Wayne:
As you suspected, gas mileage is the reason for the 5W-20, year round. This helps out slightly with the frictional losses associated with the crank plowing through the
oil in the crankcase and other frictional loses associated with
oil viscosity. It is a result of the CAFE(Corporate Average Fuel Economy) requirements placed on the manufacturers by our bureaucrats in DC. The fuel benefit is not much, but everything helps when the heat is on.
5W-20 is ok for the winter, but I stay with 5W-30 year round in my regular cars. It's a good compromise for both summer and winter.
I too have seen bearings with 100,000+ miles look like new, but the type of driving and ambient conditions are a big factor along with
oil and maintenance. What you want is quick flow to all parts of the engine, thinner oils do that, then you want the proper viscosity at operating temp. Without multi vis oils, that used to be a compromise, but no so today.
However, at risk of sounding like a broken record, PAO's have better flow characteristics(viscometrics) at low temps than do mineral oils, it's called borderline pumpability and viscosity index. PAO's simply have better numbers in these areas than Group II basestocks. Group III stocks approach the PAO's with respect to VI and other parameters, but still they are not as good, in these and other areas.
We are getting close to the Castrol Syntec debate.
Jerry
Hybrid Mode
