Thread Sealant on Temp Sender Threads

[Scott M.]

Re: Thread Sealant on Temp Sender Threads

Joe I recall reading that the Wells senders (I'm recalling the P/N was something like TU5) were pretty accurate.

[Dan D.]

Re: Thread Sealant on Temp Sender Threads

Joe, do your hot water test on both senders in the water - old one and one you will buy - and measure the ohmic value of both at the same time. That should also tell you if your old one goes open when hot. Or, better yet, hook your gauge up to both of them and see how well they track. -Dan-

[Paul B.]

Re: Thread Sealant on Temp Sender Threads

Many senders come with teflon tape already on the threads, it was explained to me that since the threads are machined, they cut through the tape to provide a ground.
Someone on this forum or one of the others measured resistance on an installed sender with and without teflon tape, absolutely no difference...
You will get a galvanic reaction if you install a brass sender in an aluminum manifold without something on the threads, it could affect the resistance especially over time, and probably issues trying to remove it down the road.

Paul

[Dick W.]

Re: Thread Sealant on Temp Sender Threads

I have used Loctite PST or the Permatex equvilent for probably 30 years and have NEVER had a problem.

[Jim D.]

Re: Thread Sealant on Temp Sender Threads

I challenge anyone to install one using teflon tape, or any other thread sealant, and NOT have it make a resistance free contact with the manifold. Like stated above, the threads will make perfect contact regardless of anything used.

[John D.]

Re: Thread Sealant on Temp Sender Threads

Joe, Since around 1990 or so I have been using Loctite 545 on the TSU's and have received no complaints. JD

[Ken A.]

Re: Thread Sealant on Temp Sender Threads

Ken,

You cannot power this if its underwater, you have to suspend it and ground it as if it was in the block - I used a metal beaker.

This is done with gauge and sender, outside on the bench. You wire it to a 12v power source ( the car battery if you like) and if it is hooked up as if in the car, this will give you confirmation over the heat range. The wiring diagram is on the web.

If you have a thermometer in that same beaker you can see how the gauge moves versus actual temperature.

So something like a monkey wrench will hold the sensor and provide a ground path with your aligator clipped on the beaker going to the battery ground. Your out lead of the gauge (green wire) goes to the top of the sender.

Your loop is now closed and you can test away, ice cubes (or snow) will drop the temperature and you can repeat.


It worked very well to show which sender was the closest at operating temperature.

Then, step by step, the leads were switched into the in-car circuitry until all but the gauge was actually in the dash.

This sounds complicated but if you understand current flow its simple: from the in connector in the dash, the ground circuit from cluster metal over to the radio, and the out lead that goes through the same cluster wire harnesses out onto the top of the engine and that subsequent ground path from intake past the motor mounts, starter ground etc. are all verified OK.

Joe - you take readings frm the base sender to the battery, if you have more than a ohm or two of resistance at operating temperature when the gage is going out, then you have a ground break from that intake area over to the neg on the battery.

Ron, thanks for the info. I normally test senders with a digital ohmeter & it works fine. We test the gauge as well. You can do a satisfactory test using body heat-no need for the flames & stoves & boiling water. Ken.

[John H.]

Re: Thread Sealant on Temp Sender Threads

I've been through this countless times (usually fixing other people's cars with temp gauge issues), and have never had TFE pipe dope (paste) have any effect at all on sender grounding/function. NPT threads are cut, not rolled, are plenty sharp, and a little pipe dope isn't going to bother them.

The problem is the sender (thermistor failing). I have a Standard ST-6 in my '67, and it's dead-nuts accurate to an I.R. gun shot (probably dumb luck).

[Joe C.]

Re: Thread Sealant on Temp Sender Threads

I've been through this countless times (usually fixing other people's cars with temp gauge issues), and have never had TFE pipe dope (paste) have any effect at all on sender grounding/function. NPT threads are cut, not rolled, are plenty sharp, and a little pipe dope isn't going to bother them.

The problem is the sender (thermistor failing). I have a Standard ST-6 in my '67, and it's dead-nuts accurate to an I.R. gun shot (probably dumb luck).

Thanks for replying John. See post #8. The sharpness of the thread crests will make no difference in whether or not the joint will shear/remove sealing material and result in contact between the mated threads. Pipe threads are cut with radiused crests and roots, which are supposed to permit full contact at the root/crest as well as the flanks for better sealing. Fastener machine threads are flat at the crest and radiused at the root, and there is no contact at the root/crest junction. All of the contact in machine threads occurs along the flanks. If the tap/die is of good quality and not worn, and a high sulfur content cutting oil is used, then galling will be minimized.

[Jack H.]

Re: Thread Sealant on Temp Sender Threads

An invitation here (use 12 VDC) to create low readings... The B+ rail of the car is NOT 12V. Once the engine starts and the charging system kicks in, the supply rail typically pumps up to the 13.8-14.5 VDC range...

[Jim L.]

Re: Thread Sealant on Temp Sender Threads

The B+ rail of the car is NOT 12V. .

Hadn't seen that term since vacuum tubes went out of fashion.

[Peter J.]

Re: Thread Sealant on Temp Sender Threads

Guys I have had teflon tape on my 66 L-79 for about 15 years and it works just fine. I found out years ago about the judging issue and have meant to remove it for year but have never got around to it.
Pete

[Clem Z.]

Re: Thread Sealant on Temp Sender Threads

Guys I have had teflon tape on my 66 L-79 for about 15 years and it works just fine. I found out years ago about the judging issue and have meant to remove it for year but have never got around to it.
Pete

it depends on how many wraps you make with the tape. i have seen people split fittings because the teflon tape reduces the friction and they just keep turning because it does not seem tight to them. i always use teflon tape on inverted flare fitting threads on carb fuel lines not for sealing but to reduce the torque needed to make the flare seal. works great on those 3 X 2 carb setups on corvettes.

[Gerard F.]

Re: PS

I normally use pipe sealant with teflon..............the white paste that looks like Elmer's glue and smells like shlt. Never had a problem until recently.

Will spend some time checking sender today.

If I have to replace, which one has proven to be the most accurate over the widest temp range? I don't care what it looks like. Wells, Standard, Niehoff, GM replacement, Lectric Limited?

Joe,

I've tried quite a few including putting my bunged up original back on the car (which still worked), and I forget which one worked the best. A got a "correct" looking one from Corvette Central which I think came from Lectric Limited and which works pretty good.

But for reliability and checking the sender unit, you should use my Italian Temperature Gauge :



Marci is still wondering where that meat thermometer is

Also if you are having trouble with the gas gauge on the 65, you can borrow my Italian Gas Gauge:



But, how does it know, Luigi?

[Domenic T.]

Re: Thread Sealant on Temp Sender Threads

For what its worth, lubricating a taper thread works fine also and You can use anti-sieze which is metalic, and especially on aluminum manifolds. A must on the water nipples.

The nipples on my aluminum 427 intake would not turn out with heat, penitrating oil you name it. After a few hours I gave it hell and cracked the boss. The indifference in metals actually bonded the aluminum and steel together and it took the threads out of the intake with the nipple besides the cracking of the boss.

The good news is that I was able to get a good weld in the hole and on the cracked off piece.

A tip on getting the texture back in the aluminum after you shape it. You turn a piece of emery cloth over and against the area to texture (I think I used 80 grit) then tap it with a hammer just hard enough to make an impression like the sand casting. I do it on motorcycle casses that I weld and its non detectable.

DOM

I agree that the threads WILL find a ground thru any sealant.