overheating...

Hello! Long time lurker, first time poster.

My 2001 XJ 4.0 keeps overheating and I've exhausted my understanding of the cooling system to understand what the heck is going on.

Basically it runs slightly hot, all the time. Like, 3-4 millimeters past the halfway (210) mark. Not really sure what that temp would be, 230 maybe?

It will stay at that temp on the highway, but often, when idling, the temp will shoot up into the red. If i start moving again quickly (within 5 seconds or so), the temp goes back down immediately and will stay that way for awhile.

In troubleshooting this, I found a lot of spray around the new radiator cap when it did overheat, so I replaced it with the stant model per the forum posts. I thought this fixed it, as I was able to idle it after warming up for well over 15 minutes, and drove it around with plenty of stops with no issues. That was 2 weeks ago.

Last night after about an hour of highway driving, I pulled over to get more gas, and while idling (no more than 7 seconds) the temp shot up again (like whaaat?).

I found that as long as I'm moving, the temp will stay fine (if a bit hotter than normal). Here is the full sordid history of my cooling if it helps.

About 2 years ago I'm heading out on a long (7 hour) trip. XJ is packed up and we stop to get tacos. Overheats in line for the first time. In my infinite wisdom I quickly stop at the auto store and top off the radiator fluid in hopes that is the problem, except, I put in concentrated (non-diluted) fluid.. OOPS

6 months later, the radiator springs a leak, spraying fluid out the front of it. I replace the radiator, thermostat, flush the system, and all is well.

Fast forward to present time. Fluid is now sorta brownish (but still mostly green). Thinking it could be the fan clutches, I replaced those. Not much better. Thinking my thermostat might be stuck, I removed it. Still the same problem.

What do I do next? Since the fill portion of my radiator is sticking out the side I can't see if water is flowing or not, but considering I can drive 3 hours straight (without stopping) I figure the water pump must be working.

The next thing I plan to do is flush and replace all the hoses, which doesn't make any sense, but I'd rather not change the water pump "just because."

Thanks!:thumbup:

Why do you assume that the water pump is working at full capacity ?

Like brakes, tires, or mufflers, cooling system parts are replaced when they fail, when they no longer perform efficiently, or when have reached the end of their service life.

Consider that you may have cracked the 0331 head by overheating. Test and inspect for damage, and/or mixing of the coolant and oil.


The cooling system is a group of related parts that depend on proper function from each of its component parts to keep the engine cool. Service the cooling system and replace any under-performing or suspected weak parts. Any component part of the cooling system that is not fully doing its job will stress the others and your cooling system will overheat. The most important maintenance item is to flush and refill the coolant periodically. Anti-freeze has a number of additives that are designed to prevent corrosion in the cooling system, but they have a limited life span. The corrosion causes scale that eventually builds up and begins to clog the thin flat tubes in the radiator and heater core, causing the engine to eventually overheat. Coolant should be replaced every 36,000 miles or every three years.



-Use a flushing/cleaning solution and then drain and fill the radiator with a fresh 50/50 coolant and water mix. With a neglected cooling system you may have to flush several times.
-Inspect the radiator for mud/bugs/grass clogging the outside and mineral deposits clogging the inside. Clean or replace as needed.
-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

If you have covered all the points listed above and still have overheating issues, inspect the head for cracks and head gasket for leaks. Exhaust gasses entering the coolant can raise the temperature of the coolant or cause steam pockets in the coolant that will temporarily block the flow of coolant

Read more about cooling systems here –

www.offroaders.com/tech/engine-overheating.htm

www.familycar.com/classroom/coolingsystem.htm

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Hey Tim, Thanks for the lengthy response! This gives me plenty to look at over the weekend.

To your points:

Flush and hose replacement is next

Radiator isn't bug infested, cooling fins are fine

Thermostat has been removed

The radiator cap is brand new, stant model as suggested by this forum

Fan clutches have been replaced

Electric fan kicks on once the engine is at temp

Have not replaced coolant temp sensor, but I'm pretty sure its reading correctly as when it shows overheated I can smell it, the hoses are HOT and coolant is spilling into the overflow, sometimes boiling.

I checked the oil last night and it didn't look milky. I will check again today. Good point about the head, any other checks to do other than looking at oil?

If the head is fine then I'm looking at water pump, hoses, flush, and fill.

space_monkey said:

Thinking my thermostat might be stuck, I removed it. Thanks!:thumbup:

Click to expand...

Put a thermostat back it, taking it out will not fix any problem except a stuck closed unit. It can actually make the truck run hotter by not restricting the fluid enough.

