In Reply to: Oil Type posted by Steve 9n on October 30, 2013 at 13:19:38:
Agree with TOH that 10W30 is the best choice for all year round application unless using at temperatures below 0 F.
Shell Rotella 15W40 diesel motor oil is quite popular on the N because is contains high level of ZDDP(zinc) for flat tappet to cam lobe scuffing friction lubricant.
Valvoline "all fleet diesel motor oil" contains higher concentration of ZDDP, 1300 ppm compared to 600-850 ppm for regular API gasoline engine motor oil mandated by federal regulations for catalylic conventers.
Most all CJ4 diesel motor oils contain ~ 1300 ppm ZDDP.
The racing motor oils produced by Valvoline and Lucas Oil do contain high levels of ZDDP.
Valvoline VR1 racing oil contains ~1400 ppm ZDDP.
Lucas motor oil contains 1265 ppm ZDDP, except API 5W30 & API 10W30.
Lucas racing oil contains between 3100 ppm to 4830 ppm ZDDP for high performance engines.
BP/Castrol HD 30, Hd 40 & 20W50 have higher concentration of ZDDP than API.
However, the flat head engine valve springs with only 20# of spring force fails to develop the friction that high performance muscle cars with high valve spring pressures have which do require high concentration of ZDDP.
I use Lucas straight 30 wt for ambient temperature between 40F to 110F with 1265 ppm ZDDP for N engine. The alternate is Valvoline VR1 30 wt.
Using a heavier 20W-50 motor oil or adding Lucus oil stablizer will reduce oil burning and smoking from worn rings, but will not affect oil pressure at normal operaturing block temperature. If the oil pressure is sufficient to pump the oil through the oil filter and governor, the oil is circulating.
If operating between 0F and 100F ambient 10W30 is the best choice and has less viscosity modifiers than 15W40, which means it will last longer.
Synthetic oil will prolong the life of the engine,(ring life), but may result in additional oil leakage through the rope type crankshaft seals.
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