Remove a seized water temp blank plug ?

[gary gerber]

I would appreciate some suggestions on removing the original blank water temperature plug from the head. When I had the head off this summer I intended to add a water temperature gauge to my engine, I applied release agents to the pipe threads but the plug wouldn't budge. I gave up, not wanting to have to replace the head after I butchered the job. I have been sailing without a water temperature gauge for thirty five years with no overheating problems. But I thought, why not improve engine information.
Anyone have a solution on this, I don't want to destroy the head in the effort?

[hanleyclifford]

If you have a pipe plug that won't budge (assuming this is a steel or iron plug), the worst case scenario is that you will break the plug off in the head. If this happens you will need to redrill and tap the hole. I believe the hole in question is 1/2" NPT, available at your local plumber's supply or the McMaster-Carr catalogue.