Over heat, crappy radiator

Thank you for the correction, Techno1154. On my guage, if I'm not driving, I -usually- hear it kick in "a bit" after 200. So "after 210" makes sense.

Late-spring this year, I had some over-heating (pulling a trailer, and/or long, lower-gear, high-RPM runs on hills.) Then I noticed my Aux-fan wasn't running ('89 XJ, RENIX.) I found corroded terminals on the Relay (left quarter-panel, mounted to the rear of the ceramic resistor.) Cleaned up the 'spades' and as much as I could of the socket... and the Aux-fan has worked fine since then.

My point in asking the question of "Magus" is... if the Aux ain't running, there might be a simple (and less expensive) solution.

I would do a pressure test of the cooling system. Check condition of the rad cap as well. Also, use an IR gun in different locations to confirm temp and potential issues.
Unless there was steam and boil over when the "temp gauge was at the next mark", I would definitely confirm operating temp.
Stock gauges are know to be inaccurate. The gauge in my XJ shows close to 10 deg. over What actual temp is. That "third tick" is approx 230 if gauge is correct. Not terrible under specific conditions, but high if it is correct.
Incorrect coolant/water ratio can also be cluprit if in extreme, hot or cold conditions.
I always use a bottle of "Water Wetter" when I do a flush/change.

Definitely check cooling fan operation. And, if running AC in some of these conditions can affect this problem as well.

Podunk said:

Thank you for the correction, Techno1154. On my guage, if I'm not driving, I -usually- hear it kick in "a bit" after 200. So "after 210" makes sense.

Late-spring this year, I had some over-heating (pulling a trailer, and/or long, lower-gear, high-RPM runs on hills.) Then I noticed my Aux-fan wasn't running ('89 XJ, RENIX.) I found corroded terminals on the Relay (left quarter-panel, mounted to the rear of the ceramic resistor.) Cleaned up the 'spades' and as much as I could of the socket... and the Aux-fan has worked fine since then.

My point in asking the question of "Magus" is... if the Aux ain't running, there might be a simple (and less expensive) solution.

Click to expand...

I have been diagnosing overheating Cherokees for 15+ years on here. First off, before dropping major cash on a radiator, lets make sure it is the problem.

Are you running a shroud around the fan? If not, you REALLY need to. I run a 4.7L stroker here at high altitude and don't have overheating problems.

Do you have A/C? If so, is the condenser clear of debris and the fins aren't all bent up? The air has to go through the condenser before it can get to the radiator. No flow means overheating.

Do a search on checking out the fan clutch. It is old and crappy, you won't get any air flow.

If the radiator cap is more than 2 years old, replace it. Make sure you are using a 16lb cap. A cap that won't hold pressure will cause no end of problems. It is a cheap item and should be changed regularly.

You should have an AUX fan on the driver's side. Make sure it kicks on with the A/C and when it gets hot.

Never trust you factory temp gauge. Use an IR temp gauge and verify the actual temps.

Make sure the lower radiator hose is not collapsing when it gets hot. Original OEM had a spring in it to combat this problem. Aftermarket hoses are hard to find with the spring.

If you open the radiator cap, what color is the coolant? If it is nice and clear, you are probably fine.

If you find nothing to this point, I would run a radiator flush. You have nothing to lose.

Put a vacuum gauge on the intake and monitor the vacuum. A vacuum leak can cause the motor to run lean/hot. It can also cut down your power and ultimately destroy your engine. If that is it, it is most likely a cheap fix.

Once you go through all these steps and don't find anything suspect the radiator. If you have a radiator shop local, you might want to have them rod the radiator and all might be fine.

Remember that the 4.0L is a long skinny block and has a terrible problem getting trapped air out of the system. On a Renix it is easy, you can loosen the temp sensor at the rear of the head. On HO's you need to park it up hill and fill through the upper radiator hose.

Good Luck.