Radiator cap pressurized - is this a head gasket?

Bammo68

TJ Enthusiast
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Western Australia
Recently replaced the whole cooling system (radiator, hoses, water pump, thermostat + housing) after a burst hose on my '99 led to an overheat. It was all OG so put all new system in and flushed. The Jeep is running perfectly, oil looks good and the (green) coolant looks nice and clean but I am worried about whether the overheat damaged the head gasket.

I bought a testing contraption (see below) and installed the rubber plug to test for combustion gasses. I had driven the jeep around the block first - literally not more than 3 or 4 minutes and I noticed a bit of pressure release when I opened the radiator cap. Radiator was already warm - more than I would have expected for a short cycle. As soon as I started the motor the coolant filled the little gadget and started coming out the top. No clue what colour it was turning since it all blew out the top and got replaced with coolant!

That's not right, is it? I know its supposed to have some pressure but it definitely feels like something is pressurizing the coolant system far beyond what is normal. No sign of anything amiss in the oil and no trace of any vapours out the back or loss of coolant.

I bought a spare MLS head gasket set from EngineTech but was kind of hoping I didn't need to install it... Is it cactus guys?



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turning
 
Radiator cap is rated to 18psi so I would assume it’ll blow that cork out real easy. Not trying to be a smart ass, but what do the instructions on the bottle say on how to use this tester?
I never read the directions but sometimes ya just gotta…..
 
Do you have an air bubble in the cooling system? If you do the bubble tends to make coolant surge and blow out the radiator fill.
Try running the jeep with the front end much higher than the rear , the air bubble may vent out easier.
Did the T-stat have a small hole in it to allow trapped air out ?
If you haven't driven the Jeep after you replaced the system it may a simple bubble that needs to be purged out.
Try this before you go any further " down the rabbit hole ".
It might be only pointy bushed , not cactus-ed ............
:unsure:
 
:geek:
The Philistines were an ancient people who lived on the south coast of Canaan from the 12th century BC until 604 BC, when their polity, after having already been subjugated for centuries by the Neo-Assyrian Empire, was finally destroyed by King Nebuchadnezzar II of the Neo-Babylonian Empire. After becoming part of his empire and its successor, the Persian Empire, they lost their distinct ethnic identity and disappeared from the historical and archaeological record by the late …
 
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:geek:
The Philistines were an ancient people who lived on the south coast of Canaan from the 12th century BC until 604 BC, when their polity, after having already been subjugated for centuries by the Neo-Assyrian Empire, was finally destroyed by King Nebuchadnezzar II of the Neo-Babylonian Empire. After becoming part of his empire and its successor, the Persian Empire, they lost their distinct ethnic identity and disappeared from the historical and archaeological record by the late …

Admit it, you went to Liberty Bible College ;) ;) ;) ;)
 
Back on topic, after you drive you Jeep, do you have pressure in the surge tank/overflow tank????

Is any coolant overflowing the surge tank??
 
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Are you sure that the burst hose that started this trouble wasn't caused by a head gasket compromise that is still a problem? I had that happen on a ranch vehicle years ago. Replaced the burst hose, and the new one did the same thing. Scratched my head, and then realized that the head gasket may be pressurizing the cooling system (it was). Have someone put a gauge on the radiator, or do it yourself. You test it when everything is cool. Any pressure at all indicates a head gasket compromise. I have the Stant cooling system tester and adapters - pricey, but high quality. I don't know what's available down unda, though...
 
If your jeep has a surge tank, that where you need to test for exhaust gasses in the coolant.

Run it to operating temp, then test it, but test in the surge tank.
 
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Before using that test gizmo you bought you are supposed to use a turkey baster and suck out 2-3 inches of coolant or however much you can get out given the height of the cooling tubes. Then run the warm engine before placing the tester and if more coolant rises up suck that out too before placing the tester.
 
OK thanks guys, some good advice there. The original problem with the radiator hose coming off was caused by Fingers McFuckup here - definitely not caused by an underlying head issue on the motor and the resulting overheat was very short - engine was shut off within 30 seconds of the hose coming off. I'm leaning towards there not being an issue with the gasket but the pressure had me questioning myself so I was just keen to check. I've had the new cooling system running without incident for a month or so, no noticeable overflow surges but it makes sense to either reduce the level in the radiator or check via the overflow. There are no air bubbles in the system, the thermostat has a bleed hole and as I said, the system is actually performing really well, I just wanted to check that lingering concern about the head.

The kit that I bought fits the radiator just fine - the fluid that came with the kit is badly contaminated though (was like that from the factory) so I can't actually test it again until a replacement arrives.
 
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Your cooling system was designed to run pressurized which raises the coolant's boiling temperature. Your radiator is protected by an 18 lb. radiator cap which vents any pressure over that 18 lbs.
 
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The original problem with the radiator hose coming off was caused by Fingers McFuckup here - definitely not caused by an underlying head issue on the motor and the resulting overheat was very short - engine was shut off within 30 seconds of the hose coming off. I'm leaning towards there not being an issue with the gasket but the pressure had me questioning myself so I was just keen to check. I've had the new cooling system running without incident for a month or so, no noticeable overflow surges but it makes sense to either reduce the level in the radiator or check via the overflow. There are no air bubbles in the system, the thermostat has a bleed hole and as I said, the system is actually performing really well, I just wanted to check that lingering concern about the head.

Sounds like you'll be fine. The above description of the situation wouldn't cause me to believe any permanent damage was done, but it certainly doesn't hurt to check.
 
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Your cooling system was designed to run pressurized which raises the coolant's boiling temperature. Your radiator is protected by an 18 lb. radiator cap which vents any pressure over that 18 lbs.

And Jerry's statement is the reason you do the exhaust test in the surge tank.
 
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Before using that test gizmo you bought you are supposed to use a turkey baster and suck out 2-3 inches of coolant or however much you can get out given the height of the cooling tubes. Then run the warm engine before placing the tester and if more coolant rises up suck that out too before placing the tester.

Yeah, you gotta reduce the coolant level first. I had the same problem with coolant going into the tester. Wasted a lot of test fluid before I got good readings and convinced myself everything was OK.
 
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