Pipe dope on my temperature sending unit. Is this okay?

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cruiser

cruiser

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Hi All: The guy who rebuilt my cylinder head installed the brass temperature sending unit into the head with what looks like white pipe dope sealer. Is this correct, or will pipe dope on the sender interfere with the signal that it sends to the temperature gauge in the dash? I thought I read somewhere that these senders should be threaded directly into the head to create a good brass-to-iron connection. My FSM doesn't address this issue. Whaddya think?
 
Easiest way to tell is to put an ohm meter on it, one probe on the body of the sensor and the other at a good ground on the engine block.
No resistance= good to go, no continuity= remove, clean off, and try again.
 
If I put any thread sealant on at all I just apply a little bit. It's tapered pipe thread and unless you leave it loose, it won't leak.
 
cruiser said:
Hi All: The guy who rebuilt my cylinder head installed the brass temperature sending unit into the head with what looks like white pipe dope sealer. Is this correct
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No. It might or might not completely block the electrical connection needed between the sender and the head, but it's not at all needed or beneficial. It's brass; it's not going to seize; number one. Number two, those are dryseal threads, designed to create a leak-free seal when assembled dry/without any other materials. Remove the sender, clean it all the way up, and reinstall it dry.
 
As the old commercial used to say, "a little dab will do you". I put a small dot on the base of the threads and spin it to distribute the thread sealer. I've been doing this for decades and have never had a problem.
 
The threads will exert so much pressure against each other that there WILL be metal on metal contact

People put dielectric grease (which is an insulator) on terminal contacts all the time and there is still metal in metal contact.
 
slantsixdan said:
Dryseal threads are not quite the same thing as NPT. Related, similar, compatible, but not the same.
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Who said anything about dryseal threads? I don't care if it's a water pipe or a natural gas line. NPT gets some thread sealant or dope pending the liquid involved, just like the temperature sender gets going into a cast water pump housing.
 
dadsbee said:
Who said anything about dryseal threads? I don't care if it's a water pipe or a natural gas line. NPT gets some thread sealant or dope pending the liquid involved, just like the temperature sender gets going into a cast water pump housing.
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I always put SOME kinda sealer on NPT threads, regardless of application. Always have.
 
There's some great sealer on the market these days.......I've used Teflon tape since I was old enough to drive.
 
NPT is typically sealed with Teflon PTFE tape they make many types for many applications
 
Professor Fate said:
Easiest way to tell is to put an ohm meter on it, one probe on the body of the sensor and the other at a good ground on the engine block.
No resistance= good to go, no continuity= remove, clean off, and try again.
Click to expand...
Okay, checked it with an Ohm meter and found zero resistance, so all is well. Thanks to all who responded!
 
Probably similar to what was used OE, though whatever remnants of that remain today have become too friable to tell. I recall using several sealants - pipe dope w/ teflon, Permatex gasket sealant (gooey ethanol based purple gunk), and teflon tape (usually thicker yellow for-gas type). All have shown no leaks and get a good ground connection so the dash temperature gage reads correctly. Hard to find exact info, but I think those temperature sensors are an RTD type, where the resistance increases with coolant temperature, perhaps using a platinum wire (or perhaps less-pricey metal). I vaguely recall the resistance values being similar to a fuel-level gage (<100 ohm), whereas modern versions are higher (~2000 ohm).
 
The dash "scale" operating range is the same for fuel, temperature and oil pressure. All 10 ohms full scale and 74 at "empty". A cold static engine temperature sender, at about 68*F room temperature, will read in the 300 to 360 ohm range and you'll know it's good.
 
Only we old guys remember the Brylcreme hair commercials, 'A little dab will do ya.'
 
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cruiser said:
Hi All: The guy who rebuilt my cylinder head installed the brass temperature sending unit into the head with what looks like white pipe dope sealer. Is this correct, or will pipe dope on the sender interfere with the signal that it sends to the temperature gauge in the dash? I thought I read somewhere that these senders should be threaded directly into the head to create a good brass-to-iron connection. My FSM doesn't address this issue. Whaddya think?
Click to expand...
What about anti-seize? I used it on my oil pressure sending unit, no problems. I attached some photo's you might find helpful or at least interesting.

Temp1.jpg


Temp2.jpg


Temp3.jpg
 
I remember seeing some writeup or video or something a while back where someone experimented with putting various amounts of teflon tap on a temp sender to see if it would affect the reading. I think he did everything from no tape to something stupid like 10+ turns where you'd barely even be able to start the threads. They all showed the same resistance, so I probably wouldn't worry about it and have always done a couple turns myself as cheap insurance.
 
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