Radiator Cap Question

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MCATDT

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The coolant is boiling in the overflow on my 02 Sahara. I replaced the cap with a Stant 01234 but its still happening. I pressure tested the system and cap. Both are holding pressure. The cap does not feel like its on tightly (little to no downward pressure needed to close it) I know the previous owner replaced the radiator and I'm wondering if I need a cap with a little longer plunger(not sure if that's what you call it) to engage the lower seal better to the radiator. Is there a version of the Stant with a 1/8 " longer plunger?
 
BUMP....No thoughts on this or maybe an idea of another thing to check. Just kind of stuck on where else to look since the system is holding pressure.
 
What pressure is stamped on the rad cap?

You may have the 0331 head crack. Remove the oil cap and look straight down and see if there is coolant/sludge in there. If you see TUPY, the head has been replaced with one less prone to crack.
 
JKP said:
What pressure is stamped on the rad cap?

You may have the 0331 head crack. Remove the oil cap and look straight down and see if there is coolant/sludge in there. If you see TUPY, the head has been replaced with one less prone to crack.
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Looks pretty good in there for a 20 year old Jeep. I don't see any sludge
 

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Can't really tell from the pic, but as long as you don't see any green on the head, it's probably not cracked there.

I assume the temp gauge is in the 210 range?

The other possibility is combustion gases are getting into the cooling system. There is a test kit that will detect the gases in the coolant.
 
JKP said:
Can't really tell from the pic, but as long as you don't see any green on the head, it's probably not cracked there.

I assume the temp gauge is in the 210 range?

The other possibility is combustion gases are getting into the cooling system. There is a test kit that will detect the gases in the coolant.
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Yes temp gauge is straight up at 210.
 
KennethS said:
Well that defies the laws of physics.

Maybe I am not understanding what you mean? The radiator cap sets the pressure in the cooling system.
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The kit I have tests cap and cooling system separately. I set the pressure on the cooling system to 20 psi and it held. I tested the cap and it released pressure at 18 psi like it should and held.
 
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Did the exhaust gas leak test and it came back good. Still thinking the radiator cap is not sealing and I am going to order another one and see.
 
MCATDT said:
The kit I have tests cap and cooling system separately. I set the pressure on the cooling system to 20 psi and it held. I tested the cap and it released pressure at 18 psi like it should and held.
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Thanks for the information. Seems as if you may be correct that the cap just isn't making a good seal - there's not much else it could be.
The radiator neck where the cap goes may not be made correctly. Maybe measure the depth of the filler neck and compare that to the length of the "stopper" on the cap?
 
KennethS said:
Thanks for the information. Seems as if you may be correct that the cap just isn't making a good seal - there's not much else it could be.
The radiator neck where the cap goes may not be made correctly. Maybe measure the depth of the filler neck and compare that to the length of the "stopper" on the cap?
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The filler next is a bit deeper than the .75 spec that's why my initial question was, is there a stant cap that can hold 18 psi with a stopper an 1/8" longer than the 10234. I can't find a cross reference document on line and hoping someone here could help.
 
I have no information about cap specs. Maybe you could get a radiator shop to swap the neck with one with the correct size? I know that’s more work and expensive than just a cap swap.
 
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