88 thermostat housing bolt size???

[DaRealTeufel]

So my thermostat is stuck on my 88 reatta and decided to swap it out today. Pretty simple in theory to change. Slid a pan under the car, removed the top hose and let the Coolant pour into the pan. Then proceeded to "attempt" to remove the one bolt holding the housing in. Even with pb blaster soaked around the bolt and being able to break the bolt free and turn it a couple threads, it decided to stop loosening and eventually rounded the head. Couldnt exctract and destroyed the head so will have to cut out or something. But No point in removing it now until I get a replacment bolt. Does anyone know the size or part number. No luck online. Thanks!

[Padgett]

I show GM Part Numbers 24505628 and 11508040  Size M8x1.25x25.

Note it does not need to be more than finger tight. The O'ring is the seal, the bolt just holds it in place. Too many overtighten to stop a leak. It won't.

Also is steel in aluminum. Always use anti-seize.

Edited January 19, 2023 by Padgett

[Ron Walker]

Regarding rusted nuts and bolts, saw an interesting response in another forum I visit (Chevrolet SSR) on a variety of lubes used to break the rust. Since you "rounded" the head on your project, it may be too late. However, I've cut and will paste the response below. Sounds like some useful info that I have not tried myself, but maybe others have and can chime in.  Sorry for the length of the article.

Here goes: 

"From my experience in restoring antique trucks I tried most of the typically referenced penetrations sold. I found that none worked better than a concoction an old time restorer recommended. It was a 50:50 mix of automatic transmission fluid and acetone. I never had it fail me in breaking loose countless “frozen” nuts and bolts. 

"Machinist's Workshop" recently published information on various penetrating oils. The magazine reports they tested these products for "break out "torque" on rusted nuts and bolts. A subjective test was made of popular penetrating oils, with the unit of merit being the torque required to remove the nut from a "scientifically rusted" bolt.

Average torque load to loosen nut: 

No Oil used .........................516 foot pounds  

WD-40 ..................... .........238 foot pounds

PB Blaster ..........................214 foot pounds

Liquid Wrench .......................127 foot pounds

Kano Kroil ..........................106 foot pounds

ATF/Acetone mix..................... 53 foot pounds

The ATF/Acetone mix is a "home brew" mix of 50/50 automatic transmission fluid and acetone. Note this "home brew" released bolts better than any commercial product in this one particular test.  Our local machinist group mixed up a batch, and we all now use it with equally good results. Note also that Liquid Wrench is almost as good as Kroil for 20% of the price.  ATF/Acetone mix is best, but you can also use ATF and lacquer thinner in a 50/50 mix. ATF = Any type of Automatic Transmission Fluid."

[2seater]

I have used the ATF/acetone mix on and off for years, and it does work well. Relatively inexpensive and a good way to use up those odd bottles of ATF from a vehicle you no longer have. I suspect power steering fluid would work as well but have never tried that.

[Padgett]

Only factor is commercial products come in a spray can but can get a squeeze bottle for the mix.

[Ronnie]

I've used Kroil for years as a machinist with good success. It was provided by my employer so cost wasn't a consideration. Trans fluid and acetone is good, but acetone is highly flammable in enclosed spaces.