phxmark

I own a 2000 Cherokee with a 4.0L engine. The other day when going up a long hill on the freeway, the temperature gauge "jumped" from the normal 210 to just barley into the redline. The engine was running normal and there was no boilover. The electric fan was on, and the engine fan was also working. I had no loss of power or other signs of overheating.

I pulled over, left the engine running, and popped the hood. The fans were pulling air and the engine did not appear to be overheating. I was pulled over less than a two minutes. As soon as I got back in the jeep, the temperature gauge "jumped" back to the normal 210. I know if the engine was running hot, the temperature would creep back to normal.

I am going to flush the cooling system and then try the "air bleed" that I have seen mentioned here.

Is it possible I have an air bubble in the system or a failing gauge sening unit? Also, i have read that there a two or three sending units on this engine. Which one is for the gauge?

ReverendOD

Are you loosing any coolant? With the gauge quickly jumping like that I would suspect the sensor. Should be the one in there thermostat housing IIRC.

RENIXBEAST

X2 sounds like a sensor issue

TrekkerJmm

There are two that I know of. One is up front where the thermostat goes (this one is for the E fan) and one in the right rear top of motor near valve cover (this one is the temp sensor). I sent you a PM that may help...Tj

phxmark

Not losing any coolant.

Going to completely flush the system today, replace the sensor, refill and purge of any air.

93gc40

Change the T-stat while you are at it. Also check the mech fan clutch is really working, should be noticably tighter on the shaft when at normal temp than when cold.

phxmark

I did a chemical flush of the cooling system really good, about three times before I could get the water mostly clear. The first flush looked like mud. Even cleaned out the recovery bottle.

The temperature sensor was special order and cost $70 at Pep Boys. Will wait and see on this.

Also, replaced the radiator cap. Discovered the cap that was on there was only an 8lb cap. I bought this Cherokee used about a month ago so I do not know what the previous owners were thinking.

Put in Prestone Rust Inhibitor and Long Life anti-freeze/coolant.

Did a test drive best I could under load and the temperature gauge didn't go above 210. It was running just slightly above 210, probably about 225 before the flush.

Will see how it does next weekend on the hills.

Thanks all.

posjeepxj

if there was a bubble in the system it will read at much higher temp that the liquid. maybe it passed gas and read the bubble. all the flushing and woo haha got rid of it. my guess anyway

letsgomuddin

X3 on the sensor or possibly your gauge cluster connections, my TJ had the same gauge cluster and i had that problem often till i pulled it out and fixed it

phxmark

Took the XJ on another long drive. The temp gauge only went just below redline twice, both times up long hills. Better then when I first posted, which it did it on every hill I would go up.

I also noticed that when I switched on the heater, the air was barely lukewarm. Since the temperature sensor is in the heater supply line passage of the thermostat housing, would it be safe to assume that my heater core is partially/mostly clogged and therefore causing the air bubble to last longer in the passage where the sensor is?

I know from talking to others and from other messages on this board, this is a common issue on the 4.0L engines. Something I just have to learn to live with?

Thanks.

phxmark

I believe I have fixed my issue. Tonight I pulled off both heater core hoses and flushed out the heater core. I tried pushing water through it forward first and just a trickle was flowing through it. I then ran water through backwards and the water came out like mud, along with a whole bunch of debris. I went back and forth several times until the water ran clear and flowed good.