New to Jeeps, been a VW guy my whole life. I picked a 99 cherokee last week with 160,000 miles. I hate for this to be my first post, but I am a bit stumped. Based off searching it seems like 200 degrees or so is normal operating temp... I am in Texas cruising on hwy and the needle is consistently one dash after 210. Both fans do come on, second fan kicks on when compressor engaged or over correct temp. Coolant is super-green, but when slowing down sometimes the needle slams into the red then says check gauges, after 30 seconds, goes back to one dash after 210.... I threw on a 160 thermostat for grins, but having the same symptoms.. Oil is 10w30 and good.

Two concerns... Normal temp when running. And surging into red.

Could i have a bad temp sensor? Or a worse problem?

Any thoughts are appreciated, I am pretty handy.

 

Previous owners are notorious for neglecting maintenance. Could be a number of things. I'd start with a new fan clutch. Green coolant may/may not mean anything. The entire XJ cooling system is less than $250 in parts.

 

If both fan are spinning, how could a fan clutch be an issue? Maybe slipping and not spinning enough?

 

Fan will still spin with a bad fan clutch, it just won't spin enough.

 

A fan clutch slowly degrades in performance the moment it is installed.......but as stated, it will always spin. Green coolant in a 1/2 plugged radiator won't cool well, even though it may look good. Again, could be a number of things.

 

Good call, i will start with that. Thx for the feedback and insight. I can see this is a good forum.

Cheers!!!

 

Interesting explanation.

I noticed that my Comanche would only heat up past the center mark if it was 95* or more ambient. New fan clutch. Good at 100* ambient now. It seemed to work to a threshold, then didn't move enough air.

 

If you're having cooling problems it would be a good idea to go ahead and service the system as a whole.

Flush the system with some cleaner until it's clean, flush radiator seperate if needed. Inspect hoses, replace as needed. New water pump, thermostat, fan clutch and radiator cap.

Then you should be running tip top.

 

FWIW, the fan clutch and rad cap r about the only cooling system components that can be removed/replaced without draining/refilling the cooling system. So, if time/money permit, replace all the other components at once that do require draining the system.

It's amazing how easy it is to replace the pump, stat, belt and fan clutch when the rad is out. Just remember to lay the fan shroud over the fan before re-installing the (new) rad.

 

This ^ Just because the coolant is green doesn't mean your radiator isn't good and clogged.

 

If you are replacing the water pump, get one with metal fins. The plastic one don't hold up.

 

Where is the sensor located for the electric fan, and at what temp should it engage?

 

Need to know the year of your Jeep to answer that question accurately.