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'72 Opel GT (Sara)
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Discussion Starter · #1 · (Edited)
I decided to swap out my 160 degree thermostat for a 180 degree today. When I went to put everything back together, I noticed that the thermostat housing bolt hole closest to the engine valve cover is "slightly" stripped. I say "slightly" because it can be snugged up to where it cannot be moved by hand but not tight enough to keep a tiny bit of coolant from weeping out around the gasket at that end of the housing when the engine is running. The other side is fine BTW and can be tightened down nicely. Is using a heli-coil or perma-coil to renew the bolt hole the best solution or is there some other way of fixing this problem?

Thanks,

Matt

P.S. I know several folks I could call with this question but believe it or not a search turned up nothing! So, I thought I would start a thread for future reference - surely someone else has had this problem and will again...
 

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You are referring to the bolt that is received by the lower part of the thermostat housing correct? If I remember correctly that area is clear beneath it so you can drill the hole in the housing larger and use a bolt and capture it with a nut on the other side. This would give the best security down the road; though if you don't like that method too much the only real solution for a professional fix would be a heli-coil or weld it closed; drill, and retap.
 
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Non Civilian
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heli-coil it, it's an easy fix
 
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To expand upon what the others have (correctly) said, I helicoil all the lower thermostat housings I use because this is a very common issue.

For racing vehicles (or anything else that might have frequent disassembly/reassembly), I will helicoil the holes, then install stainless steel studs in the lower housing. So to secure the upper housing you need only fit washers and nuts. This way the threads in the lower housing stop getting abused altogether.
 
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'72 Opel GT (Sara)
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2,119 Posts
Discussion Starter · #5 ·
Thanks all for the great (and quick) replies. I'll give the heli-coil approach a shot tomorrow and may go the extra step as Bob suggests and go with the stainless steel studs.

Matt
 

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Opeler
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Thanks all for the great (and quick) replies. I'll give the heli-coil approach a shot tomorrow and may go the extra step as Bob suggests and go with the stainless steel studs.

Matt
Add anti-seize compound to the bolt installed into Heli-Coil thread insert.
I would install studs as suggested.

"The use of an anti-seize product is an excellent method of preventing galvanic corrosion, especially in hot, acidic, or caustic environments.
Anti-seize resists galvanic attack by sacrificing the metals in the anti-seize in preference to the metal parts under protection. Use on threaded fasteners to prevent rust and seizing."
 

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'72 Opel GT (Sara)
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2,119 Posts
Discussion Starter · #8 ·
Add anti-seize compound to the bolt installed into Heli-Coil thread insert.
I would install studs as suggested.

"The use of an anti-seize product is an excellent method of preventing galvanic corrosion, especially in hot, acidic, or caustic environments.
Anti-seize resists galvanic attack by sacrificing the metals in the anti-seize in preference to the metal parts under protection. Use on threaded fasteners to prevent rust and seizing."
I see that Heli-coil recommends this as well in their application catalog. Note that page 13 of this catalog has the metric insert size chart to match the correct insert for your application.
 

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'72 Opel GT (Sara)
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2,119 Posts
Discussion Starter · #9 ·
I decided to go with Bob's suggestion and install stainless steel studs. Everything seems to be leak-free now :veryhappy. Note that the Help! section of Pep Boys has a "GM Water Pump" stud kit which happens to include four 8mm x 1.25mm studs, nuts, and lock washers. I made sure to apply the anti-seize compound as Lindsay pointed out. Posting a few pix for others that may want to go this route...
 

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Trouble Maker
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I'm glad that yall have come up with a VERY good solution to the problem but I would have thought that the obvious solution would have been just to use another lower Thermostat housing. :bigok:
 

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'72 Opel GT (Sara)
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2,119 Posts
Discussion Starter · #11 ·
I'm glad that yall have come up with a VERY good solution to the problem but I would have thought that the obvious solution would have been just to use another lower Thermostat housing. :bigok:
Gene offered me one (thanks Gene!) but mine is powder- coated and I didn't want to deal with removing it and then re-powder-coating it if at all possible.
 

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Both of my thermostat housing bolts sheared off when trying to remove them. It is the reinstallation that was tricky. The bolt breaking extended a quick job into a multi-day job for me.

I thought I was clever in using a bolt extractor, but that broke off inside too. Now I had a mess, since the hardened steel bolt extractor prevented me from drilling out the bolt. I eventually was able to remove the bolt extractor and was able to successfully retap one hole. But the other was a failure.

Household hardware Bicycle part Automotive tire Gas Gear

I didn’t know about helicoils. So,TIG welded the hole closed.
Liquid Fluid Automotive tire Grey Water

Then ground the weld back flat to flange height.
Gas Auto part Pipe Circle Concrete

Then I redrilled and tapped.

Seems like the approach above would have been a much easier way to go.
Gas Plumbing Font Circle Door

After that, I polished everything up and could not find the gasket. So I hand cut one and put it all back together.

I sure did this the hard way.

hopefully it is easy to remove the thermostat housing this weekend as I go to modify it for fuel injection by adding a sensor and reroute the heater outlet.
 

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Über Genius
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I would have just put on another thermostat housing. But I'm lazy that way.
 

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Opeler
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Both of my thermostat housing bolts sheared off when trying to remove them. It is the reinstallation that was tricky. The bolt breaking extended a quick job into a multi-day job for me.

I thought I was clever in using a bolt extractor, but that broke off inside too. Now I had a mess, since the hardened steel bolt extractor prevented me from drilling out the bolt. I eventually was able to remove the bolt extractor and was able to successfully retap one hole. But the other was a failure.

View attachment 445184
I didn’t know about helicoils. So,TIG welded the hole closed.
View attachment 445183
Then ground the weld back flat to flange height.
View attachment 445185
Then I redrilled and tapped.

Seems like the approach above would have been a much easier way to go. View attachment 445187
After that, I polished everything up and could not find the gasket. So I hand cut one and put it all back together.

I sure did this the hard way.

hopefully it is easy to remove the thermostat housing this weekend as I go to modify it for fuel injection by adding a sensor and reroute the heater outlet.
Where there is 1/4"-3/8" of bolt sticking out like you have shown in your picture, I have had success in "worrying" the bolt out using an 8"pipe wrench (vise grip pliers will work too), plumbers putty and a penetrating liquid (I like CRC Freezout).

1. Build a little dam made of plumbers putty (or modeling clay or masking tape) around the bolt and fill it with penetrant. Let it sit overnight.
2. Check to see if the penetrant in the dam is gone. If so, it has been drawn into the threads.
3. Using the wrench or pliers, apply steady, even pressure and attempt to back out the bolt stub. Stop short of tearing or breaking the bolt stub with the wrench. If it won't come out on the first try, put more penetrant in the dam and let sit overnight again. Attempt to back the bolt out again. Repeatedly use this procedure for several days and your bolt will eventually back out in one piece.

I did this on my pressure washer pump where a steel bolt had rusted and broken off in the aluminum pump housing. After 4-5 days of doing this, one day it just backed out as easy as you please with no thread damage.
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