overpressurized coolant system
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New User
Joined: May 2009
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From: stockton,ca
overpressurized coolant system
I have a 86' f250 with 6.9 diesel.I recently replaced entire coolant system including radiator,waterpump and ford thermostat.Now it is repeately blowing upper hose .I think also it is running warm for having new coolant system.It has over 30 lbs of pressure in coolant system.I fear it is a head gasket or worse a cracked head.ALso did a compeesion check all were a 400psi but cylinder 6 was at 375psi.Any suggestions before i rebuild another 6.9?
FTE Leadership Emeritus
Joined: May 2001
Posts: 13,653
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From: Cabot, Arkansas
Welcome to FTE!! I had a similar issue a little over a month ago. Blew coolant all down the side of the truck every time I loaded the engine. Two new head gaskets and a set of studs fixed me right up.
Lead Driver
Joined: Nov 2003
Posts: 6,900
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From: Campbell River, B.C.
I think cookie is right, but why do you say "another" 6.9?
Is this a fresh engine?
Might be a good idea to have the heads pressure tested if you decide to pull them.
I also have to ask, what do you have for a rad cap?
Is this a fresh engine?
Might be a good idea to have the heads pressure tested if you decide to pull them.
I also have to ask, what do you have for a rad cap?
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New User
Joined: May 2009
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From: stockton,ca
Thanks guys for the help.I meant other 6.9 because I have to keep my truck running to move around in drive way. The radiator cap is a lever vent that is 13 lbs.The mileage is unknown but it service was terrible. I got the truck $ 750 and you get what you buy. .Also i have found a 1000,000 mile 6.9 with banks kit for $750 complete.I'll throw a stud kit and gasket kit in it? What do you think guys?Also has anybody put larger valves in 6.9 cylinder heads and port work?
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Joined: Apr 2007
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From: Conway, AR
Before condemning the engine, get a combustion gas leak detector kit. About $50 from NAPA , a little moer for a better 2 chamber one from snap on.
You pour a blue dye into a plastic chamber and hold it over the radiator neck ( make sure to draw coolant down where it wont suck up into the thing or it will contaminate the test ) and you pump the air off from the inside of the cooling system through the liquid witha bulb. If there is combustion gas present in the cooling system, the fluid will change to a green/yellow. Then you will know for sure if you actually have a problem.
You pour a blue dye into a plastic chamber and hold it over the radiator neck ( make sure to draw coolant down where it wont suck up into the thing or it will contaminate the test ) and you pump the air off from the inside of the cooling system through the liquid witha bulb. If there is combustion gas present in the cooling system, the fluid will change to a green/yellow. Then you will know for sure if you actually have a problem.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
6.9smoker,
Welcome to FTE and the IDI diesel forum.
30 PSI in the cooling system is way to much, be careful or you will damage your new radiator and heater core.
Best thing to do here if you can.
Get an adapter that lets you put shop air into the cylinder through the glow plug hole.
Remove the rocker covers and rocker arms.
Fill the radiator to the neck, now remove a glow plug and put shop air into the cylinder, CAUTION THE ENGINE WILL ROTATE TILL THAT PISTON IS AT BDC.
Not a problem, it won't rotate far, but enough you can get something under a belt like a finger or cord which could be bad.
Look for the coolant to rise or bubbles in the radiator.
If none are seen and the coolant level does not rise, go to the next cylinder.
This will test the head gasket, head and block for cracks.
When the coolant level raises or you see bubbles, you have found the leak.
When you find the cylinder that is leaking, you know where to look for the problem when you tear it down.
Welcome to FTE and the IDI diesel forum.
30 PSI in the cooling system is way to much, be careful or you will damage your new radiator and heater core.
Best thing to do here if you can.
Get an adapter that lets you put shop air into the cylinder through the glow plug hole.
Remove the rocker covers and rocker arms.
Fill the radiator to the neck, now remove a glow plug and put shop air into the cylinder, CAUTION THE ENGINE WILL ROTATE TILL THAT PISTON IS AT BDC.
Not a problem, it won't rotate far, but enough you can get something under a belt like a finger or cord which could be bad.
Look for the coolant to rise or bubbles in the radiator.
If none are seen and the coolant level does not rise, go to the next cylinder.
This will test the head gasket, head and block for cracks.
When the coolant level raises or you see bubbles, you have found the leak.
When you find the cylinder that is leaking, you know where to look for the problem when you tear it down.
Senior User
Joined: Apr 2007
Posts: 315
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From: Conway, AR
Problem with the bubble test is many times the leak is so small that bubbles will not appear ( especially in diesels ). That;s where a combustion gas leak detector kit shines. It will detect the most minute presence of combustion gasses in the cooling system. I've had many that showed no bubbles, even when put under load that failed the combustion gas leak test.
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
If the radiator cap is not able to vent pressure fast enough to prevent hoses from blowing, the leak is no small leak.
When I had a reman cracked block, 30 PSI in the cooling system in 15 seconds of cranking.
I never blew a hose, but there was so much compression gasses venting through the cap, it blew everything out of the coolant reservoir.
How big was the crack?
The method above lead me right to the problem.
When I had a reman cracked block, 30 PSI in the cooling system in 15 seconds of cranking.
I never blew a hose, but there was so much compression gasses venting through the cap, it blew everything out of the coolant reservoir.
How big was the crack?
The method above lead me right to the problem.
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