You're totally wrong there. Head gaskets have a few different failure points and one of them is just looking coolant out the block onto the outside. I've seen this several time. It can also leak only oil to the outside of the block, coolant to the cylinder, oil to the cylinder.
There are more obvious failure points, but there are many more than just exhaust into the coolant.
I agree w/ you, I over generalized, but not totally wrong since the dowell info is totally correct - lol.
I will agree that all failure modes are possible. HOWEVER, the original post indicated that head gaskets sealing will eliminate coolant leaks. This is the statement that is totally wrong. Because of this, I make the revised point - BY FAR, the most common issue with head gasket leaks is combustion gasses leaking into the coolant.
Again - I agree that all failure mechanisms are possible (and have happened), but the combustion gasses are MUCH higher pressure than the coolant or oil and therefore the most common failure is combustion gasses into the coolant. Yes you can get some coolant into the cylinders on intake strokes, yes you can see external leaks, but whenever head gaskets are weakened for whatever reason, most commonly the issue will be seen by high pressure combustion gasses leaking into the coolant. Coolant and oil pressures are certainly no higher than 75 psig off of the pump discharges (spec for LPOP discharge regulator). Even hand tightened connections can seal against leaks under these kinds of low pressures as opposed to the high pressures generated in the cylinders that require highly torqued bolts/studs.
Some of these combustion gas leaks into the coolant do not cause puking right away, but they do eventually lead to big problems, even when the leak is small. That being said, there are plenty of cases of oil coolers plugging without head gasket leaks. Also, there are cases of EGR coolers failing without oil coolers being plugged. So again - practically anything is possible
Ford has done investigations and shown that COMBUSTION GASSES GETTING INTO THE COOLANT WILL PRECIPITATE SILICATES. Therefore this raises the question:
Which comes first?
- bad coolant plugging the oil coolers, then causing EGR coolers to fail and then getting coolant into the cylinders and popping head gaskets?
- OR -
- Is it slight head gasket leaks letting combustion gasses get into the coolant that BEGINS the silicate "drop out" process and sets the previously described events in motion?
IMO the answer is both.