Bubbling Coolant

[VolvoAffair]

I recently completed a head gasket repair and replaced every coolant hose in the system, including a new radiator, bottle and cap. Unfortunately, I am building pressure somewhere and bubbling over at the cap. I have been unable to detect any issues with cross contamination with the oil and engine coolant.

However, I do have a coolant leak at the junction between the thermostat housing and the temperature sensor. Can this leak alone cause sufficient pressure to escape and cause the coolant to bubble over?

The expertise of this forum is much appreciated.

[RickHaleParker]

Can this leak alone cause sufficient pressure to escape and cause the coolant to bubble over?

It can. You need to fix the leak anyway, your get your answer when you do.
Did you check the head and deck for warpage when you replace the head gasket?

[VolvoAffair]

Yes, I checked the deck with a level and feeler gauge, and had the head resurfaced before installation.

The leak is a result of stripped threads––not sure if its the brass threads on the temperature sensor, or the aluminum housing itself. Either way, I was hoping to avoid having to remove the thermostat housing b/c it involves removing the power steering pump. Do you think I could simply use an aerobic epoxy to seal the stripped threads?

[SuperHerman]

Couple of items. Stripped threads are rather common on aluminum castings. Usually it is from over torquing or improper bolt length. If the bolt is too long it will bottom out and the torquing will pull the threads. Check your bolt length - someone before you may have put the wrong bolts there.

I am not a fan of fixing stripped threads with glues. It has never worked for me. If you go with an epoxy it will need to be high temperature and be able to survive many cycles of heat. Epoxy starts to fail with heat - it is one of the ways one removes it. So if you use the wrong epoxy it may hold for the short term and fail in the middle of no where.

Epoxy is not aerobic - it is cured via chemical reaction with the hardner component.

I think what you meant is "anaerobic".

"Anaerobic adhesives are also known as threadlockers or retaining compounds. They are single component liquids that solidify in the absence of oxygen, as when trapped between mated surfaces such as the threads of a nut and bolt or between concentric assemblies." (ResinLab's Cynergy®) I am not sure if common anaerobic sealant would hold up in your application as it is not generally meant to fill voids - remember it cures with the absence of air - which is essentially void free.

The best approach is to figure out where the leak is - then use a helicoil to fix it.

If you could post a picture it would help in coming up with the best solution.

[RickHaleParker]

If I was going to try a quick fix, I would try Plumber's Thread Sealing Tape first. It is easy to reverse and cleanup if it does not work, epoxies are a different story.