that is the question. i am replacing the coolant temp sensor and the fan temp switch on my 1990 2.5 should i seal the threads or leave them bare?

 

Best is teflon* pipe goop; but if you use tape, remember - the circuit for some sensors completes through the block, and you really don't want teflon* in the oil or water galleys in chunks.

That is, tape; but leave the end threads bare so that a) you get a connection if necessary, and b) there's no teflon* tape hanging off the end.

RwP

*Teflon is a copyright of Dupont for its brand of PTFE; you can use non-Dupont PTFE tape in place of it.

 

If your switch is brass it should seal pretty well. If you wrap it once with thread tape, the threads should cut through and ground out while the tape left will seal the gaps. I generally don't wrap electrical sensors, but will put a single wrap around it if it seeps.If it's a real booger to get to, I'd wrap it lightly.

 

Coolant sensors are generally pipe threads, i.e. tapered.... so, no sealer generally required.