0Willcox Corvette

It won't work...

For one, a gauge reading low... adding resistance on the input wire will only make it read lower...

I've posted what we deem as the required inputs for the 1979 gauge below... but if you look the lower the ohms reading the higher the gauge reading. so adding ohms input on the input wire will only lower the reading further. (and you can see by the required inputs that the gauge is non leaner).

Taking the center cluster out of a 1977-1982 isn't really all that hard... but if you add resistance to the input you're just going to make the gauge read higher.. you can't take resistance out of the the wire...

This is exactly why we made the gauge resistor.

calwldlife

there be a clue

7T1vette

I think your issue is the Teflon tape you put on the sender threads. The joint between sender and engine block is the 'ground' connection to that temp system.

You can "test" this theory by rigging a simple 'bypass' wire which connects the sender body to a ground point anywhere on the engine block. If you install that [temporary] jumper wire and the gauge then starts reading correctly, Teflon tape on the threads is your problem.

7T1vette

I think your issue is the Teflon tape you put on the sender threads. The joint between sender and engine block is the 'ground' connection to that temp system.

You can "test" this theory by rigging a simple 'bypass' wire which connects the sender body to a ground point anywhere on the engine block. If you install that [temporary] wire and the gauge then starts reading correctly, Teflon tape on the threads is your problem.

With a 'helper', you can take the sender out of the head, quickly plug the hole with your thumb (or other finger...or your 'helper's' finger ), put some plumber's pipe dope on the threads and reinstall it in the head. No need to drain any antifreeze.

drwet

Thank you for that. You're partially correct. Adding a resistor will certainly work - its just a matter of how well. You have to put the resistor in parallel with the sender to reduce the resistance, not series. However, now that I know what the resistance at the sender should be I can calculate what resistor would be required to get the correct reading at 180 degrees. Unfortunately with such a low value resistor (125 ohms) my reading will be way off at both ends of the scale. In fact the gauge will hardly move from 180. It would look good, but its hardly useful. Looks like I will have to bite the bullet and order up your adjustable resistor. I realize pulling the gauge cluster is not hard, I've done it so many times I feel like I should have put it in with Dzus fasteners. Its just one of those jobs I despise.

drwet

Thanks but that was about the first thing I checked. And I didn't use Teflon tape. That's a bad idea on anything with moving parts where the little pieces of tape can break of and get caught in things. In fact its not permitted to be used on airplanes and I wouldn't use it on a car either. I use Teflon thread sealer. Its a paste, in a tube. Much safer than tape.

7T1vette

As long as it didn't cure before you installed it, you should be fine.

A little piece of wire will validate that....

drwet

So I finally got around to checking out the temperature of my new engine. Pulled out an old mechanical temperature gauge I have had since the late '70's. Put it in a pot of water and brought it to a boil. A little to my surprise it reads perfectly. Installed it on the car this morning and ran it up and down the street for about 10 minutes. Temperature stabilized at 180 degrees. Clearly my temperature issue is a problem with the sender. I've already ordered the adjustable resistor from Willcox.