Hi Dan:
___It depends on what you are looking for. Amsoil used to use Mobil1 base stock and added its own additive package IIRC. Even if you could go 25,000 between oil changes, are you going to go 25,000 between changes? I wouldnt There is some recent discussion that Amsoil 5W-20 now uses Group III stock which is only partially synthetic. I am not sure as you will have to speak with an Amsoil rep to clarify Second and more important imho, you didnt purchase the Prius because it receives poor fuel economy, right? If you dont beat your automobiles, 0W-20 in a Prius will offer you not only long life; it will offer the best fuel economy available. The key difference between Mobil1 and Amsoil in regards to fuel efficiency capability is the following Kinematic Viscosities at 40 and 100 degrees C. The Mobil1 0W-20 has a much lower viscosity at 100 degrees C yet still meets all of the engineered requirements of your Prius. This lower viscosity will give you superior fuel economy. Superior may be just mpg or less but that is the reason you purchased the Prius, right
Viscosity of Mobil1 SAE 0W-20
cSt @ 40 degrees C = 33.0
cSt @ 100 degrees C = 8.4
Viscosity of Amsoil SAE 5W-20
cSt @ 40 degrees C = 45.0
cSt @ 100 degrees C = 8.9
___Amsoil does not make a straight 0W-20 that I know of.
___With that, Synthetics provide a number of superior oil performance attributes for your Prius ICE over and above regular Dino. The other side of the coin however is that they are expensive and the fact remains that there are literally tens of thousands of automobiles on the road today that have 200 - 500,000 miles or more that have never seen a drop of synthetic but simply had 7,500 mile oil changes with regular Dino. Because of Mobil1s lower Kinematic Viscosity at 100 degrees C (close to real world operating temperatures), I would stick with it for the fuel economy myself.
___Good Luck w/ whatever oil you decide to use
___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
___[email:39j46a00]
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