While this forum is great and I really really appreciate ALL the help I've received regarding my so many questions I've had on my recent 1999 XJ.
thank you!
I'd like to now hopefully return some help by creating this thread.


Can Everyone agree to make one big thread about the coolant system? instead of a new one every three hours?

Please FEEL FREE to help me to make a solid info source for everyone to use. Chime in with facts and not too much opinion.
I know I can't cover all the needed stuff to make a complete list, so I'm asking for your help.

It's simple, if you have trouble with the coolant system on the 4.0 XJ. Start with the basics!

#1. Make sure you have a REAL temp guage- NOT the stock POS in the guage cluster.
Digital/ electrical or mechanical will give you much better readings on the actual temps.

#2. what is the current status of your XJ? if you're going to guess, then you have no clue and need to start from the top.

#3. Start with what you know. Tell us what you actually know what has and hasn't been done.

#4. Your XJ symptoms?

#5. When in doubt do the very most that you can afford. OE parts should be your first choice, if not be sure to get ones that have a solid warranty in case they fail.

#6. Skip the over the counter fixes like stop leak and other related items.

#7. Some parts are just not worth the time or effort. Example- Autozone's radiator cap is JUNK. Spend the $ for the OE. You'll plainly see the difference. (I learned after 4 of them)

#8. Always start with the simple things first. Did you check the coolant level? Are any hoses failing? where is it leaking from? Can you post pictures of your issue?

#9. If you have a 1999.5 to 2001 you might have the dreaded "0331 Head" First, you need to verify. take the valve cover off and find the casting numbers. While the valve cover is off take the time to inspect for damage near the number 3 and number 4 cylinders.

#10. Are you loosing antifreeze/ coolant, but not sure where it's going? Have you checked the oil for contamination? Maybe send it out for confirmation. Look through the oil fill hole, do you see "TUPY" stamp on the head?( that would be good)

#11.Check the play in the water pump, I have seen them worn out but not leaking, also the fins on the water pump could be worn too. check the belt tension.

#12. Does your fan clutch spin freely? Is your electrical fan going on with your a/c? Does the electrical fan go on at 218deg?

#13. What temperature thermostat is in? 195deg is stock.

#14. No need for "burping the system"
IF it's an open system and if it's working properly it will take care of itself. just add fluid if needed

#15. How did you confirm that your thermostat is working? Proper way is to put in pot with water hotter then it's rating and see if it opens, take it out and see if it closes. There is no other way to confirm, anything else would be guessing.

#16. If you're unsure about your electrical fan working or not, unplug the sensor on the thermostat housing, it should kick on the fan and a CEL.


Here is a link (I'm not associated with it, recommended by a member here): http://api.viglink.com/api/click?for...13457398807474

My renix was driving fine a couple of days ago and then it started running hot but not overheating just running hot like 220 sometimes more. I figured it was a bad thermo so I swapped it out and but still I would start up the engine and on idle within minutes shed reach red line. Keep in mind it didnt useto overheat before I decided to pull out the thermostat. Took the thermostat out and sealed the housing without a stat to see if it wouldnt overheat running freeflow but still it got hot within minutes and I squeezed the upper rad hose and it felt like no fluid was going through. No fluid was leaking while I was doing all this. My electric fan was a no show while I was doing all this testing too. Today I took out the radiator and tomorrow im taking it to a shop to have it un clogged and pretty much refurbished if it even is clogged up (only thing I can think of) since my water pump was not leaking.Any ideas what else it might be?

check the play in the water pump, i have seen them worn out but not leaking, also the fins on the water pump could be worn too. check the belt tension.

With no water in the upper hose, that might clue you in to the water pump being bad or failing.

Should I also look into my fan clutch?

There are threads here for testing procedures on the fan clutch. I didn't even test mine, the jeep had some many miles on it, I just replaced it all. Rad, pump, clutch and belt. But that's me, you can test it to make sure it's working rather than replace. I also soaked my heater core in CLR over night and flushed it with my water hose at high pressure. (youtube video for that one, ).

can this be a sticky?

Air lock in the cooling system . Jeep and Mopar are famous for air locks in the cooling systems after service/repair . Tip: Pull the Temp sensor (CAREFULLY) fill the system with the temp sensor out/loose it will allow trapped air to escape . When you get a good flow of coolant out of the sensor port tighten the sensor up and check for normal opp temp .

Ok all my overheating problems started this last winter when I noticed Jeep wasn't heating very well... Since then I have gone through and replaced water pump, thermostat, new head gasket... Only thing not replaced is clutch fan and rad. both seem to be operating properly. My question is flushing out heater core could fix my heating/ overheating issues?

How can u tell the radiator and fan clutch are operating properly? Still overheating, right?

Technically, the heater core has nothing to do with cooling the motor so it wouldn't have anything to do with overheating the motor either.

Sorry 3 year old son keeps getting out of bed and its throwing my train of thought. I ment to say that Planning on replacing radiator next, tried to flush several times and everytime I get tons of rusty, brown mucky crap out. Clutch fan comes on on start up and on shut down it stops, just assumed it was good.

Fan clutch performance slowly/gradually deteriorates with miles/age and the factory fan clutch test is quite drawn out, just because it spins doesn't mean it's pulling air thru the rad as effectively as it should......+/-$35 buys a new one, virtually assuring top performance. The radiator is the heart of the cooling system, don't delay replacing it and stay on top of the rusty coolant. Flush/change when coolant 1st starts to change color. Check it often, motor COLD.

It appears that I need to bump this so more people will start using this thread.
Sorry for dragging it back, but one thread is better then multiple overheating threads, right?

Overheating threads won't be around much longer........3-6 months of "my heater doesn't work" threads are just around the corner. Trust me, after 2 1/2 years I can speak from experience.