I'm interested in others' thoughts on this. First my theory:

As the proud owner of 3 apparently good #14 heads, I have leaned toward heads from properly maintained cars, with minimal boost. So far I'm batting 100 (whatever that means), as it appears that all three engines have good heads.

The reason I look for minimal boost, is that I suspect metal fatigue as the failure, and not necessarily from thermal cycling (but it can be a contributor).

The more boost, the more bang (Alda regulates fuel enrichment based on boost pressure). The more bang, the more stress/strain on the areas surrounding the bang. More heat also, so I'm not sure how to involve them both in the matrix, other than they are in direct proportion to each other, or more boost = more enrichment = more heat & more pressure.

The later head castings were reinforced around the water jacket according to the FSM. Whether this area fails due to being too weak overall, or merely being the weakest point and therefore the stress concentration of the part I'm not speculating, either could be true.

When in the casting business, one of our clients made Police cars, and we were quoting intake manifolds for that engine line. The Engineers at that automaker specified a PA6/6 (nylon) with glass fill, worked pretty well for the regular engines. For the Police car, the extended full-throttle runs caused the intake manifold to fail in the water jacket crossover, we found water pressures around 130psi (pressure pulses) at full-throttle were common. Needed to go to a cast intake manifold.

So, in a diesel engine, pressure pulses are even higher, and a weak point in a water jacket, especially sharing a wall with a combustion chamber, would be subjected to a great deal of shock and stress both thermal and mechanical.

In addition, I'm wondering about how cavitation pitting might affect the head combustion-water jacket interface. I know how it affects cylinder liners, and how important nitrates and molybdates are to that surface, could it also lead to thinning of the water jacket wall in the head? If so, would owners' and mechanics' almost universal lack of understanding of the coolant needs of a diesel engine have led to many of the failures?

I'm interested in others' expert opinions and discussion on this.

__________________

Gone to the dark side

- Jeff