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1999 XJ Overheating at Speed

CO99XJ

NAXJA Forum User
Location
colorado
This is my first post so I'll try not to screw up. I think I've read every post on here about overheating and thermostat replacement. Here's my problem. My 99 XJ, 110,000 miles, can sit an idle forever and not run much over 210 but at speed and hard acceleration the temp gauge will jump to 240 (first orange line), sit there and then drop back to a little over 210 once I let off the gas. I just had the coolant flushed and I’m thinking it’s either a clogged radiator or a bad thermostat. If it's the radiator how hard is it to change? Any feedback would be greatly appreciated.
 
Check your lower radiator hose. It should be hard when you squeeze it. OEM hoses have a spring-like metal thing inside so that they don't collapse at high RPM. Did you have the hose replaced with a non-OEM?

If this is OK, check the thermostat next.
 
Sounds like a bad fan clutch to me. Use "fan clutch" in your search to see what's been written on the topic.
 
Had the same problem with my 96. I went through all the checks. The fan clutch, the lower hose. Even wound some tubing and put it in the lower hose to avoid a possible collapse.

It turned out to be the radiator was cloged. Replace the rad and upgrade. It is not hard to do.

Mike
 
Jldiaz, Thanks for the info....I checked the lower hose and I could feel the spring inside so it appears to be an OEM hose. It sounds like the thermostat is realatively easy to replace. Do you happen to have any instructions handy that I could use or a good reference to check? I'm intereted in buying the FSM but it's pretty pricey. Thanks again for your help.
 
MK96XJ...thanks for the help. Do you have any reference materials for the radiator change? I'm intereseted in doing the change because I know the dealer will screw me. They wanted $180 just to change the thermostat.
 
Hey, change the thermostat first even though it is probably not the problem just because it is so cheap. It is easy to change: The upper radiator hose leads to a metal housing on the top, front of the engine. The stat is under that housing. Remove the 2 13mm bolts and it will come off. Upon replacing, make sure both metal surfaces have been scraped clean of the gasket, and tighten down the bolts good, but not too tight. Also, the radiator is pretty easy, just remove all of the bolts on the long metal panel above it, and it slides up and out. By the way, make sure you aren't just simply low on coolant. With Jeep running and fully warmed up and heat on high, fill rad with water from garden hose, and fill recovery bottle to full line. Be careful about removing cap when engine is hot, though.
 
Jackhill442...thanks for the info. I'm going to take a look right now for the thermostat. Do I need to worry about the transmission cooler since mine is an automatic? Thanks again.
 
You didn't mention that you need to drain the radiator first did you?

I don't remember if you have the open or closed radiator system, but if it is the open system, replace your radiator cap while you are at it. They get old and cause a lot of problems. They are pretty cheap and well worth the expense.
 
I have the open system. Does the radiator have a pet**** on it? I looked but I couldn't find one. Also I'm going to replace the cap this week. Any suggestions on where to get the cap? Autozone? Thanks for your help old_man!
 
Sounds like a clogged radiator to me.

Fan clutch being bad would make it overheat while sitting I would think as it's not pushing enough air.

Overheating at speed is usually from a clogged radiator as the water is only passing through part of the radiator and doesn't have time to cool off.

Also if overheating under accel. you could be running lean. Check map sensor and O2 sensor and whatnot.
 
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Mine is an aftermarket GDI so it may be different, but mine is on the passenger side, end of the radiator. Not the front or back but on the end. I get to it from the wheelwell.

Like the man said, it is most likely a clogged radiator, but try the simple cheap stuff first.
 
Overheating at speed is generally not the fan clutch, the fan clutch only engages at low speed to pull more air thru when crawling or idling.
Step one, replace the thermostat, one bad overheat can destroy a new one. as well as the pressure cap. Use a dealer supplied OEM one, it comes with the correct gasket all set to install. Put the little bleed hole in it at the top or 12 O'clock position.
When refilling refill with only a 50/50 mix of coolant and DISTILLED water. Fill it with the engine off, fire it up and let the thermostat open, as it sucks coolant down add more mix and keep it filled to the top of the filler bung, it will look like green fizzy soda, thats air, object is to bleed it out. Also remove the overflow bottle before all this starts and clean it out, reinstall it and fill to between the hot and cold marks.
Once you have all the air out, or the gross amounts anyway, the overflow bottle should take care of the rest over a few days of running.
 
Thanks RichP.....looks like I'm going to be in the market for a new radiator. I know it's a lot to ask but can someone give me a step by step on replacing the radiator? I'm a little uncomfortable with how to drain the coolant. Also are there any special tools that I'll need. I have a basic set but nothing extensive. My email address is [email protected]. Thanks all!
 
CO99XJ said:
Thanks RichP.....looks like I'm going to be in the market for a new radiator. I know it's a lot to ask but can someone give me a step by step on replacing the radiator? I'm a little uncomfortable with how to drain the coolant. Also are there any special tools that I'll need. I have a basic set but nothing extensive. My email address is [email protected]. Thanks all!


To drain the radiator just unhook the lower radiator hose. Have a bucket underneath to catch the coolant.


I'd bet your radiator is the problem. If your thermostat was bad it would overheat at any speed and not cool back down. 110,000 miles is about the service like of a radiator, especially if it hasn't been flushed ever 40,000 miles or so. I would go ahead and replace it though while you have the coolant drained. Good luck.
 
To replace the rad:
1. drain old coolant
2. remove bracket that attaches front fascia (grille surround) to top core support (where hood latch striker is located) There are about 6 nuts and 6 bolts that hold this angle bracket in place
3. undo the 3 bolts on each end that attach the core support bracket to the fender extensions
4. undo the nuts that hold the AC condenser to the core support bracket, if so equipped
5. remove the core support bracket, exposing the top of the rad
6. remove the auxiliary electric cooling fan
7. disconnect the two automatic trans. cooling lines at the radiator
8. disconnect the upper and lower rad hoses at the radiator
9. lift the radiator up out of the vehicle.
10. reassemble in reverse order
11. fill system with plain fresh water only, and run to check for leaks and flush remaining cruddy water from engine block.
12. drain cooling system again to remove the plain water, and refill with 50/50 mix of antifreeze and distilled water.
 
Thanks all...I've been reading more threads and I'm a little nervous about the transmission cooler lines. Are there any tips and tricks I should know about? Do I even need to worry about the transmission cooler? Thanks again, Ryan.
 
When you remove and reconnect the tranny cooler lines, watch out for the o-rings inside. I found out they are very easy to cut.
 
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