Gauge on jeep showing hot

[Big Matt]

I just picked up an 81 CJ7 with a 6cyl and the gauge keeps registering hot. I have changed the complete cooling system including the heater core. When on the highway it gets up to the end of line before the H on the gauge driving around on the streets it stays about half- way. I check the temp with a temperature gun and it never shows to get up over 175 except the intake manifold near the sending unit. The radiator never gets up over 135 and thermostat housing gets to about 160. What do y'all think it could be? Y'all think it could still need to be flushed to try and remove more of rust? Thanks in advance.

 

[mtnwhlr]

I would think you have a bad sending unit.

 

[kryptonitecj8]

Try burping the cooling system. Since you opened it up I would bet its trapped air in the system causing local hot spots. Try parking it nose up on an incline with the radiator cap off and let it warm up untilled the thermostat opens and the water starts to circlate. You should see air bubbles rise out of the Rad.

 

[IOPort51]

Pull the sending unit, it is the best place to "burp" the water jacket, just to see if there is coolant under it. I think the smart money is on the bad/wrong sending unit.

 

[BlueBeast]

Try burping the cooling system. Since you opened it up I would bet its trapped air in the system causing local hot spots. Try parking it nose up on an incline with the radiator cap off and let it warm up untilled the thermostat opens and the water starts to circlate. You should see air bubbles rise out of the Rad.

Very useful tip! thanks a mil!

 

[CJ]

It's almost impossible to trap air in a CJ water system as the radiator cap is the highest part of the cooling system. My bet is on a bad sender or gauge. Can you test with a mechanical gauge?

 

[Big Matt]

I have already tried to get it to burp but water flow is good. I'm going to change valve cover on it and when I do I'll try no sending unit. If that don't work I'll try mechanical, never thought of that one. Thanks for all the input. I'll let y'all know how it turns out.

 

[Big Matt]

Well I put in a new sending unit and it seems to be reading good now. I took it for a nice long ride today and it stayed about half way on gauge. Thanks for all the info.

 

[mtnwhlr]

Glad to here you got it fixed. Happy Jeeping

 

[MN CJ7]

FURTHER caution is the CJ and Full size use a different gauge and sender. I went thru about 15 years of Jeep Field Service Manuals, FSMs, and they do list the resistance ranges and have pictures / drawings of the gauge face. The 1" and 2" gauges do have different faces and have different electrical ranges for operation. I would measure the oil pressure / TEMP sender pres/resistance range before installing any so they can be returned if not working correctly.



TEMP SENDERS are a issue.
I purched 3-4 inexpensive units and the temp/reistance range was not correct. I ordered Napa's premium unit, ,Elchin? Brand, double the price, and boiled it in water prior to install to test, can also be returned as new if does not pass test, and the boil waster is 212 Deg F or very close and will have a resistance value about 35 ohms. Take it out of boiling water FAST put on paper towel, something that is not a heat sink, and measure the resistance with a multimeter. This needs to be done FAST you will see the resistance change in seconds. Thought I would throw this into the conversation about CJ gauge solutions.

My Temp gauge was bairly reading with PO set up. That temp sender and 3-4 more all failed till I tried the Napa Elchin premium version for the CJ Temp Sender. That one measured correctly.

I have seen the pressure and temp issues dozens of times.

Hope that helps.