Toyota USA recommends 0W20 in the US manual, no distinctions I think. Toyota Australia though, while still recommending 0W20, mentions various other weights, leaves it more up to the customer. Bottom line, I think you need to weigh the various recommendations, and weigh other factors too, including your climate, driving conditions. Sustained high speeds in a hot climate, I might go to 5W30. More sedate driving in a hot climate, maybe 5W20?
I am a very quiet driver , having an egg under my right foot. And live in a more temperate climate than Arizona. I guess 0w20 will be fine. Thanks a lot for the answer.
For Gen2 (2004-2009), in the USA, 5W-30 is the recommended grade. In one case reported here (some years ago) a PriusChat member wrote to Toyota USA to ask if it was OK to use 0W-20 in a Gen2 Prius. Toyota USA said it would be OK if you maintained 5000-mile drain interval. I personally would not use 0W-20 in a Gen2 because I feel Gen2 gets a certain higher level of fuel contamination in the oil, so I don't want my lube oil to lose all of its viscosity. The only reason to go to 0W-20 would be to eek out a few more miles per gallon, but at some age of the vehicle, your goal should probably change to being kind and gentle to the car.
There is nothing on the cap and we, in Europe I mean, tend to be told to get thicker oils. Well, it's not like I am going to be on the autobahn running at 200km/h. Anyway. I put 0w20 fully synthetic in. Already got 0.4 l/100km lower consumption. That's 10% less than before. At $7 a gallon for gas here, I think it's justified. It pays for the oil change and then some. And BTW, that oil costs $18 a liter. Previous oil was 10w40. As for dilution, I don't do short trips with it. There is very little gasoline smell when changing the oil, so, very little dilution. Why the heck do I keep living in this place with these prices?
As far as I know 0-20 is NOT suppose to be used in a Gen. 2 Prius. Here in the USA 5W-30 is the recommended oil. As always you should follow what the owners manual states. If you don't have a paper copy you should be able to get it online.
I can appreciate the improved fuel economy with the use of 0W-20 vs. 10W-40. I had tried using 0W-20 in my 2004 several years ago and that showed about 5% improvement compared to 5W-30 oil. However I also found that oil consumption increased significantly so I reverted to using 5W-30. 0W-20 was not recommended by Toyota in the US until the 3G Prius (2010 model year and later) was released. 5W-30 is the recommendation for Classic and 2G Prius. I recognize that elsewhere in the world, a wider viscosity range is allowable based upon ambient air temp.
After so much time, an update is in order. Did some trips in the summer where the car was loaded on hilly terrain. Fuel consumption seems to be 15% less than with 10w40 in these cases. I would expect that the hot weather (about 100 F) would lessen the difference, but it got bigger than average, probably because of the higher load. There is more oil consumption, that seems to increase with the load, but fuel works out to be much more expensive than a little burnt oil in Europe.
