1966 temperature sending unit / gauge
Ok, color me confused. The temperature gauge in my '66 goes up about 1/16th of an inch and then never budges until the engine is shut down at which time it goes back down. After reading LOTs of different posts I tested things by turning on the ignition and "shorting" the sending unit wire to the engine block. The gauge pretty much pegs out and then drops again when not grounded to the engine. The posts indicated that meant a bad sending unit (gauge and wires good because the gauge moved). I bought a new TU5 as that seemed to have the most positive comments about it in the forums. Replaced the sending unit, connected the wire, drove the car, and the gauge still does the same thing, i.e. nothing. I went back and read more posts and they indicated I should test the unit's resistance. So I connected my volt/ohm meter and read about 550 to 600 ohms at "room" temperature (about 85 degrees today) - for both the old and the new unit (which looks a lot like the old so it too may be a TU5). I then took the old unit into the house and placed it in a pan of water which I proceeded to boil. Along the line I would take out the unit and check its resistance. At the temperature went up the resistance went down - as it should - until when the water was boiling (212 degrees if I remember my science correctly) at which tine it showed virtually no resistance. So that indicates that the unit is "good". So tests show the unit, the wire, and the gauge all to be "good" - yet the gauge will not move (yes, I have used in infrared gun on the engine and have seen it registering 200+ with no gauge movement). Anyone have any suggestions on what to try next? Is it possible that the metal piece in the wiring cap for the unit isn't making good contact with the unit? Might explain why when in place it doesn't seem to work but when using a jumper wire to ground it things work. If that is the case does that mean replacing the entire wire or is there some easy way to bend the metal piece to make sure it makes contact?
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Re: 1966 temperature sending unit / gauge
Hi Roger,
Are you putting anything on the sender before installing it? It needs to be bare. I think I would experiment with a potentiometer to eliminate everything in the circuit except the sender. Check for threads by Jim Lockwood - he did some research on this. Look for articles on how to troubleshoot this problem on the web. I know they are out there.
Good luck and may the force be with you!
Joe -
Re: 1966 temperature sending unit / gauge
Roger,
My reading of your data is that the senders you've tried are good and the gauge is probably good. That being the case, only excessive resistance (a poor connection, IOW) in the path between sender and gauge will cause the gauge to read low or not at all. Consider running a temporary wire directly from sender to gauge. If the gauge then works correctly, that will confirm a poor connection being the problem.
JimComment
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Re: 1966 temperature sending unit / gauge
Joe - Not putting anything on the unit before installing it. Most posts I read indicated nothing should be on it. What confuses me is ALL pieces seem to work - just not together. Thank you for your input.Comment
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Re: 1966 temperature sending unit / gauge
Jim / Larry - I will see if I can run a temp wire and also check out the "firewall connector block" - once I locate that (I assume following the wire to the firewall will lead me to it). Thank you both for your input.Comment
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Re: 1966 temperature sending unit / gauge
Just under the master cylinder. Tabs that secure the small block can break or come loose. They get brittle with age, so use care. The connectors can corrode from age and humidity. There are two different blocks of 8 wires each.
LarryComment
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Re: 1966 temperature sending unit / gauge
An additional way to test gauge accuracy is to replace the sender with a variable resistor. Apx 105 ohm resistor value should yield approximately 180* at the gauge with Ign on. Some info and hookup photos in this post.
Pull the sender wire from the sender at the engine. Connect the resistor between ground and the sender wire. With Ign on the the gauge should read near 180*. If not, you could connect the resistor directly to the back side of the gauge sender terminal and ground(cluster case). If you get a good reading there then that bulkhead connector is likely the problem.
RichComment
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