XJ coolant overflow after engine is shut off

[JMA_2001XJ]

So recently my 01 XJ, 98K, started to occasionally have coolant boil in the overflow tank and come out of the overflow tank after I would shut the Jeep off. Not every time, just randomly. The temps in NY lately have not been crazy hot. It NEVER overheats while driving or at idle and the e-fan comes on at the correct temp. This only happens after you shut the engine off. Is the e-fan supposed to continue to run to aid in cooling after the engine is shut off, like on a time/temp delay? Because mine just stops when the engine is turned off. Also if I shut the engine off and then turn the key back on to the first position the e-fan does not come on either, it only seems to work when the engine is running. There is a decal in the engine bay that clearly states that the e-fan can come on at any time when the key is in the "on" position. So I am wondering if this is a bad relay or something. Any help would be great. Thanks.

 

[XJ Doc]

Couple ideas to try that work well on mine (just purchased, not responsible for the build).

Replace your thermostat with a 180 degree thermostat.

We’ve installed a secondary electric fan and switch, so for those slow crawling trips, I can circulate air through the radiator.

I’m on 33’s and just drove from CA to CO through 114 degree Las Vegas and the hottest I got was right at 230

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[JMA_2001XJ]

Couple ideas to try that work well on mine (just purchased, not responsible for the build).

Replace your thermostat with a 180 degree thermostat.

We’ve installed a secondary electric fan and switch, so for those slow crawling trips, I can circulate air through the radiator.

I’m on 33’s and just drove from CA to CO through 114 degree Las Vegas and the hottest I got was right at 230

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Thanks for the response. The thermostat was recently replaced (with OEM). As far a the fan. The overflow only happens after the car is shut off. During regular operation there is no issue. What I need to know is if the e-fan is supposed to stay on after the engine has been shut off, like on a delay till the temps drop.

 

[RCP Phx]

No the fan doesnt have a afterrun feature. I would start with a new cap and you might want to do a sniffer test while your there.

 

[RCP Phx]

It would also be a good time to do pressure test. Do not switch to a 180* thermostat!

 

[Unclewolverine]

180 thermostat is a bad idea, don't do it. It's an 01 guys, no matter what its probably a cracked head.

 

[JMA_2001XJ]

No the fan doesnt have a afterrun feature. I would start with a new cap and you might want to do a sniffer test while your there.

Thanks for the response. The cap was recently changed along with the thermostat (OEM). I also just changed the oil and it looked fine. So is the coolant boiling in the overflow tank after the jeep is shut off an obvious sign of a cracked head? I looked through the oil filler hole and could not see anything that looked like a crack between 3-4. Would that be the best way to tell or does the head have to come off to know for sure? If I do a compression test that would not necessarily tell if it is a crack or a blown head gasket, correct? By "sniffer test" what do you mean exactly? I can definitely smell coolant in the bay area. Thanks.

 

[Tim_MN]

Cracked ? Probably not.

Start with the cheap and easy stuff. Replace the radiator cap again with a genuine Jeep or STANT 16 lbs cap. You could have received a bad one.

ALL XJ 4.0L use a 195* thermostat per the Factory Service Manual.

If the new radiator cap does not solve the problem, I would consider a fresh mechanical fan clutch a good idea.

The stock e-fan does not run after engine shut-off.

My 2000 has 169,000+ miles and the original 0331 head is perfectly fine.

For the 2000-01 you can purchase and install an e-fan timer to run the fan for set time period after engine shutdown.

 

[Money_Pit_Incoming]

Throw a bottle of dye in the coolant to check for the cracked head if you don't see obvious coolant in your oil. I just recently had a cracked head, only symptom was coolant loss and eventually oil pressure. Had a pressure tester on the system for over 2 hours with 22lbs, did not drop (i dont recommend that much pressure while testing, but i was desperate). Never saw it in the oil, but after about 15 miles of driving it was obvious there was dye in the oil and the crack could be seen through the oil fill hole. Have you checked the coolant with a tester? Too much water can cause boil over. Has the system ever been flushed? The passages in the heads seem to like blocking up

 

[RCP Phx]

A sniffer test takes a sample of air in the radiator and looks for combustion gasses (sign of a leak).

 

[XJ Doc]

It would also be a good time to do pressure test. Do not switch to a 180* thermostat!

I’m curious to hear why would you recommend not changing? As soon as it was swapped from a 195 to a 180, problems went away.


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[RCP Phx]

The engine is designed based on a 195* t-stat. In your case you didn't fix the problem you just "masked" it!

 

[XJ Doc]

The engine is designed based on a 195* t-stat. In your case you didn't fix the problem you just "masked" it!

No, I’m my case it fixed it. But nice try.


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[Unclewolverine]

No, just like a new steering stabilizer masks whatever is actually causing a death wobble, a lower thermostat is just masking your actual overheating problem along with decreasing your oil life and fuel mileage. A clean, properly functioning cooling system will cool a stock xj in all but the MOST extreme conditions.

 

[XJ Doc]

No, just like a new steering stabilizer masks whatever is actually causing a death wobble, a lower thermostat is just masking your actual overheating problem along with decreasing your oil life and fuel mileage. A clean, properly functioning cooling system will cool a stock xj in all but the MOST extreme conditions.

