I found this image of a Prius manual from South America (nicaragua). It's pretty surprising what Toyota recommends in non-US or EU regions. I didn't think the car could run such thick 40 and 50 weight oils. To summarize: 20W-50 may be used in the S.A. Prius if the temperature is above 20F 15W-40 above 10F 10W-30 above 0 F 5W-30 or 5W-20 in all temperatures http://i1239.photobucket.com/albums/ff515/zeuloa/photo2.jpg
You bet it will. But the thicker the oil, the greater the load on the engine. So in order to get the best fuel economy, lighter oil is used.
The Australian owner's manual doesn't even list 5w-20 as a recommendation. Only 5w-30 or 5w-40. That makes me wonder why Aussie Priuses don't have the 20 weight option
I'm not seeing the word "Prius" in that image. (I'm not disputing different regions spec heavier oil, and the image could be legit, just saying.)
There's no reason to question it. That Australia and South America use thicker oils is a well-known fact.
Shouldn't one consider changing to 5W30 after the warranty period? I don't think the thicker oil would have much effect on mileage.
Remember the W in the oil spec. That means at 0C the oil acts like the first number weight wise, and at 100C it acts like the last number weight wise. That is, for 20W50 at 100C the oil is as viscous as 50 weight oil would be at 100C. So it doesn't seem that heavy when you pour it. It pours like 20W at room temp (or perhaps slightly thicker). Keep in mind the oil will run at temps almost always higher than the coolant, so the second number will probably be more important than the first once the engine is warmed up. The first number will impact ease of starting, which is not a problem for a Prius with a 20 HP starter motor running from 570V three phase power. The second number will impact fuel economy. In the US there are rules regarding that. In some other countries not so much.
In the US, a manufacturer has to the use the "specified" oil during the EPA test. So, if you want to use 0W20 to get the best test result, then this has to be the recommended oil. I'm not suggesting that 0W20 doesn't provide adequate engine protection, but other weights seem to work as well according to non-US specifications.
