Basically, engine oil is blended with base oil and additives.
The rule of thumb is that the higher the difference between low temp. index and high temp. index, the more additives you need to cover the change in viscosity. For example, comparing Mobil 1 SAE 15W50 and 5W50, you can get lower viscosity at room temperature with 5W50, with the expense that the lubricant is actually requiring more VII (viscosity index improver) to set. The VII is then the key ingredient to keep the lubricant's viscosity, and hence the oil film stability. VII is one of the easiest members to be decomposed by heat, and shearing force in the engine..... So, you'll have the lubricant get earlier deterioration....
So, good lubricant requires GOOD BASE OIL, to minimize the dependence on additives.
And don't be fooled by the API SM standard, NOT all lubricants are made the same although they can fulfill API SM standard.
The aim of API SM is actually to REDUCE POLLUTION..... It is not talking about increasing performance of or protection to engine. Real demanding lubricants can never achieve API SM requirements as at least one of the additives required for engine protection, such as zinc compound, can never be reduced.
So, watch out and choose..... |
