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Sae and oil viscosity

Are higher viscosity motor oils of the same sae rating better for a car?


Is this a trick question? Oils of differing viscosities will be labeled with different SAE viscosity numbers. Higher viscosity ratings may cause increased friction, increase wear, and poorer fuel economy. They may circulate more slowly and reduce engine cooling efficiency.

There are a variety of needs and an oil viscosity to meet them. An 85 Cadillac with a 4.1 V-8 engine used a straight 30 weight where temperatures don’t usually get down below +30 degrees F. My 87 Mazda 2.0 used the same or straight 40 weight as an option. Put 5W anything in there and it would leak badly. The recommended range of oil viscosity should be followed for each car. Owners and mechanics routinely use the wrong specification and usually get away with it. It’s not always wise to do it, but perfection in anything is generally not found when there is human involvement.

I recommend a visit to for a good primer on oils.