temp gauge

[desertrat78]

So, after installing a AMC 258 i6 / 4.2l in my CJ7 and working out my timing, I am on to my gauges, which I am stumped. My temp gauge is pegged out when I turn ignition on. The jeep is not even running when its pegged out. Is it a sending unit, gauge? Or something I am missing?

 

[BusaDave9]

I assume you are talking about an electrical temp gauge and not a mechanical.
So when the jeep is off the gauge is all the way to the left. You turn on the ignition and the gauge goes all the way to the right. Then what happens when you start the engine? Does it stay pegged to the right?
Those electrical temp gauges work by measuring the resistance of a thermo-resistor (the sending unit). Did you buy the gauge and sending together? They must be used as a matched set.

 

[desertrat78]

Yes it is an electrical gauge. The gauge is the original one, and the temp sending unit just came with the engine that I acquired.
The gauge will go all the way to the right without turning the jeep over or even have the key in the ignition. When I take the fuse out it returns to the left. ( I was having trouble with all the gauges and the old wiring, I installed a termial block coming off my battery and ran individual power to each gauge with a blade fuse. other gauges are fine it is just my temp I am having trouble with.)

 

[BusaDave9]

Okay, so we have a jeep AMC 258 i6 / 4.2l and a jeep gauge. They should work together. The gauge going all the way to the right means very low resistance, or more likely a short. Do you know about the jeep this AMC 258 i6 / 4.2l came out of? Did the temp gauge work in that Jeep? I think the problem is the sending unit but before you replace it look over the wiring. The problem is either the sending unit or you have a short between the sending unit and the gauge.
Here's what you do: disconnect the sending unit. Now turn the key. If the gauge stays to the left then you need a new sending unit. If the gauge still pegs out you have a short between the sending unit and the gauge. Look over the wires to find a frayed wire that may be touching ground. If you can't find the short you could replace the entire length of wire back to the gauge.

 

[desertrat78]

awesome, by preforming that little test, it is the sending unit. I will replace it and lets see what would happen. Thanks

 

[geezerjeeper]

Not sure if all the CJ instruments were the same but on my 1980 CJ5 the source voltage for the temperature gauge is shared by the fuel gauge and is NOT the full 12vdc battery voltage. It's some kind of lower regulated voltage that's arrived at by a voltage regulator located within the fuel gauge (if I remember it correctly). I would think that if you ran a wire directly to the temperature gauge from your new teminal block which is connected to the battery you are probably supplying too much voltage and it's causing your gauge to peg. The temperature gauge should be strapped to a terminal on the fuel gauge and then directly to the sending unit which provides a resistance to ground. Of course that's how mine is wired....I can't speak for all of em.

 

[GTOgoat]

My problem is the exact opposite, my gauge pegs left when the ignition is turned to the on position... what does that mean? If high resistance equals hot reading what would cause a gauge to peg left to beyond cold?

 

[toolow]

My problem is the exact opposite, my gauge pegs left when the ignition is turned to the on position... what does that mean? If high resistance equals hot reading what would cause a gauge to peg left to beyond cold?

Mine pegs to beyong cold too. Any one know why.

Sent from my SM-G920V using Tapatalk