Ok, my use of the word bunk may have been a bit strong but once I read through the BITOG FAQ it opened my eyes to some mis-conceptions I had. A few key pieces of information I read. I don't consider a 5W30 that much thicker than a 5W20. I'm talking about the 15W40-20W50 range as thicker.
1. 90% of engine wear is at startup.
2. Most of todays engine blocks run at 212F (ideally) and require a viscosity of 10cS. Thicker oils are at ~20cS at 212F.
3. The thicker the oil, the more wear at startup - Thicker oils are above 250cS at startup vs ~100cS for a thinner oil. Synthetics are ~40 (5W30)
4. At very high engine temperatures (302F), thinner oils drop from ~ 10cS to ~3cS. Thicker oils go from ~20cS to ~4cS - they provide no better protection.
5. Thinner grade oils have better flow and thus better cooling. Cooler engines wear less (212F vs 302F)
The cam galling was most likely due to manufacturing inconsistencies or possibly LTO. I have read this concept of Low Traction Oil that may cause accelerated galling but it is not related to thinner oils and is dependent on engine design.
I have a K24a2 and use 5W30 PP Full Synthetic.
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