Ever seem the factory sensors with sealant on them? It's not silicone.. It's teflon based. We're talking cooling system here, not inside a boiler...lol. And it looks much cleaner.
No sir, it's not. Not since the advent of "sensor safe" black silicone in the late 80s. Even GM used to use the liquid teflon up to about 93 or 94 and then sent out a TSB regarding.......heat degradation. I was workin on the line at Yeoman's chevrolet in Macon then and remember it well. Most sensors you buy now over the dealer counter are either bare or already have sensor safe silicone embedded in the threads.
Most of them come with silicone now. It don't matter. I aint tryin to turn it into a pissin match.....just tellin you what I've SEEN in the industry. Just seal the danged thing with sumthin. That's the important thing.