Excessive coolant pressure?

SHOJOE

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Dec 11, 2008
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I am not sure exactly what is wrong. The coolant is excessivly over pressured to the point where it doesnt stop overflowing out the radiator. Did I blow a headgasket?
 
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ShortThrow50

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Oct 22, 2006
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you dont need to have oil in the coolant or vice versa to have a bad head gasket. I had the same issue as you about 2 years back except, my coolant was flowing out of the coolant overflow. i chnged out the head gaskets and problem was solved. so maybe its just that you need a new radiator cap. you did say that it was coming out of your radiator right? or is it flowing out of your resivoir. i would start there.
 

SHOJOE

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Dec 11, 2008
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That makes good sense. Let me try the cap first. If its not the cap it should be either the intake gaskets or the head gaskets I suspect? This problem is starting to tick me off.
 

ShortThrow50

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That makes good sense. Let me try the cap first. If its not the cap it should be either the intake gaskets or the head gaskets I suspect? This problem is starting to tick me off.
yeah just start with the simpliist things first
 

mob

the guy who hits on his mom
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3 possble causes, all are real cheap so just do them all at the same time. First change t-stat, change the cap, and put the front of the car on jack stands as high as you can and run the car without a radiator cap on untill all the air bubbles are released. I can guarantee you its your t-stat though.

Well first let me ask, is it overflowing out of the overflow bottle, or the radiator itself?
 

ShortThrow50

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Oct 22, 2006
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3 possble causes, all are real cheap so just do them all at the same time. First change t-stat, change the cap, and put the front of the car on jack stands as high as you can and run the car without a radiator cap on untill all the air bubbles are released. I can guarantee you its your t-stat though.

Well first let me ask, is it overflowing out of the overflow bottle, or the radiator itself?

cap should be first. Its easier and just as cheap. he also never mentioned overheating which could cause overheating from a "stuck closed" t-stat.
He says its coming from his rad and not his overflow which is really weird. The overflow should be overflowing before his rad cap. I have had a mildly blown head gasket before which pressurised my coolant and caused the overflow to litterally overflow. nothing ever came out of the cap. Thats why i suspect his cap to be really fugged up
 

mob

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Well change the cap first like said since its easier. He didnt say it wasnt overheating though, usually with problems like that (especially if he is considering it being a head gasket or intake gasket) it is most likely over heating. He didnt give much info though year or anything. Little more info would help.
 

SHOJOE

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Dec 11, 2008
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Its an 85 GT carbed 306 roller with afr 165's. I will be changing the t-stat and the radiator cap.
 

mob

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Is the car overheating? And is the overflow bottle filling up? Also just get a regular superstat, the Mr. gasket once are crap now since they are made in China. The superstats are made to prevent them from sticking too. At least that's what I was told.
 

RYC CUKR

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I had the same sort of issue with my 88 a few years ago after I bought it.

It never overheated but it would boil over. Swapped the cap and that took care of the boiling over problem but then the car started to overheat due to an old clogged radiator. So fixing one problem brought another one to light. Hopefully its as simple as putting a new radiator cap on it.
 

94stangnj

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Nov 25, 2009
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Help w/ my 94' 5.0

Similar frickin' problem with my 5.0. Just replaced the t-stat and put in 3row alum rad. Has a Vortech S/C. Motor runs and idles fine. No smoke out tailpipes. No apparent coolant in oil or vice versa. Overflow isn't overflowing. Crazy pressure in new top hose. Watched the temp creep up over about a half hour drive. Popped the hood, no leaks anywhere, but the gauge was pegged.
** Pump bad? Gaskets? Doesn't run rough at all and has no apparent power loss. HELP

[email protected]
 

Maryland Stang

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Aug 21, 2002
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Similar frickin' problem with my 5.0. Just replaced the t-stat and put in 3row alum rad. Has a Vortech S/C. Motor runs and idles fine. No smoke out tailpipes. No apparent coolant in oil or vice versa. Overflow isn't overflowing. Crazy pressure in new top hose. Watched the temp creep up over about a half hour drive. Popped the hood, no leaks anywhere, but the gauge was pegged.
** Pump bad? Gaskets? Doesn't run rough at all and has no apparent power loss. HELP

[email protected]

Try a Moroso balanced t-stat. More than likely you didn't get all of the air out of the intake and it won't allow the t-stat to open. The Moroso t-stat should fix your problem.