You are correct. In most. Running a crawler through the Mojave is a little more extreme than most? So is this really masking when it is simply engaging earlier.

Guys, wheeling is as different as all of you are who are saying I’m wrong. A) I’m not wrong, because it works phenomenal for me. B) you all aren’t wrong because your methods work on yours. Let’s use the forum to help bring additional solutions to this guys problem, mine, or yours, may not be the best, so that’s why we need more solutions.


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[maxbraketorque]

You are correct. In most. Running a crawler through the Mojave is a little more extreme than most? So is this really masking when it is simply engaging earlier.

Guys, wheeling is as different as all of you are who are saying I’m wrong. A) I’m not wrong, because it works phenomenal for me. B) you all aren’t wrong because your methods work on yours. Let’s use the forum to help bring additional solutions to this guys problem, mine, or yours, may not be the best, so that’s why we need more solutions.

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You'll find a lot of resistance to a 180F tstat in this crowd. A 180F tstat has been working well for me, but I wonder a bit about whether its a proper solution for the OP's situation.

As I see it, the 4L motor stores a ton of heat in its cast iron block and head. My guess is that rust build-up in the coolant passageways prevents heat transfer to the coolant, so the engine can run hotter despite the coolant being at the target temperature. But when the engine is turned off, that heat finds its way to the coolant.

If a radiator cap swap doesn't fix the situation, the OP could consider running a rust remover through the cooling system.

 

[JMA_2001XJ]

Thank you all for your input.

I was able to spend some time with the Jeep yesterday, worried I might have a cracked head I did not want this to get worse. First thing I did was check the oil, it looked fine, there was no coolant in it. I looked through the oil filler cap to see if I could notice a crack in the head. I did not see any definitive evidence of one. Next was to test the pressure in the cooling system, right away that showed to be an issue. After I pumped it up the needle on the gauge would barely hold but coolant was not coming out anywhere. Tripple checked by removing the pressure test cap, refiling the coolant and tested again, same results. So I did a compression/leak down test and all six cylinders were very strong and even, so no issues there. That was a load off my mind. But I still could not tell where the pressure leak was coming from. After I put everything back together I tried the pressure test again and for some reason the pressure did not drop like it did with the prior tests, it held much better, still dropped a little but not like before. So with the system pressurized I started pulling on every coolant hose I could find and even checked inside under the dash at the heater core, nothing leaking, plus there was never any smell inside the cabin. When I got to the in/out at the heater core in the engine bay and started wiggling the hoses a little coolant started to come out and run down the firewall. The hoses still had the original spring clamps, so I opted to change those out for regular hose clamps. That definitely stopped the dribble and I am guessing the air leak because with another pressure test, it held. Let the Jeep get to temp and took it for a drive, got back shut it off and no issues. I need to drive it some more to double check but hopefully that fixed the problem. It was boiling over because there was a leak in the closed system and was causing the problem.
I will drive some more today and keep my fingers crossed that it was something simple like that. I know the head will still be an issue (most likely) at some point but it does not look like today was it.

 

[maxbraketorque]

A leak could have been the issue, but it would require a fair amount of coolant to leak out. A small amount of coolant loss would result in a very small plenum of water vapor in the head, and the local heating would be small. And lost coolant would be replenished by the coolant reservoir when the engine cools down. However a big leak that allows perhaps more than a quart of coolant to leak out in a single drive could allow this because then there would be large plenum of water vapor in the head that would get hotter when the engine is shut down. But I would think this could also cause the engine to run hot.

Anyhow definitely throughly burp the cooling system. Then go on several short drives with your cooling system getting up to normal temperature, while allowing the engine cool to ambient outdoor temperature between drives.

On a side note, later model XJ radiator caps have a non-sprung suction valve, so the cooling system is open to the reservoir until the coolant expansion rate is high enough to drive the suction to a closed position. When the engine begins to cool, the cap will allow coolant from the reservoir to be drawn into the cooling system as soon as the cooling system pressure drops below ambient air pressure. Earlier model non-Renix XJ radiator caps specify a preload on the suction valve, so the cooling system is sealed until the coolant system pressure drops a few psi below ambient air pressure. Also, the late model XJ radiator cap is 16 psi relief while the earlier non-Renix is 13 psi relief. The MotoRad T16V is for '96-'01 while MotoRad T13 is for '91-'95.

 

[Tim_MN]

Any coolant leak in the cooling system allows a drop in the system pressure. The 16 lbs (or 13 lbs) operating pressure raises the flash point of 50/50 coolant mix.

Loss of pressure from any type of system leak allows the coolant to flash to steam, which will vent out the radiator cap.

 

[JMA_2001XJ]

SO NOT FIXED . Went for a drive today (hot 90deg) and it boiled over again. I was really paying attention when I shut if off. I quick popped the hood and saw/heard like a gulping noise from the radiator past the rad cap (Motorad 16V) and dumping into the overflow tank and then boiling in the tank. It did not boil over because the hood was open and it could cool off quicker but it would have if I had left it closed. Could it be a bad rad cap??