MOTOR OIL ENGINEERING TEST DATA
… The average value for Thermal Breakdown among the conventional Diesel oils here, was 255*, which is 17* LOWER than among the conventional gas engine oils I’ve tested.
The average value for Thermal Breakdown among the synthetic Diesel oils here, was 267*, which is 15* LOWER than among the synthetic gas engine oils I’ve tested.
And as you can see with these Diesel oils above, zinc levels alone do NOT establish their wear prevention ranking. The zinc levels are randomly up and down, relative to the ranking order. So, zinc levels clearly have NOTHING to do with an oil’s protection capability or ranking order. Also, anyone who has followed my motor oil testing, probably noticed that these Diesel oil “Load Carrying Capacity/Film Strength” psi values are rather low, with an average value for the whole group of only 72,408 psi. This number would put an oil for gasoline engines, only in the MODEST PROTECTION category (60,000 to 75,000 psi).
Obviously since all these diesel oil numbers are so closely clustered together with only about a 20,000 psi range (compared to the gas engine oil numbers which have a much larger range of almost 60,000 psi), it is clear that the oil companies intentionally formulated them to be in this general range.
Diesel engines of this type are made very rugged and very durable for the long haul. And in order to accomplish that, the engine’s components are designed and sized to keep the part loading at a modest level. And of course, these engines are known primarily for their impressive low end torque under boost, but NOT for their high rpm HP. All that being the case, these oils don’t need to have a higher capability. And this type of Diesel engine typically takes a LOT OF OIL. So, cost becomes a real factor when changing oil. This means that no oil company is going to make their products way better than needed, because that would make their products too expensive to be competitive in the marketplace.
RECOMMENDATION FOR MOTORCYCLES:
Most motorcycle engines:
• Make far more power per cubic inch, than car engines.
• Rev far higher than car engines.
• Share the same oil for both the engine and transmission (which subjects the oil to considerably more mechanical shearing).
• Have wet clutches that also share the engine oil.
• Often get run much harder than most car engines.
So, most motorcycle engines are far harder on their motor oil than normal daily driven automobile engines are, which results in semi-severe usage, to severe usage of their motor oil. Therefore, I recommend the following to provide the best protection:
• Do NOT follow the ridiculously long 8,000 mile oil change interval typically found in motorcycle street bike Owner’s Manuals. That outrageously long interval is Marketing driven only to reduce Cost of Ownership numbers. It is NOT what is best for the engine, and was NOT driven by Engineering.
• For liquid cooled street motorcycles, use the range: 3,000 mile oil change interval if operated aggressively, up to a 4,000 mile oil change interval if operated modestly.