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Unread 09-29-2009, 08:01 AM   #1
WXman
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Leaking from radiator cap, why?

Had a coolant leak coming from the radiator cap. Bought a new cap, still leaks. When it's hot, and I shut the Jeep off, it leaks out from the cap and sometimes does it pretty bad. What's going on?

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Unread 09-29-2009, 01:33 PM   #2
SJZ
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Quote:
Originally Posted by WXman View Post
Had a coolant leak coming from the radiator cap. Bought a new cap, still leaks. When it's hot, and I shut the Jeep off, it leaks out from the cap and sometimes does it pretty bad. What's going on?
As the coolant heats up, pressure in the cooling system increases. When the pressure is greater than the rated pressure marked on the radiator cap, the spring in the cap will compress, and coolant will flow past the cap & into the plastic overflow tank. As the engine cools down, coolant is drawn back from the tank into the radiator.
Check for a leaking joint where the small nipple for the coolant overflow hose goes into the radiator neck, a leaking overflow hose, or dirt where the rubber radiator cap gasket seats onto the radiator neck. Also make sure the overflow hose is not cracked or split.
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Unread 09-29-2009, 04:36 PM   #3
driabyor
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head gasket too maybe
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Unread 09-29-2009, 07:27 PM   #4
HighLonesome
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get an OEM cap too
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Unread 09-30-2009, 05:33 AM   #5
WXman
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Quote:
Originally Posted by SJZ View Post
As the coolant heats up, pressure in the cooling system increases. When the pressure is greater than the rated pressure marked on the radiator cap, the spring in the cap will compress, and coolant will flow past the cap & into the plastic overflow tank. As the engine cools down, coolant is drawn back from the tank into the radiator.
Check for a leaking joint where the small nipple for the coolant overflow hose goes into the radiator neck, a leaking overflow hose, or dirt where the rubber radiator cap gasket seats onto the radiator neck. Also make sure the overflow hose is not cracked or split.

It's not coming from the overflow tube, it's actually running out from the cap itself. This is a new (but non-OEM) radiator, and I have two radiator caps now that both let coolant come out. This radiator was run all Summer long with no trouble...now all the sudden the cap is letting coolant come out.

Could I have air in the system somewhere or what? This is annoying me because it's leaking bad enough to drain the reservoir every other day or so.
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Unread 09-30-2009, 05:58 AM   #6
cmonson
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look at the gasket on the cap. Make sure if is in good condition.

a leak is not caused by air in the system.

maybe the mating surface on the non-mopar rad is not perfectly flat. Inspect it and see. Maybe use a file and make sure your cap will seal properly.
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Unread 09-30-2009, 07:31 AM   #7
WXman
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OK I'll check it. I think you are right...it's probably the non-OEM radiator "neck" that's the problem.
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Unread 10-02-2009, 11:07 AM   #8
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OK so the problem is that the detent made onto the neck of the radiator isn't thick enough to pull the cap down hard enough to seal everything off as you tighten the cap. If you press down on the cap with your hand, the leak stops. If you turn the cap so that the tabs are directly on the first detent, it'll hold the cap tight enough to stop the leak also. But if you go ahead and fully turn the cap to the position where it stops, the leak returns.

I guess I need to find a way to make the resting detent on the radiator neck thicker, so that when the cap is turned to that position the tabs will hold the cap down tighter. Any ideas on how to do this? I am brainstorming too.....
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'92 YJ - heavily modded
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'05 KJ CRD Limited - 370 lb./ft. from a 4-cylinder and trail ready. Pure awesomeness.
'11 Mango Tango JKU Sport - Mods
'12 Dozer JKU Sport S - 6-speed - ACE rock rails - Max Tow package - Daystar spacers - 33x12.50 Duratracs
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Unread 10-02-2009, 01:10 PM   #9
HighLonesome
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Quote:
Originally Posted by WXman View Post
OK so the problem is that the detent made onto the neck of the radiator isn't thick enough to pull the cap down hard enough to seal everything off as you tighten the cap. If you press down on the cap with your hand, the leak stops. If you turn the cap so that the tabs are directly on the first detent, it'll hold the cap tight enough to stop the leak also. But if you go ahead and fully turn the cap to the position where it stops, the leak returns.

I guess I need to find a way to make the resting detent on the radiator neck thicker, so that when the cap is turned to that position the tabs will hold the cap down tighter. Any ideas on how to do this? I am brainstorming too.....
I think I have the same problem on my ZJ. You can bend the tabs on the cap, that will help.
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Unread 10-02-2009, 03:59 PM   #10
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bend the tabs. also, add another rubber gasket. That shoulf fix it.
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Unread 10-02-2009, 05:46 PM   #11
WXman
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extra gasket...that's a good idea! any more?
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'05 KJ CRD Limited - 370 lb./ft. from a 4-cylinder and trail ready. Pure awesomeness.
'11 Mango Tango JKU Sport - Mods
'12 Dozer JKU Sport S - 6-speed - ACE rock rails - Max Tow package - Daystar spacers - 33x12.50 Duratracs
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Unread 10-02-2009, 07:38 PM   #12
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Your coolant overflow system may be clogged.
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Unread 10-03-2009, 05:50 AM   #13
WXman
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I can blow through the overflow tube. no clogs there.
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'05 KJ CRD Limited - 370 lb./ft. from a 4-cylinder and trail ready. Pure awesomeness.
'11 Mango Tango JKU Sport - Mods
'12 Dozer JKU Sport S - 6-speed - ACE rock rails - Max Tow package - Daystar spacers - 33x12.50 Duratracs
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Unread 10-03-2009, 07:45 AM   #14
cmonson
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it is your cap. double gasket it and bend the tabs a little.
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Unread 10-03-2009, 07:52 PM   #15
WXman
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OK I bent the tabs some and it seems to have maybe stopped the leak. Ran it until hot in park and no leaks visible...will find out for sure when I drive it next time.
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'92 YJ - heavily modded
'96 ZJ - heavily modded
'05 KJ CRD Limited - 370 lb./ft. from a 4-cylinder and trail ready. Pure awesomeness.
'11 Mango Tango JKU Sport - Mods
'12 Dozer JKU Sport S - 6-speed - ACE rock rails - Max Tow package - Daystar spacers - 33x12.50 Duratracs
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