Originally Posted by RDY4WAR
Originally Posted by 2015_PSD
Originally Posted by RDY4WAR
With higher viscosity oil than the engine is clearanced / designed for, I'm more worried about bearing temperature than oil temperature.
One would reflect the other, would it not--I cannot see how the oil would not heat up in response to the bearings increasing their temperature? Also, what engine would be clearanced/designed for a single viscosity? Not being sarcastic--just learning...
With higher viscosity, the temperature delta through the bearings will be higher. With sufficient surface area of the pan and coolant temperature through the block, the oil temp may not rise but 5*F but the bearings can be 20-30*F hotter.
There's an ideal flow vs viscosity through the rod and main bearings. Too much flow from too little viscosity risks cavitation. Too little flow from too much viscosity reduces cooling and increases hydrodynamic friction. More friction + less flow = more heat.
The ideal oil viscosity is dependent on the bearing clearances and operating oil temperature. Some hydraulic lifters are picky about viscosity as well (GM LS based engines, for example). Here's a chart of comparing bearing clearance to temperature for ideal oil grade / viscosity. The majority of modern OEM engines have between .0010-.0018" rod and main bearing clearance.
Nice find on the chart.ðŸ‘.. I've read that 10cSt was the "ideal" viscosity for bearing clearances? "Much higher than this and drag results, much lower than this and boundary lubrication occurs" in link below 👇. (what I said in my previous post).. now the question for me, at what point does boundary lubrication become an issue? 8cst?..7 or 6?
KEW Engineering