Thread sealant recommendation

[scenarioL113]

I am working on a cooling system upgrade that Tony Athens had receommended. I did it on my starboard engine last year and am doing it on the port side now before I go back in the water.
I drilled out a cast iron manifold endcap that has a 1/2 NPT threaded hole that is used as a coolant by-pass. Similar to the upgrade that the 210 5.9s should get. On the 6BT the hole for the by-pass is actually in the head and is already 3/4 npt with a 1/2 reducing bushing factory installed. (the 6BT 210 can just remove the bushing and then upgrade to 3/4 X 1" hose barb to run 1" cooling hose. 1" cooling hose is recommended by Athens.

Back to the 4BT. The 4BT uses the end cap to supply the coolant by-pass and for me to upgrade properly I drilled out the 1/2 and enlarged and tapped the 3/4 NPT threads.

It came out OK (not perfect). I can thread my fitting in and get 4 turns BUT the threads on part of it are a bit on the thin side. I dont think it will leak and there is no chance of it coming out, it is tight and plenty of thread.

I would like to use some kind of thread sealer just to be 100% that it wont leak.

Any suggestions?

I was even thinking of using JB-Weld as a pipe-dope and when it sets up whatever is left in the threads would seal...maybe? IDK

[mike ohlstein]

https://www.supplyhouse.com/Hercules-15 ... T_EALw_wcB

[Carl]

Loctite 565 300F deg
Loctite 567 Higher temp 400F deg

Permatex has similar products

[Reelcrazy]

Mega loc works good. can be removed later.

[scenarioL113]

Thanks fellas!