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Leaking from radiator cap, why?

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WXman

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Discussion starter · #1 ·
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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#2 ·
WXman said:
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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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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Discussion starter · #5 ·
SJZ said:
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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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. :mad:
 
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#6 ·
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.
 
Discussion starter · #7 ·
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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Discussion starter · #8 ·
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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#9 ·
WXman said:
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.....
Click to expand...
I think I have the same problem on my ZJ. You can bend the tabs on the cap, that will help.
 
Discussion starter · #11 ·
extra gasket...that's a good idea! any more?
 
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Discussion starter · #13 ·
I can blow through the overflow tube. no clogs there.
 
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Discussion starter · #15 ·
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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#17 ·
jeep overheating

It could be that you shut it off and the fans stop so that stops the extra help of dissipating the heat. Also when your on the freeways and such, the speed of travel helps keep the vehicle much cooler by the air hitting the radiator and engine versus crawling speeds that doesn't generate nearly as much air flow. I would check all the tubes, maybe one is clogged. Also it could just be that something is going out and you happened to notice it when you were 4 wheeling. Also at higher revolutions (speeds) the water pump spins faster to circulate the water/coolant. If you use too much concentration of coolant it will get over heated. Also your thermostat could be failing. Nowadays you can choose a fail safe thermostat.
 
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