I've recently replaced the ecm temp sender, fan switch and cold start injector switch on my V6. (Borrowing the following image from JamesBond007's post earlier this year, hope you don't mind)-

Question is, will using thread sealer affect the operation of these sensors/switches? I've used some white sealant on all these sensors, that doesn't seem to harden, which the auto parts counter guy said is sensor safe and better than teflon tape. After doing so, I noticed that the engine cooling fan does not come on after the engine has been running for a while. Also, after 5 mins of idle, seems to peg the temperature gauge past the red too, but I know it's not overheating. I'm suspecting the thread sealant is doing something here. Cold start seems fine though. If no sealer is required, what can be used instead? I'm equally afraid of coolant leaks at these sensors. Any advice would be appreciated.

I have installed aftermarket temp and oil gauges on my car with the new sensors in the engine and the manufacturers instruction recommend not to use any thread sealer because the sensor needs good contanct with the engine for the ground. I did have the temp sensor that did not want to seal so I used some sealant on the threads and then attached a ground wire to the body of the sensor and ran it to ground. The gauges work as advertised and are alot more accurate than the stock gauges.

I had the same issue when I changed the temp gauge sender and coolant temp sensor on my duke. Originally I put them in with some anti seize, and they acted the same as yours. Went back to advance and got 2 new ones, cleaned the anti seize out the holes on the block, and reinstalled the new ones without anything on the threads. Seems to have worked out better, my temp gauge no longer pegs (although it still reads hot)...

Try cleaning the senders/switches off and cleaning the threads in the block, then reinstalling them. As stated, the sensors rely on metal on metal contact with the block for ground to work correctly. It may be a pain in the arse to change them again in the future, and you may need a small breaker bar to take them out, but its not that big of a deal. Its not often that they go bad...

Edit: Forgot to mention, bleed your cooling system. When you changed them, you may (and probably) have introduced air into the system.

[This message has been edited by Xerces_Blackthorne (edited 09-02-2008).]

Thanks for the responses. I was afraid of that. I might try soldering wires to the base of these sensors and ground them.

all my sensors have been replaced. I used teflon tape, 2 wraps on each. everything works fine. the white liquid is teflon paste. also works fine. there is plenty of metla to metal contact there, they are pipe threads, which are tapered, and the further in they are threaded, the tighter the fit. the teflon is almost always forced into the voids and the metal to metal contact is not insulated.

Sounds liek you have a ground issue to the intake or the block more than a sensor issue.
the stock fan switch will not turn on until 235 degrees. (or if the a/c is on.) might also be the relay for the fan. or an air bubble if not burped properly.

I've never seen a sensor issue from using teflon tape or thread sealant on a properly tightened sensor.

They need teflon tape to seal properly. It should not cause a problem unless you put on way-way too much.

What would be considered way way too much? Is a bead forming on the top threads of the sensor as it's tightened down, way too much?

Don't use teflon tape. Most of the time it causes problems. RTV silicone sealer isn't made for this and can leak.

Most liquid sealers should work and will push out whatever excess when the part is tightened.

Do not solder on a sensor. Many of them have soldered joints inside that will fail if heated that much.

Gauge sensors can be checked with an ohm meter connected to the shall and whatever they are screwed into. If they read more than a couple ohms, you'll need to pull them and use correct sealant.

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[This message has been edited by theogre (edited 09-03-2008).]