Another crank failure theory .... oil temperature

You're on the right track - oil breakdown due to overtemp is a symptom, not the cause. Those temps you indicate are a bit (to way) on the high side, but you've related the reason - the need for oil to cool the lower end of the engine.

An internal-combustion engine lube is tasked with the following:

Lubricate
Cool
Seal
Clean
Protect

The main cause of engine failure is heat (shut off the lube flow, the bearings spin - because the heat welds the crank to the babbitt). Lubrication prevents heat from friction. Cooling removes heat from areas where otherwise it would accumulate. Sealing prevents blow-by and increases engine efficiency. Cleaning keeps all of the first three working as they should. Protection keeps condensation in the engine from corroding expensive parts.

The cam bearing temp is too high (at least for a roller cam & lower diesel rpms) it was just a guess with a ?.

Most of the turbo heat is dissipated through the intake air and/or radiated out. Not all that much oil flows through the turbo anyway and I think its whipped to a foam from the really high RPM's.

But yeah the upper rings and crown of piston can approach 600-800F I have read and believe. Maybe not daily driving light throttle. But I can push 600-750F EGT in the wind on the interstate unloaded with my mods in the summer.

Summer time towing or an unhealthy truck could easily see 900-1000F EGT's, 200-210F coolant temps, and IAT's of 200F?. So oil being exposed to really high temps is a real possibility.

Quote:

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Originally Posted by Hubert

...Most of the turbo heat is dissipated through the intake air and/or radiated out. Not all that much oil flows through the turbo anyway and I think its whipped to a foam from the really high RPM's...

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I disagree. In my experience, copious amounts of oil flow through the turbo center section, primarily to cool it. Just look at the size of the oil return line...

I thought the return line was so oversize because the turbo's seal is more like a labrinyth type seal (because no conventional seal material will stand up the heat and rpm's). The oversize return is to ensure there is no appreciable pressure on return line and allow the foamed oil plenty of room to expand, defoam, and drain back to pan.

I could go either way I think air cools it and oil too. Not sure which does more.