rockwell5640

Purchased a '96 about a month ago with 112k miles on it. I have been slowly giving it a tune up and replacing whatever needs to be replaced. The truck was in amazing condition when I purchased it but certain parts were showing their age.

About a week ago I started replacing most of the cooling system. I started with a coolant flush, then drained again to replace the radiator, upper and lower rad hoses, temp sender, and the thermostat and thermostat housing. Refilled with fresh coolant and immediately noticed coolant seeping out of the temp sender hole. The threads in the block seemed pretty corroded so I did my best to carefully screw the new one back in. The teflon tape seemed to survive the install but it still leaks very slowly. What would be the best course of action here? I am worried about removing and rewrapping the temp sender as I do not want it to break in half in the hole.

Second, what is the temp gauge supposed to be like on these trucks? When I first got it, the temp gauge was not steady. It wouldn't overheat but it would move around rapidly. After installing all the new parts the temp gauge moves between the O and the A on the gauge. Is this normal or should it just stay in one place while driving?

BareBonesXL

Teflon tape is not actually designed to seal threads. It is meant to reduce friction so that water pipes can get torqued farther in to their holes and seal through the tapered shape of the fitting. Get a liquid pipe thread sealant.

You can get stuff that says automotive on it or just plain old industrial stuff. Rectorseal 5 works great. I went through a whole teflon tape ordeal on a water tank, trying to make it work. Rectorseal got it done in one shot. Most hardware stores carry it.


https://www.rectorseal.com/pipe-thread-sealants/

https://www.rectorseal.com/web-media...al-No5_PDS.pdf

techrep

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rockwell5640

I considered the water pump when I was ordering everything but decided against it. At least the part is cheap if it dies on me.

I went ahead and pulled the temp sensor and coated it with Reactorseal 5. Does it take any time to cure? The sensor went back in smoothly and I tightened it down all the way but I noticed there was still coolant pooling on the top of the block. It was pooling very slow so I am not sure if it was just leftover spilled when I pulled the sensor out.

BareBonesXL

Should be okay right away. Maybe you have a separate leak. I don't know the sensor you're working with so assumed it was a tapered pipe thread. Are you sure it's not a straight thread that seals with a washer?

From the Rectorseal page I linked. You're probably not even at pressure yet.

"For natural gas, air and water lines up to 2" diameter and up to 100 psi, piping systems may be placed into immediate service."

BareBonesXL

It should stay in one place. Movement often means the thermostat is stuck open.

Shagg

I really dont think the temp gauge should be moving around like you're saying it is. My truck always sits at the "n" in normal once it is warmed up, unless im in heavy traffic. another truck i have usually sits around the "m". but on both trucks, once they warm up, the needle mostly stays in the same spot.

rockwell5640

It's the temp sensor on the 302 (don't think I specified what engine) that's directly to the right of distributor on the block. It's a brass plug that came with teflon tape on it from the manufacturer but from what I can tell when i first installed it all the tape scrapped off when installing.

What are the chances a brand new thermostat would be faulty?

From what I can see without tearing more out of the truck, the leak does not seem to be coming from the heads.

raski

If you cranked on that sensor, you may have distorted it or damaged the mating hole. It does not need to be that tight and when properly tightened, 2-3 threads should still be showing. If you went beyond that, you may want to try another sensor. I never to this day had to put sealant on the threads of a sensor. Sometimes, the threads are the ground connection and by putting dope on the threads, that connection may not be reliable. With your temperature swinging like that would tell me either an air pocket, faulty aftermarket temperature sender or possibly a cheap thermostat. If I had the system apart and drained like that, I wouldn't have hesitated changing the water pump.

rockwell5640

Checked this morning and no more coolant seems to have leaked out of the temp sensor hole since yesterday evening. Will check again later and burp the system. Hopefully this is the end of this problem!