Tim_MN said:

-Replace the thermostat with a STANT or Robertshaw 195* thermostat. Cheap thermostats are cheap for a reason.
-Replace the radiator cap if your Jeep has one. An old worn out cap will allow boil overs and/or allow the coolant flash over into to steam. You will see the coolant temps suddenly jump from 210* to the Red Zone and back to 210* if your radiator cap is weak.
-Inspect/test or replace the mechanical fan clutch. A worn fan clutch will allow temperature creep at stoplights, in heavy traffic, and on the 4x4 trails. A fan clutch that “looks” OK is not the same as working OK.
-Inspect the electric cooling fan and the fan relay. Apply 12 volts and make sure the fan runs. Exchange the cooling fan relay with one of the others similar relays. Confirm that the e-fan starts when engine temps reach 215-218*. Repair or replace the fan or relay as needed.
-Inspect/test or replace the coolant temperature sensor that activates the e-fan.
-Replace the water pump. The pumping fins can deteriorate over time and the pump will not flow enough coolant to keep the temps under control.
-Inspect/replace the radiator hoses. Make sure the coiled wire is installed in the lower hose.

Click to expand...

Amen, great stuff

space_monkey said:

Thermostat has been removed

Click to expand...

put a quality thermostat back in. I recommend the stant superstats. they are supposed to always fail open by design. Running the system without a thermo does you no good.

Also, driving at highway speeds should be enough to keep the radiator cool. That's why it cools down when you're driving.

Yeah, I took the thermostat out for troubleshooting, to make sure it wasn't stuck. I'll put a new (stant) one back in once I figure out the problem.

Also, it seems that even less than highway speed is enough to cool it back down and keep it cool. Sorta happens like this.

Stop at intersection
Wait 10-15 seconds
Temp jumps into red
Start moving again, maybe 20-35 mph
After 3-6 seconds, temp goes back down.

As long as the jeep stays moving, its good, if a little warmer than usual.

I would guess one of two things, bad fan clutch or a bad waterpump

The waterpump may not be pumping enough at idle, if it is worn out and falling apart it can happen. Moving the combo of airflw and higher rpms will move enough water and cool it. Sitting still not so much.

The fan clutch you said was new but I would test it a little.

And you need a working thermo in the truck to verify that everything else is working correctly. I would put that back in first.

I would guess one of two things, bad fan clutch or a bad waterpump

The waterpump may not be pumping enough at idle, if it is worn out and falling apart it can happen. Moving the combo of airflw and higher rpms will move enough water and cool it. Sitting still not so much.

The fan clutch you said was new but I would test it a little.

And you need a working thermo in the truck to verify that everything else is working correctly. I would put that back in first.

I agree the fan clutches cant be ruled out either. Funny thing is when i removed the old ones they appeared to be stuck, like, harder to move than the new fan clutches, which move easier, so the old ones probably moved more air Would it make sense to remove the clutches then do the mod where the fan is always fully engaged?

I'm beginning to suspect the water pump as well after all these suggestion, and it seems like a cheap enough part so I will try that this weekend along with the hoses.

Initially removing the thermostat had no effect. It was new rad cap that made a difference, but now I'm right back where I started. Might as well get the stant one and put that in when doing the pump.

Any particular brand suggestions for the pump? I was just gonna call Advance Auto and see what they had (been burned by auto zone too many times).

space_monkey said:

Any particular brand suggestions for the pump? I was just gonna call Advance Auto and see what they had (been burned by auto zone too many times).

Click to expand...

Buy a new water pump, not a re-built.

Advance/IdiotZone/PepBoys sell the same crap. I prefer NAPA for my parts.

Whatever "new with lifetime warrenty" pump that advace sells. When I worked there I saw too many of the reman pumps come back. Plus the price difference is not that much.

Roughly $30 for a new pump with lifetime warranty from Advance.

As mentioned though, all the parts houses sell basically the same things. I had a brand new Napa WP fail in mine after only 6 months.

What do you guys think of the Hesco water pump?http://www.hesco.us/shop.asp?action=details&inventoryID=45086&catId=7967

personally I think it is a waste. Very few people actually have a need for a high performance water pump.

I am running a 4.7stroker, with a stock WP, Stock 198deg thermo and housing, stock hoses, a 3 core radiator, and a 18lb cap. I run 60/40 water to antifreeze, with a little water wetter to combat electrolysis. I am currently running no fans at all. At speed in the eastern NC heat I have been running 195-200. As long as there is any airflow I am fine. I will be putting fans on, but since this is my toy now, I can be choosier at the JY when looking for some electrics.

Just a reminder, the thermostat need to have a bleed hole in it. I use an 0.125" bit to drill the ones I use. Be sure to place it with the hole at the 12 o'clock position. This hole allows the system to burp out quicker. Or, just get one from the dealer as those already have the bleeder installed with a check valve.

the last stant I bought had a bleeder check valve on it.

I just took the water pump out and sure enough, the fins are busted. Almost totally corroded. Looks like that is the problem but I will go ahead replaces all the hoses and serpentine belt since I already have it apart.

Yep, its all good after changing the water pump. Thanks for the suggestions everyone, especially Tim_MN, huge help!

So the water pump fixed it, nice to here the problem was resolved.

Just keep an eye on the head between cylinders #3 and #4 , you can pull the oil fill cap and look straight down to check for a crack. If you have a 2001 xj built towards the end of the year your head should be the new casting. Just something to keep an eye on.