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Overflow Reservoir Dumping Coolant After Shutoff

AjHenzy

NAXJA Forum User
Location
Davenport, IA
Hello, I have a 2000 Jeep XJ with the 4.0 inline 6 cylinder engine. After driving 15-20 minutes around town, and shutting off the vehicle, the coolant reservoir begins to fill and overflow to which it dumps on the ground. There are times when I drive longer time/distance and this doesn’t happen (30-60 minutes). I have replaced the thermostat (195deg), radiator, and radiator cap (16psi). I fill 50/50 coolant just right above the “add” line in the reservoir. All the hoses seem to be in good condition. I’ve also flushed the cooling system twice. And burped the system (Yes, on an incline). I have no other symptoms that would point to a blown head gasket or cracked head. Any input would be greatly appreciated. She only has (66,000) miles on her, and is pretty much as stock as you can get. Thanks


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Have the cap pressure tested. This typically means it is not holding pressure when it fills the overflow like that.


Thanks for the quick reply. I will surely do this tomorrow if not, buy a new cap all together. I ran a 18 psi cap a while ago, and I noticed it didn’t spill into the overflow tank anymore. But it was running my engine temp hotter than normal for some reason. So I switched back to the old 16 psi cap, lo and behold started dumping again


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Check or replace the radiator cap, and the thermostat. I have had thermostats that either were poorly made in China, or were mixed-up by some Idiot at the auto parts store.

Test for head gasket issues. An 18 psi radiator cap shouldn't make the engine run hotter.

Do a bit of research about Jeep 0331 heads cracking, but keep in mind that the number of actual proven cracked heads are far fewer the number threads about the cracks.
 
Check or replace the radiator cap, and the thermostat. I have had thermostats that either were poorly made in China, or were mixed-up by some Idiot at the auto parts store.

Test for head gasket issues. An 18 psi radiator cap shouldn't make the engine run hotter.

Do a bit of research about Jeep 0331 heads cracking, but keep in mind that the number of actual proven cracked heads are far fewer the number threads about the cracks.


Copy that, thank you. I will keep that in mind.


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A 50/50 mix at 16-psi will boil at 273*F. What kind of temps are you running? Boil over after shutdown usually means a loss of pressure and/or a hot spot in the head that boils the coolant once it stops moving and carrying away heat.
 
A 50/50 mix at 16-psi will boil at 273*F. What kind of temps are you running? Boil over after shutdown usually means a loss of pressure and/or a hot spot in the head that boils the coolant once it stops moving and carrying away heat.


I run around 210° degrees fahrenheit typically the needle is slightly under or slightly over (210°) when driving around town/ idled/ or on the highway.

Side note: I’ve changed my radiator cap and the issue appears to have subsided. I will still monitor closely though. Very hot ambient temperatures today as well.


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