My wife just purchased Toyota Prius and I was surprised to read its manual. It is calling for 0W-20!! We live in California. I looked up my 1973 Nissan Sentra service manual and it includes "Oil viscosity and ambient temperature" chart. According to that chart, 0W-20 covers between 0 to 60 degree only. Here we often see >90, in fact, today the temperature went up to 95. How can 0W-20 oil protect the engine? I have been using 10W-40 for all of my cars and had no issues at all. 0W-20....?! Did anything change so that now 0W-20 can protect engines even under 100 degree ambient temperature?

They probably use 20 to boost mpg ratings. Also, doesn't the prius "shut off" at idle, like at stoplights, and then restart? This is probably considered a cold start, and uses the lighter viscosity to reduce start-up wear, and ease resistance on the starter. My guess anyway.

Engineers are specifying thinner and thinner oil. If their manufacturers are willing to warranty the engines using this lower viscosity oil, who are we to question them? We are moving towards a time where water will be the lubricant of choice and oil will be obsolete.

Metal-to-metal contact is mostly prevented by additives rather than the oil itself. The oil is becoming more of a medium to spread the additives than previously, which is why it will someday be replaced by water.

* Last updated by: Danno on 9/22/2015 @ 6:14 AM *

Yep, run what it's calling for. Tolerances are tighter than ever which is one reason for the thinner oil. Throw some 20w50 in there and watch your engine blow up!

I take some 90/120 gear oil and cut it with kerosene. It "clings" to the machined surfaces to prevent dry startup conditions.

I bought my son a new Mazda 3 and it takes 0W/20 also. Seems thin to me too but I always use what the maker says to use.

I bought my son a new Mazda 3 and it takes 0W/20 also. Seems thin to me too but I always use what the maker says to use.

the prius "shut off" at idle, like at stoplights, and then restart

I checked with some Web site and this seems to be the main reason for the thin oil. I guess I will stick with what Toyota recommends and use 0W-20.