Ok I was talking to my cousin who mechanics a lot over the holidays. He works for a municiple garage and sees a lot of engines. Recently 5 broke 6.5 cranks over a couple of weeks/months. He said oil temp may be an issue and the bearing and journals are getting too hot. I asked him what he thought about the harmonic balancer failures and he did not comment on the appearance of HB on these particular failures but he mentioned Fluidamper and importance of a good HB. He mentioned oil passage size at the front cam bearing changed but I missed the specifics, as I pointed out the oil spray coolers and increased oil flow for 97+ engines.

It has always struck me that the 6.5 has so little oil capacity compared to the other pickup diesels. But have read many times cylinders have very little wear with many miles on the engine so I let it go and figure oil is probably adequate.

I use to think oil should get to 212F then a few threads a long time ago and several hours of reading changed my mind. A new thread started me thinking again and I wonder just how hot does oil and bearing surfaces get in the engine? I have read too much to find it all again but thought I saw a blurb about cam journal bearing getting really hot (can't find it again but 300-400F I think). And of course the piston face is seeing really hot temps up to 3000F combustion temps and EGT of up to 900-1000F are measured towing. Blowby will be related to EGT and I never really thought about just how hot the upper ring and oil is getting. But apparently it lives ok.

Back to the crank and main bearings. After reading I am now curious just how hot do you think the crank and journals are getting locally? I've never heard anyone say the crank was blued or changed color due to heat but after failure its hard to determine the last few moments and chain of events. I also haven't read of many spun bearings but maybe its not getting hot enough to gual but still hot enough to encourage failure???? I have read the turbo will choke or oil will coke if shut down hot. I am guessing mains and cam bearings are not that hot and/or can dissipate the heat better. I imagine the continuous flow keeps the oil from cooking but I am starting to think it momentarily gets really hot at some points in the engine.

Just food for thought.