radiator pressure when cold - ClassicOldsmobile.com

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radiator pressure when cold

Old May 22nd, 2015, 04:41 PM
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radiator pressure when cold

Can't figure this one out. The 58 burps a some for a while after a 40 mile drive when I put it in the garage. Next week when I go to check the anti freeze before I go for a ride there is a lot of pressure when I open the cap and if the level wasn't low it would have spit a lot out. This happened with the old cap. Replaced the thermostat and cap both from Fusick hoping to get the right one. The pressure should not be there after it cools down. The idiot light works and does not come on. It's not a little pressure it is a lot. Whats going on????
ED
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Old May 23rd, 2015, 06:29 AM
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Sounds like a head gasket to me. Even back in '58 cars didn't burp when they were shut down, and although a little pressure may stay in the engine if it was very well sealed, it should have virtually none when the engine is stone cold.
A carbon monoxide tester held in the filler neck when the engine is running should tell you. If it detects co it is a by product of combustion gases getting into the coolant.

Roger.
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Old May 23rd, 2015, 07:30 AM
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If it was a head gasket wouldn't it also over time give the pressure some place to bleed off? To me it just sounds like a well working, sealed sysyem.
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Old May 23rd, 2015, 09:55 AM
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A leakdown test will tell you whether there's a head gasket problem or not. I agree that a leaking head gasket would be my first assumption give the symptoms.
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Old May 23rd, 2015, 04:28 PM
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radiator pressure

Thanks for the help guy's. I will do a leak down test on the car hopefully before the end of the week. I also will do the co test as soon as I can get my hands on a co tester. Will let you know what happens. Also why doesn't it leak back into the piston???? Not enough pressure to go back????
Thanks Again ED
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Old May 23rd, 2015, 06:03 PM
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Is it positive or negative pressure in the radiator that your are experiencing?
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Old May 23rd, 2015, 06:48 PM
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Never thought of that. Unless you were paying attention you wouldn't know, it would make the same sound.
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Old May 25th, 2015, 11:54 AM
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Originally Posted by ed burke View Post
Also why doesn't it leak back into the piston???? Not enough pressure to go back????
Thanks Again ED
Combustion gases are forced into the the cooling system at very high pressure during the firing stroke if the gasket fails between the cylinder ring and a waterway, the most the return pressure can be is is what the radiator cap is rated to. Not more than 15 lb/in in most cars.

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Old May 25th, 2015, 02:59 PM
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One of mine, I check the coolant on, and it is under negative pressure (it has an overflow tank and cap) when cold. It gurgles for about a second when you crack the cap. Theoretically, if the valve is both ways, it should be -15 psig when cold, and suck coolant back in (or air, if no overflow tank) as needed to only be -15 psig. As the coolant heats, it should go up to +15 psig, then start sending fluid out the overflow line as needed to vent.

Keep your hand on the cap while doing this. Positive pressure will get your hand wet with coolant, negative won't.
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