Best thread sealant for exhaust studs into water jacket

Johnny Dart said

If you just needed a "thread sealant" than yes, the Permatex high temp is the best for that.
In regards to temperature for exhaust studs, there are absolutely no issues. This is what the product is
designed for. Besides timing covers, water pumps, thermostat housing, fuel pump, etc.

Now if you have an issue with threads not tightening, or semi stripped,or whatever you want to call it.
Thats a whole other story. Permotex is a sealant, and not a loctight. So if this is what you need to do, some sort of loctight will be in order. I wouldnt give any guarantees on this, but you can try it.
Good luck !

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Thanks, well as I mentioned the threads are all good, just a touch loose. All those other applications you mentioned are all normal engine temp areas; these studs are a lot higher temp being where they are. If the truth be known, the rated temp of 204C is a conservative one which companies do to protect themselves in the 'safe margin' and could possible go a little higher. But in a situation like mine where there is a little more space to fill between the threads, how will it seal after 15 years and thousands of heat cycles? But I will just go ahead and use the Permatex the way NH9 suggested and will sleep well.