AM
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Zero force means the bolts were already broken, before the force was applied. I have broken thermostat housing bolts, many years ago, before I started using this technique:

To break loose a bolt, I always have my left hand wrapped around the tool in a knuckle fashion, then with my right palm, strike my left knuckle with an impact blow. Since employing that technique (for many years now), I cannot remember having many broken bolts.

Strange the thermostat is broken like that. Did a rivet or weld fail due to corrosion? I can't imagine either happening since thermostats are made of stainless or some kind of brass alloy.

Quote:
Originally Posted by dropnosky View Post
......

Figured Id take a look at the thermostat as a first place to start, and as usual, with zero force, two of the bolts broke off in the housing.



the thermostat itself was the problem, had physically broken as some point, and was unable to open-



However, since I broke the bolts off, I had to abandon the car, return the next day after hours in traffic, extract the bolts, and install new ones.

Since ive done this about 20 times on a dozen cars, im curios how common this is, it seems to me that im guaranteed at least one broken off thermostat housing bolt, and sometimes as many as three.

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  #5  
Old 08-20-2012, 11:13 AM
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it was all corroded because of that booger green coolant in there
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  #6  
Old 08-20-2012, 11:20 AM
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the bolts were not broken to begin with, but by zero force, I mean a slight turn with a short 10mm wrench, way less than what was needed to actually turn the bolt in the threads. The weakest part of both bolts were in the through hole of the housing cover. They snapped off immediately with the force of three fingers.

not sure on the thermostat, it certainly seemed as if the rivet holding the sides together on the plate was completely gone, no trace of it, and it had jammed in there at an angle. Im not sure of the age of the component, but the car itself has over 350k on it.
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Old 08-20-2012, 11:28 AM
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Yep. Beeen there, done that. With those bolts, it's not the mechanic at fault.

The thermostat housing is aluminum and the bolts are carbon steel. That equation, with heat as a catalyst, leads to galvanic corrosion.

Replace the old carbon steel with XXXXXXXX to avoid similar issues in the future.

Quote:
Originally Posted by qwerty View Post
Using stainless in aluminum will cause more issues than it will prevent. Cadmium-plated steel is a far-better option.

Thanks qwerty, I stand corrected.
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Last edited by anghrist; 08-20-2012 at 11:41 AM.
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  #8  
Old 08-20-2012, 11:35 AM
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Quote:
Originally Posted by anghrist View Post

Replace the old carbon steel with stainless to avoid similar issues in the future.
Using stainless in aluminum will cause more issues than it will prevent. Cadmium-plated steel is a far-better option.
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Old 08-20-2012, 11:41 AM
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Quote:
Originally Posted by qwerty View Post
Using stainless in aluminum will cause more issues than it will prevent. Cadmium-plated steel is a far-better option.
unfortunately, I used some bolts of an unknown pedigree, being whoever had them available at 7pm on sunday night yesterday, which was the home depot.

Fortunately, they were 10mm head, and correct thread, but I don't know the strength of them, I would have preferred to find some grade 8 bolts, or grade 5, but I had to get what was there.

I was on fire to get this car back to its original owner, I had borrowed in friday night, and it had a lot of important personal paperwork and tools he needed for projects on sunday and monday. Ultimately, with endless delay and traffic, he didn't see it back until late sunday.
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Old 08-20-2012, 11:51 AM
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Quote:
Originally Posted by dropnosky View Post
I would have preferred to find some grade 8 bolts, or grade 5, but I had to get what was there.
Metric bolts do not use the same rating scale as SAE bolts.
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Old 08-20-2012, 12:02 PM
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Quote:
Originally Posted by qwerty View Post
Metric bolts do not use the same rating scale as SAE bolts.
whats the metric version of grade 8 or 5 for future reference?
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Old 08-20-2012, 12:20 PM
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  #13  
Old 08-20-2012, 01:46 PM
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Galvanic corrosion is the problem here. Chase the holes with a tap, and reinstall stainless bolts-you shouldn't have a repeat
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Old 08-20-2012, 01:57 PM
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I've broken several at the wrecking yards and the ones I removed from my own cars have been been corroded badly. So I always replace them with Galvanized 8.8 or 10.9 bolts if they are available. 8.8 is sufficient, but 10.9 equals to grade 8.



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  #15  
Old 08-20-2012, 01:58 PM
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Quote:
Originally Posted by Simpler=Better View Post
Galvanic corrosion is the problem here. Chase the holes with a tap, and reinstall stainless bolts-you shouldn't have a repeat
Take a look at an anodic index table and you will find little support for that advice. As many airplane and boat owners have learned the hard way, stainless and aluminum are a really bad combination.

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