excessive pressure in the cooling system

Diesel Dave

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This started suddenly last week. The cooling system has been building high pressure in the radiator and burping coolant through the overflow tank. I thought the cap might be bad so I changed that last night. This morning on the way to work it threw-up again within a mile from the house. It seems to be doing it when the thermostat opens which seems to be operating as it should. The engine has been in the truck for a year and I have only logged about 5000 miles on it since the rebuild. New radiator and heater core as well as all new hoses. I'm stumped. Any input would be greatly appreciated.
 

Diesel Dave

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Water pump seems to be pumping fine. Radiator cap is 13 lbs. One thing I didn't mention; when I was topping off the coolant I left the top off the overflow tank and noticed that after I put the new cap on the radiator (system is topped off and thermostat is open) there seemed to be pressure being released from the system through the overflow tube (bubbling in the overflow tank). I'm really hoping it's not head gasket issues but it doesn't seem to be a trapped air pocket either.
 

jimraelee

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sounds like head gasket leaking by. You can do a test where they stick a probe in the rad neck and check for hydrocarbons...
 

Devilish

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A few other things come to mind. Air bubble in the cooling system could cause issues but it's probably not pertinent in this case. My other thought is a bad fan clutch. can't cool the engine if all it does is free spin instead of engaging.
 

hesutton

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I too am concerned about this being combustion pressure getting into you coolant. With it being a 6.9, I'll also vote for a possible head gasket problem, or a crack in one of the precups in the head. The rear of the precup is a waterjacket. Any coolant on your glowplugs when they are replaced/removed?

Heath
 

Diesel Dave

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I haven't pulled any glow plugs since problem started but wouldn't hurt to check. I haven't noticed any sweet odor of coolant in the exhaust nor oil in water or water in oil but that doesn't necessarily mean anything. I know that the thermostat opens because radiator comes up to operating temperature pretty quickly. I was wondering though, what if the thermostat wasn't opening all the way? The problem seems to show itself when I let off the throttle. I revved the engine the other night and when I let off the coolant erupted from the overflow. I'm seriously not wanting this to be a major issue, if you know what I mean. The wife didn't want this project to begin with!
 

hesutton

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The wife didn't want this project to begin with!

They never do........cookoo:D

Seriously, I to hope it is something simple. But, it you are getting combustion pressure in the cooling system.........it may be a bigger fix. You do have a Ford/Motorcraft thermostat in there right?

Heath
 
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lotzagoodstuff

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Just wondering (not necessarily suggesting): can you remove the thermostat in an IDI without any significant effects? I always like to remove all the variables one at a time to see the effects. If you take out the thermostat and the problem persists, well it's probably operating ok.
 

Agnem

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The service manual forbids removing the thermostat. This would allow coolant to flow too rapidly, resulting in areas of cavitation and hot spots due to coolant not being in contact with the back side of objects. A better test would be to take the radiator cap off, and just run the engine up to temperature in the driveway. Put a meat thermometer in the coolant and make sure the temp is maintained. Look for bubbles and exhaust right there at the rad opening.
 

zpd307

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that magazine is funny as hell!!!!! i have several friends that could reallly use a subscription, links were sent.
 

lotzagoodstuff

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The service manual forbids removing the thermostat. This would allow coolant to flow too rapidly, resulting in areas of cavitation and hot spots due to coolant not being in contact with the back side of objects. A better test would be to take the radiator cap off, and just run the engine up to temperature in the driveway. Put a meat thermometer in the coolant and make sure the temp is maintained. Look for bubbles and exhaust right there at the rad opening.

Thermostat question asked, thermostat question answered.

You are truly an IDI Ninja Mel ;Sweet.
 

MUDKICKR

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sounds like a cracked head. a lot of times when they build enough pressure to put into the overflow tank that is a good sign of a cracked head. i would remove the cyl heads, and look at the head gaskets very closely. then send the cyl heads of to a machine shop and have them tested. also take the head gaskets with you to the machine shop and get his take on the gaskets. you can tell a lot when looking at a head gasket.
 

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