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The relationship between EGTs and engine temps isn't something I thought about a lot before, but I can see how that will be critical. I will definitely use the high rpm/low throttle technique. In the past I have always used full throttle up grades.
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Want to absolutely avoid full throttle and boost for sure. As 745TG said and I have also experienced, you can cruise at moderate steady-state load safely for a long time... but if you spike the load and EGT suddenly it can make a big difference in engine temp even if only for a few moments. If your strategy is high gear and full throttle up a grade then I'm not surprised you're accustomed to watching the temp gauge rise routinely. I'd aim for a balance point that lets you stay on the road but keeps gauge in the dead middle, and plan to back off as soon as it starts to rise, if you want the most conservative possible approach.
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I have blown head gaskets twice in the past on D24s, but both times there was a total loss of coolant, rather than simply getting warm with the coolant remaining liquid... and both motors had fiber gaskets. My current motor has an MLS gasket
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It's no problem to blow the gasket on a motor that still is full of coolant... ask me how I know. Get it hot enough where the head starts warping or the bolts stretch and you're there -- you start with a small combustion gas leak and pretty soon after that the motor suddenly shoves about 3 gallons of coolant out the top of the expansion tank -- game over. Doesn't help that the hotter the motor gets, the less ignition delay there is after start of injection, so you effectively get a little more timing advance when you're approaching the limits for heat -- increasing peak combustion chamber pressures and making gasket failure all the more likely. The MLS gasket is not indestructible either; I have had to replace them before. Doesn't change the rules in terms of what is acceptable and what is too hot, only means that it's not subject to failure just by being in the motor long enough to erode from normal use.
