The Stovebolt Site Forums The Shop Area The Electrical Bay Conductive thread lock for fan temp sending unit

Hi, guys. I'm replacing the temperature sending unit that turns my electric cooling fan on and off.

(The one that I installed in my new 350 crate engine came from my old 350 and will not turn the fan on unless you tap the sensor with a screwdriver. Kind of hard to do while you are driving, ha ha)

I ordered a new sending unit (plus a spare) and the instructions say to seat it with a "conductive" thread sealant with copper, silver or graphite in it. I have seen warnings online about using Teflon tape because it insulates and interferes with the ground and the signal. Similar warnings about using silicone products.

Have had difficulty trying to find such a product in my nearby city. Car parts places sent me to electrical supply companies who have heard of the products but don't have much use for it and don't stock it.

Any ideas?

Cheers, John

Devcon Epoxy Aluminum- - - -but you'll have to heat the sensor with a torch if you ever decide to change it. Any of the "liquid solder" products would work, but if the sensor has a pipe thread like most of them I've seen, putting any sealer at all on it is a big waste of time. That's particularly true if the sensor is brass and it's going into a cast iron cylinder head or intake.
Jerry

Thanks, Jerry. None of the electrical supply companies in the city could help me unless I ordered a bulk shipment of a conductive thread sealant used by industrial electricians… So, I went to a little corner hardware store run by a family and they had Permatex Copper anti-seize lubricant that is very thick and brushed on. Made from copper particles so should work just fine. The store sells solar power stuff.
Thanks for your advice.
John

John, let us know if it works!
Lane

OK, guys, I have good news and of course, bad news. ;-)

• First the good: I installed the new JEGS temperature sending unit using the Permatex Copper anti-seize lubricant. The radiator cooling fan now comes on when its hot and shuts off when it hits a second cooler temperature. No leaks.

• Now the bad: The sending unit I bought is supposed to turn the fan on at 195 and off at 175. According to my separate dashboard temperature gauge (with its own separate sending unit at a different engine location), the fan is coming on at about 160 and off at 150.

I borrowed a buddy's laser thermal temperature gun but not sure where exactly to aim the red dot. I tried directly at the engine block beside the dash gauge sending unit, on the big rad hose coming out of the top of the engine, on the top of the rad itself and various other locations.

I got many different temp readings, as you can imagine, but the total swing in temperature was consistently about 10 degrees between when the fan would come on and when it would go off. None of the readings I took with the laser gun was higher than about 155.

So, should I be worried and how do I tell what the temperature really is? Do new sending units sometimes give the wrong temps or work wrong?

Engine is a brand new Chevy Performance Center crate 350 HO Turnkey and it still has only about 100 miles on it.

Any ideas???

Thanks,

John
(No rush getting on the road here today. It snowed overnight!)

Automotive gauges are not scientific instruments. They are at best an estimate. The way to use them is to find what is normal for your engine and watch for abnormalities.

The temperature of the casting where the sending unit is should be the same as the water the sending unit is immersed in. That should tell you how far your gauge is off compared to a laser thermometer. It sounds like your engine is not getting up to operating temp while idling.

Sounds like the fan switch is defective to me.


A side note- To determine how well your radiator is cooling, take a laser reading at the thermostat housing and another at the bottom of the radiator. Sounds like you have no problem there but I threw it in for future reference.

Thanks, Cletis. I just posted this before I saw your great advice.

UPDATE: Talked to JEGS tech support guy and he said that my problem is that the fan switch sending unit is installed in the cylinder head near the plugs on passenger side of block.

The dash temp gauge sending unit, meanwhile, is in the Intake just below the thermostat at the top front of the engine. He said it is much hotter in the cylinder head area where the combustion is happening and that's why the sending unit is kicking the fan on and off at temperatures that look so low on the dash gauge.

GM confirmed to me that the optimum temp range of this engine is 180-200 and that I have a 180 thermostat. I was told that that range is measured up on the intake.

JEGS tech guy said I should have the fan switch sending unit also up on the intake and not in the cylinder head. My engine only has one threaded inlet up there but JEGS has an aftermarket water neck to the rad hose that has a threaded inlet. So I have ordered that: Part # 969-9468 along with a bushing adapter.

Stay tuned!

John

Yes! Problem solved, finally!

It made all of the difference putting the fan switch thermal sending unit up on the intake. Used a new Hedman water neck that had a threaded port for the sending unit. The sending unit for the dash temp gauge is right nearby.

And the conductive thread sealant Permatex Copper anti-seize did the job.

Cheers,

John