Join Date: Dec 2010
Location: Epping, NH
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EDIT before I post:
I see there are answers already posted, but this post took way too much time to type, so I am posting it anyway.
The way that the engine was manufactured, they installed a style of head bolts which are called Torque To Yield (TTY for short). As those bolts are tightened, they are designed to stretch a little bit.
The problem with that style is that they can still stretch more if cylinder pressures are higher than expected. When this happens, clamping force on the head is lost, the cylinder pressures lift the head off the block and the head gaskets blow.
What typically causes this to happen on the 6.0 is a culmination of a few things.
First, the block is cast in the factory using a sand mold. They (the manufacturer) does their best to get all of the sand out of the block, but some of this sand actually becomes part of the block. Over time (and wear) this sand can work its way free from the metal surfaces. This usually happens within the cooling system. This is part one.
Next, this casting sand will collect in the oil cooler that is internal to the engine. The oil cooler is a liquid/liquid style cooler, which means coolant and oil flow through it in alternating layered passages. This particular oil cooler has both liquids entering and exiting through the top of the cooler. Any and all debris present in the coolant will settle in the lower portion of the coolant passages, causing a blockage.
Now, we will talk about how the stock coolant that is used figures into this as well.
The Ford Gold coolant requires frequent monitoring of the additive package. The additives combat cavitation, corrosion in the cooling system and the freezepoint of the coolant. The heat that the egr cooler sees depletes the additives rapidly.
Lets stop here for a second and discuss what the egr cooler is, what it does and where it is. The EGR coolers job is to cool exhaust gases before they are reintroduced back into the engine for emissions purposes. The flow of cooled exhaust gases is controlled by the EGR valve. The coolant coming out of the top of the oil cooler is directly fed to the egr cooler. The egr cooler is connected to the exhaust system just previous to the turbo (as far as exhaust flow goes) on the passenger side. The exhaust gas temps can reach 1000°F or more fairly easily.
Now, back to coolant. The coolant, once the egr cooler heat has depleted the additives, can create a goo within itself and allow rust scale to form on the walls of the cooling system. This junk and rust scale gets caught in the coolant passages in the oil cooler. This plugging will slow the coolant flow coming out of the oil cooler, and the slower moving coolant going through the egr cooler allows the egr cooler to overheat. Continual overheating of the egr cooler causes it to fail, and begin to leak coolant. This coolant will "stack up" behind the egr valve, waiting for it to open. Once the valve does open, your engine gulps down a drink of coolant. This coolant entering the cylinders is what will raise the cylinder pressure beyond what those stock TTY head bolts can withstand, they stretch, the heads lift, and your head gaskets are toast. There are other consequences to a failed egr cooler. The coolant can also flow out into the exhaust stream while the engine is running, and flow through the side of the turbo that the variable vanes are. Mixing coolant, soot and heat will create a substance that will interfere with the free movement of those vanes. The end result of this is "overboost" or "underboost" conditions. Overboost by itself could possibly pop the head gaskets. Either way, it will run like crap, and you should see white smoke coming out of the tailpipe.
When the truck is shut off, you are still not "out of the woods." The leak is still leaking since the cooling system is still under pressure. The coolant will flowout of the failed egr cooler and flow down the exhaust and enter the exhaust manifold on the passenger side of the engine. This will result in a big cloud of white smoke soon after you start the truck, and it could effect how the truck runs at start-up as the coolant gets pushed through the turbo. You could also see water exiting the tailpipe.
When the truck is off, should your egr cooler leak enough, the coolant could enter the cylinders on that side of the engine through whatever exhaust valves are open when the engine is switched off. When this happens, the engine hydrolocks.
All of the above is usually what causes the head gaskets to blow.
Most of the signs of a failed egr cooler and popped head gaskets are the same, but head gaskets will leak compression from the combustion chambers into the cooling system. The pressure will eject coolant out of the degas bottle (where you monitor/add coolant). Cooling system pressures with blown head gaskets will exceed 16psi. The cap on the degas bottle vents pressure above 16psi, and this pressure will push coolant out.
Once all of this happens, NOBODY wants to put the TTY head bolts back on the engine, (other than FORD during warranty repairs) since that type of fastener isn't the best solution. They use head studs. Head studs screw into the block of the engine, then the heads are slid down onto them, and a washer/nut is what applies the clamping force. The studs do not stretch due to their strength.
I think that just about covers it all. If I missed something, someone will fill it in.