So a smaller bearing clearance requires a thicker viscosity oil? I thought that that was the other way around, or am I reading this worng bruce?
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So a smaller bearing clearance requires a thicker viscosity oil? I thought that that was the other way around, or am I reading this worng bruce?
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The biggest single advancement in diesel engine life came about 20 years ago when diesels transitioned from a straight 30W diesel engine oil to 15W040 multi-viscosity oils. On highway class 8 engine life when from around 300,000 miles between overhauls to sometimes approaching 1,000,000 miles without having to change main and connecting rod bearings..
i.e. the affect of having that 40W cushion enabled main and connecting rod bearings to achieve a much lower wear rate.
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And yes, those engines that did use 40W did have a longer life except for those engines in the northeast who experienced spun main bearings on cold weather start-up. i.e. the use of 30W in the north/northeast was a happy medium diesel engine oil.
Moreover, the introduction of not only the 40W operational viscosity but also the 15W cold flow characteristics on start-up was a huge operational plus. Very shortly after the widespread use of 15W-40 multiviscosity oils, I stopped seeing crushed connecting rod bearings (30W), scarred and spun main bearings from cold weather operation, scarred and gouged camshafts. i.e. a number of early engine overhaul causes were eliminated and engines began living longer.
In a lubrication engineer's training from day one, it is viscosity, viscosity, viscosity. And in engine oil it is "optimum viscosity"... When maximum engine and component life is the goal.
George Morrison, STLE CLS