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moving coolant temp sender

S soonerbjjMember
I'm in the process of upgrading my cooling system after a recent radiator failure. As part of my upgrade I'm moving the temp sender from it's stock position in the primary coolant tank. I purchased a new sender on Ebay for $8, so I plan to simply detach the wire from the original sender and leave that unit in place in the tank. Then I'll remove the existing plug from below the thermostat, place the new sender and attach the wire. Seems simple enough.

I found the following link helpful: Banzai Runner Pantera Thermostat Replacement

As I've gone to remove the plug I find that it is quite determined to keep it's place. I have no reason to believe the plug has been manipulated since the motor was built in 1973. I've applied penetrating oil and am letting it sit overnight. Perhaps I just need to be patient with an old, stuck bolt but I want to be sure I'm on the right track.

Below is a photo of my block. Note the plug has a square head on it. Access is difficult but I'm just able to fit a box-end wrench over top and get a good position of leverage. So far it ain't budging. Am I on the right track and just need to persist?

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bosswrenchbosswrenchMember
Sooner, that pipe plug was likely screwed tight into the block when it was hot. Some come out moderately hard, others are badly rusted in place.
First, take the alt. adjusting strap off to give yourself some wrenching room, then heat the plug end up with an oxyacetylene torch until the square is red-hot. The classic way is to then slap the end of a candle against the red-hot end to shock-cool it. Water from a spray bottle also works but is messy. Let it cool all the way to room temp and try your wrench again. Some then almost come out with fingers.
FWIW, the removed plug will fill the original hole in the water tank, but use 1 full turn of pipe tape on both the plug and the new sender before tightening them in. Too many turns of pipe tape on the new sender may electrically insulate it so it doesn't work at all. In this case, more is NOT better.
jtpanterajtpanteraMember
A less dramatic and potential alternative solution to Jack's is to use a 12 point socket with extension to clear the belts. This will enable better leverage usimg a ratchet verses a small wrench.

If it rounds off, you can always go the acetylene route if you own such a set up. Otherwise, sears sells extractors for rounded bolt hads that you may consider.

JT
S soonerbjjMember
Thank you, gentlemen. I'll have a go at it today to see if my penetrating oil helped.

I tried attaching a variety of socket and extender configurations. Even with the hose removed the nipple for the coolant hose at approximately 4 o'clock to the plug severely limited access. I was able to slide the unattached socket into place but there wasn't enough horizontal space between the plug and nipple to fit an attached socket and drive... if that makes sense.

Perhaps I just don't have the correct extender. The socket would almost need to be fixed to the wrench at a 90 degree angle to clear the limited head room. I'll have another look today.

Thanks again.
S soonerbjjMember
I'm considering alternatives should this turn into a bigger ordeal.

Is there a suitable alternative location for the sender?

I've read the concerns re: placement at the water pump. If I were to make this a temporary location, would it be an improvement over the tank?

I will likely pull the motor for a more extensive overhaul next winter and could address the stubborn plug at that time.
George PGeorge PAdmin.
Leave the sender in the tank, try to remove the plug when you pull the motor. As long as the sender is functional, there's no reason to be in a hurry.

You're probably going to need to apply heat. That plug has been rusting there for 38 years. I used to have trouble removing the plugs on the sides of the block, even when they were less than 10 years old.

-G
Last edited by George P
bosswrenchbosswrenchMember
Odd readings reportedly result when the sender is installed in a water pump heater hose boss. Possibly from cavitation bubbles. There's nothing wrong with temporarily leaving the sender in the tank, as long as you-
1)- remember the water temp reported on the gauge is probably always reading low
2)- watch the gauge's reading like a hawk, for abnormally low temps as the level drops below the sender. That's your clue to add water.

If the cooling system is completely stock, one problem is a U.S- made radiator cap is shorter than a Euro cap, and won't hold its rated prssure. Worse, water may bypass the small hose and leak out around the cap. The leaking water runs down the tank, across the inner fender and straight into one of the big holes in the lower subframe rail. Where it does what water always does in a steel enclosure...
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