Quote Originally Posted by 40FordDeluxe View Post
It really depends on how good the threads are machined on the fittings if you get a perfect seal or not. Most always tend to leak in my experience with no sealant on the threads. I've found the liquid type sealant works best though.

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I have used RectorSeal No. 5 for years on water temperature sensors with total success. It has great sealing properties, lubricates, and remains soft so removal of a water sensor is easier. I do not believe it has any dielectric characteristics as evidenced by a continuity reading of zero ohms between the brass base of the water sensor and the aluminum manifold.