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Discussion Starter #1
I installed a new temp sender w/teflon tape and now my guage is way off (reads hot). Later that day I was working on my friends T-bucket installing guages. The directions for his guages say not to use teflon tape on the sending unit b/c it will cause erractic readings, and that the temp sender is self-sealing. Is this applicable for all sending units?
 

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Vince,
If the Teflon tape was causing the problem, it would be the other way ... reading cold all the time.
 

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Loctite makes PST, a pipe thread sealant. It is an excellent product from my many years of experience with it. A little dab on the threads will seal every time and there will be no stray particles getting into the rest of your system. I haven't seen teflon tape in our shop in years.
 

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Discussion Starter #5
I took the unit off and removed the tape. The guage reads just under hot now, but still too hot. Before the temp would read up 1/4 of the way on the guage. And no matter how much I tighten it still dribbles at little coolant. I'm gonna have to take it back out and put tape or sealant on it.

Whats the best way to de-sensitize the sender a little? I was thinking some RTV on the probe? This is a GM unit BTW.
 

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Insulating the sensor won't help, might slow the reading down just a few seconds is all.

Is this an electric gauge sending unit or a mechanical one?

Sounds like a bad sending unit or the wrong one maybe.

Use the Permatex "form-a gasket" (on pipe threads) and it won't dribble.
 

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Discussion Starter #7
Its the factory guage setup. I got the unit from NPD. Whats strange is when I had the tape on it, it read higher. What gives?
 

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Vince,maybe if it's an electrical gauge/sender it was not grounded properly (if thats applicable to you particualr setup)to the motor with the tape on the threads.

Also,do you have the ground starps from the v/covers to firewall hooked up for proper grounding in general?

Scott
 

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Somewhere in a distant corner of my mind, I recall a thread or two about replacement senders. Believe someone typed up some testing they did on replacement senders versus original GM senders and found there was a variance in the readings. May try and do a search in Electrical and see if you can find something.
Ground straps won't fix this if you have the 12 gage wire from battery (-) to the right inside fender.
 

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If your mounting the sender in the head, it will read warmer the if it was in intake manifold closer to the T-stat housing. Could that be the hi temp reading you see???
I have seen as much as a 15*F warmer temp at the head as compared to the intake.
 

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I tested my 69/396 basically a stock setup w/4 core rad,stock fan shroud & stock clutch fan setup,180 deg high flow stat, and hiflow milodon w/pump with my new autometer mech gauge attached to the head which at the same exact time reads approx 18-20 deg higher from the head by the exhuast port than when i check the coolent temp through the filler neck in the rad.

so when i see i am running apporx 200-205 deg while crusing on a hot muggy 85-90 deg day i feel it's more realistically running @ 190-195 deg which is fine for a BBC on a hot day.

In stop & go traffic on a hot day like that it will rise to 210 after 5 mins and 220 after 10-15 mins in stop & go traffic. This is really 205 ish to 210 ish on a hot day in traffic which is not great but also not too bad for a BBC in that situation.

NOTE:I did a pre-test on the mech autometer temp gauge& my rad thermometer prior to installing the mech temp sender to insure they read approx the same as a calibration of sorts.

Scott
 

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Discussion Starter #12
Hi Guys.

No ground wire to the valve cover (maybe I should do that anyway). I do have the negative cable attached directly to the block. The old sending unit read fine anyway and no chages were made since. I'm thinking about going to Autozone and trying on of theirs (7.00), but I have to cut my original wire harness to use the Autozone one. I think I try that one (with a temp. wire hooked up) and if it works I'll just have to cut the connector off and put the spade (?) type one on.

BTW, this sender is a GM part that I got from NPD.
 
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