5W20 Oil

1) >90% of all engine wear occurs between the time you turn the key and when full oil pressure is developed. Thinner oils flow faster, pressure builds faster, hence less wear.

2) It takes energy to pump oil, the thinner the oil, the less the energy, the better the mileage.

3) Pumping oil heats it, the thinner the oil, the less energy it takes, the cooler the oil remains.

4) Oil's ability to lubricate is based on flow (as above) and film strength. Our modern full synthetics and synthetic blends have higher film strength and therefore lubricate much better the thicker, conventional oils.

The guys are right... follow the manufacturer's oil type and weight recommendations and you not only get better mileage but longer engine life.

I agree about running mfg recomend weights.

When I was researching what to use in my new 7.3 PSD, I decided on Chevron Delo.

Since that was so good on diesels, I tried Chevron Supreme 10w30 in my Chevy 4cyl. I picked up 2mpg on the first tank and 4mpg on my second tank and thats where it's stayed for the past 18k miles, plus 4mpg.

I've used Quakerstate for the past 40yrs. When I switched to Chevron Supreme my oil cleared up after a couple changes and looked like the factory oil did at change time, dark amber. The Quakerstate was black at 2/3 of change mileage. I'll never run Quakerstate again!

Told my son about the fuel mileage gain with the CS, so he changed over on his Ranger and got 2mpg better.

T_Bone

On smaller engines the heavy oil will hold the lifters or whatever type of hydralic cushion is used in the valve train in such a way the valves don't close when they should.

ANother just ask is the fella that tried running 20-50 in his 6.8 V-10 Ford RV cause it was what he used in his old 460. Nasty valve train.

Anyway, use what the owner's manual or the filler cap says.

The bearing clearances are very tight. The large molecules of a thick oil don't flow into the bearing space well, and the bearing runs comparatively dry and burns up with the heavy oils.

The thin viscosity oils with their smaller molecules are able to flow into the tight bearing space, and provide lubrication.

Oil viscosity is a phenomenon driven by the formation of hydrogen bonds between molecules within the oil, not by the size of these molecules.

The size of the molecules of the constituent hydrocarbons of a thick oil and those of a thin oil is about the same.

Molecules are very, very small compared to bearing clearances. You can measure the diameter of an oil molecule with a simple experiment like this one:>Link

A>Link "tight" bearing clearance of .001 inch is more than 10000 times greater than the diameter of an oil molecule.

It always gets me how people know more about these things than the guys that designed and build them. Use the recommended oil.