Overheating 1995 YJ 2.5

Silb

Silb

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Dec 30, 2021
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Indianapolis
I was having issues with my YJ overheating. Overtime I have replaced the heater core, radiator, thermostat, thermostat housing, thermostat sensor, water pump, fan clutch, and the temperature sending unit. Once started the YJ pretty much overheats (according to the gauge) almost immediately. I do believe that it has burped a few times as well.

There is no coolant in the oil and the exhaust seems to be normal as well.

Any advice on what to do next?
 
If the gauge is showing signs of heat immediatley then it sounds like a grounding or some eletrical issue. The temp sending unit is a variable resistor. If the connection in the wiring is broken, or if there is no clean contact between head and sending unit then you will have high resistance which would translate to the rise in temp.

Where did you buy the sending unit?

For me that was the most confusing thing to buy because they look identical to the temp sensor for the thermostat. I saw some sensors were called sending units when they are for the thermostat housing.

There is a test you can perform on the gauge and one for the sending unit. It is in the FSM.
 
Thank you for the feedback. They do both look like one in the same. I ordered my sending unit from Rock Auto. I’ll double check the connections and I think I will purchase the OEM sending unit.

When I start the engine it doesn’t immediately go to 260 degrees, but rather a slow and continuous movement to 260.

I do need to check the engine temp with a gun or something because it doesn’t smell like it’s hot as it has in the past.
Thanks again!
 
Sounds like you have covered 95% of the system. It takes my 91 a good 10 mins of running to hit 200 and typically runs right about there. Unfortunately so many of the parts to be had these days are junk. Id definitely try shooting the thermo housing,rear of head and both hoses with that gun and see what temps you get. From personal experience I will say jeep gauges are some of the crappiest to be had. My oil gauge is a good 15 psi off, the volt meter is way off buy hey..the clock is like a Rolex still!!!
 
Perhaps the water pump you installed is not turning in the correct direction… a forward turn vs reverse turn unit. Here is an in-depth breakdown on “correct” water pump part numbers/spin direction for your model:
https://Jeep Forum/threads/waterpump-tutorial.893428/
 
Hi, I think I would use a "manual" temperature gauge with the cap off, run, let it circulate and see what the actual temperature is relative to the dash gauge. I don't trust the factory gauges, especially after an engine overhaul. My factory temp sender is finicky.
dne'

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If you have an ohm meter you can check the resistance of the sending probe and compare it to this chart. I think it's the correct chart for you.

Screenshot_20220101-144147-700.png
 
Dne007 said:
Hi, I think I would use a "manual" temperature gauge with the cap off, run, let it circulate and see what the actual temperature is relative to the dash gauge. I don't trust the factory gauges, especially after an engine overhaul. My factory temp sender is finicky.
dne'

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Click to expand...
Ditto, that’s ALWAYS my first test in a case like this. That’s why I still have my Stewart Warner manual temp and man oil psi gauges.
 
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I have not been able to resolve my issue. I have replaced the water pump, fan clutch, heater core, heater, thermostat, thermostat housing, thermostat sensor, hoses, radiator, and have gone through three different temperature sending units.

I am taking the temperature at the rear of the engine as suggested. The temperature maintains a 179-180 temp when warm.

The temperature gauge will slowly go up to about 210 and sit still when I press the gas it will continue to rise in temperature, sometimes it will go down with no rhyme or reason.

I made sure the system was burped correctly and I have tested the electrical which all seems to be fine.

The only thing I can figure is the temp sending units are not compatible with the gauge. I finally ordered a MOPAR temp sending unit and hope that this works. Otherwise I am at a complete loss unless anyone has a suggestion???
 
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To verify the accuracy of your gauge, you should use an infrared temp gun and measure the temp as close to the sending unit as possible (Thermostat housing), not at the rear of the engine.
 
Thanks for the clarification. I have taken the temp with a infrared gun next to the temp sending unit and the thermostat housing. Both temps are under 200 degrees. I just can’t get the gauge to work. Do you suggest that I install an aftermarket gauge? I was really trying to avoid this.
 
Those temps still seek high to me. Shouldnt those motors run around 160? I know the factory gauges arent all that accurate, but I've never seen either of my jeeps go over 140. Longshot, but could you just have a pinched or blocked hose?
 
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