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Discussion Starter #1
So, I got a 1966 289 and the temp gauge just isn't working. I tested before buying any parts by grounding out the wire that goes to the sender and I get full deflection on the gauge. Which, from what I've looked up that then means the gauge is most likely fine and its the sending unit. I also ruled out the constant voltage regulator since I had to get a new on of those anyways and since all my other gauges were working just fine anyways.

Having decided its probably the sending unit, I got 2 different sending units. One from a nearby parts shop (autozone or oreilly can't remember which one) and the other from CJ pony parts. Both did not work, sadly. I did read up that maybe it was bad grounding due to the teflon tape the sending units were sold with. I removed those and they both still did not work. So I moved onto just replacing the wiring in the engine bay since those were in poor condition anyways, still the temp gauge specifically is not working. Wiring to the gauges are all plugged in, does look like a rats nest in there though from the previous owner.

What's the next step that I should take? Try my luck with a 3rd sending unit (third times the charm? I guess?). You folks think my gauge is bad? I mean its moving when it's grounded.

Oh, I even changed my engine ground cable.

Any help would be nice, my current guess is maybe the intake manifold isn't grounding with the rest of the engine block? Still haven't cleaned the engine bay and maybe the gaskets between the manifold and block is preventing grounding?
 

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Somebody recently had this problem with, like, three senders in a row. I suggest finding a STANDARD MOTOR PRODUCTS #TS-24. My guess is that somebody screwed up and bought a bunch of temp senders for cars with an idiot light....
 

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An aftermarket gauge with the actual temperature displayed on it is the route I'd go, you can either get an electrical or mechanical gauge depending on which you prefer. Probably a bit more accurate than the stock ones and you can actually see what the temperature is at instead of just Cold, Normal or Hot.
 

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Discussion Starter #4
Thanks for that heads up wood, I'll try to order it again but this time with that part number.

and if that doesn't work out, I might go with your suggestion El
 

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I'd double check the wire from the sender to the gauge with an ohmmeter. Your friendly rat may have cut that wire for you. You can test your new senders by putting them in a pan of water on the stove. Connect a wire to the sender post and clamp another one to the body of the sender. Connect an ohmmeter to these 2 wires. As the temperature rises so should the resistance of the sender.
 

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Actually, the resistance should DECREASE from 73 ohms to 10.
Since the other gauges are working and grounding the wire at the sender results in full deflection then the only piece left is the sender.
Another known issue is parts houses handing out later model (1980s) gauge senders. These sending units are for the 'modern' 80s and 90s gauges and have a resistance of something like 150 ohms on the low side.
 

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Make sure you have a ground strap from the engine to the firewall too. What is the ohm reading of the sender when it is installed ?
 

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Discussion Starter #9
Just ordered myself a new sending unit, but I do have the ground strap from the engine to the firewall. I'll probably go ahead and check the current sender I got to see if the resistance changes with temperature. Thanks for that, was never actually sure how to test the sender itself.
 

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With the sending unit removed, you can heat it with a hair dryer and measure the ohms change (somewhere between 10-75 ohms). Are using any type of sealer on the sender when you install it ? It has to be well grounded to the block. Only use conductive sealer if necessary. If the sender checks OK, according to the service manual, it is a problem with voltage regulator mounted on the back of the instrument cluster.
 

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Discussion Starter #11
I have all the parts for this and was intending to do it, but the can of worms just seems to be opening for my car right now. Looks like I've got a small oil leak and I'm trying to get to the bottom of that first, I do plan on updating my situation on this eventually. Thank you everybody!
 
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