It's been a while since I replaced a coolant temp sending unit for the gauge, I forget, do I put teflon paste on the threads to keep it from leaking or not cause I was thinking that the unit grounds itself on those threads but I can't remember.

 

The new sending unit will usually come with a dab of sealant already on the threads. If not you can add your own but don't use too much. Pipe threads technically don't need a sealer as the threads are tapered to provide a seal but a little sealant doesn't hurt. Just don't cover the entire threaded portion, one or two threads is enough. The ARP stuff works good.

 

teflon tape/paste/dope ect is actually a lubricant as well. Without it the fittings wont screw in as well or as far and will leak.

When you tighten the fitting, the sealant/lubricant wear off as it goes, only leaving some in any voids in the threads. Grounding is not an issue.

 

I put in the new sending unit with some sealer on it and now the gauge stays at 100 degrees, not an issue cause the fan still kicks on but it would be good to see the temp in case the thermostat gets stuck. Any ideas on why it isn't reading, or do Napa parts suck? Opinions needed ASAP, thanks ahead of time.