abnormal pressure in the cooling system

[bennetr]

1984 F-250 6.9L diesel. Within minutes of engine startup and long before the engine is warm, there is a tremendous amount of pressure in the cooling system. Top radiator hose is rock hard, but once your release the radiator cap it will collapse and then the pressue builds again once the cap is replaced. The overflow resevoir bubbles even though temp gauge reads normal. Engine runs hot but not extreme. Top and bottom hoses replaced along with thermostat and radiator cap.
Local folks tell me it is most likely a head gasket and or crack head, which is allowing combustion gases into the cooling system. Ready to start tearing down the engine but would like some advice first.

[ModMech]

Yup, headgasket. VERY common with the 6.9L engine, and somewhat common (not entirely unexpected anyway) with the early 7.3L.

Be glad it's not a GM 6.2/6.5L. After 20+ years they STILL have headgasket problems.

[Garland]

Anything similar to that happen with the '80 302s? Mine runs extrememly hot usually but sometimes runs fine during the day. I also see bubbles in the overflow tank sometimes.

[97chevyman]

try new cap and thermostat otherwise new pump.

[bennetr]

are you suggesting that my problem could be a water pump and not a head gasket? I am just about ready to remove the heads but will hold off if the water pump may be the culprit. During tear down I did notice water leaking from the gasket at the bottom of the water pump and planned on replacing it while I am working on the engine.

New question, can the heads be removed with the exhaust manifolds still attached? What about leaving the intake manifold in place? looking at it, it seems like I can lift it out, without complete disassembly. Can it be done or just wishful thinking. The manual shows alot more that what it looks like needs to be done.

[mikeinphilly]

your lookin at a pretty entailed job take the intake off,yes save your self alot of headaches and just remove anything thats in the way you might find it easier if you go out and get ziploc bags with labels and mark everything ,like intake bolts head bolts etc.

[Glamisman]

It has been 7 days since you were going to take the heads off... what did you find?

[bennetr]

I have successfully removed the heads. We learned some valuable lessons. First read the sequence in the manual and follow it! We forgot to pull the oil dipstick tube and had a heck of a time trying to get the head out, until we saw it still in place. We were able to leave the exhaust manifolds in place. You must first loosen up the heater core box in order to get the rear head and manifold bolts out.
I have not seen a blown gasket before and took them into my uncle's shop. There were some areas that were candidates. With the higher combustion pressure in a diesel, it would not take much to allow the gases to pass into the cooling system. Heads look good, a couple valves had a little carbon. Pistons, cylinder walls seem fine. Will pour some solvent onto the vavles and should get an indication on whether they are seating properly.

[bennetr]

I will do a home version of a magnaflux on the heads and look for cracks. With the engine tore down, I am replacing the water pump. No oil in the coolant, no coolant in the oil. After a through cleaning of the engine and different pieces, plan to put it back together over the next several days. Using a cherry picker to reinstall, brute force to take them out. Son works for NAPA, DISCOUNT!!!

[rangerreb]

I haven't pulled one down yet that did not have a cracked head. Sometimes they can be repaired. I have had to purchase new or used heads before.

[steve longo]

Originally Posted by bennetr

1984 F-250 6.9L diesel. Within minutes of engine startup and long before the engine is warm, there is a tremendous amount of pressure in the cooling system. Top radiator hose is rock hard, but once your release the radiator cap it will collapse and then the pressue builds again once the cap is replaced. The overflow resevoir bubbles even though temp gauge reads normal. Engine runs hot but not extreme. Top and bottom hoses replaced along with thermostat and radiator cap.
Local folks tell me it is most likely a head gasket and or crack head, which is allowing combustion gases into the cooling system. Ready to start tearing down the engine but would like some advice first.

get an air compressor, buy or make a air chuck to glow plug adaptor, pull glow plugs out. Install air chuck adaptor. Turn tested cylinder to top dead center at combustion stroke. fill cylinder with about 60 psi air. Fill radiator to top. look into radiator for bubbles. Do all cylinders one at a time. Make sure that the tested cylinder is at exactly top dead center or engine will rotate away fromTDC. this is cheap and will cut out a lot of guess workand time