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I was researching synthitic motor oils and read some data on the AMSOIL sythetic motor oil and sounds like it outperforms Mobil One even. I couldn't find a price or where it is sold and even wondered if they recommend changing the oil every 25,000 miles if that would void the car warrenty? We need nothing but the best for our Prius'
 
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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][email protected][/email:39j46a00]
 

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Thank you for your answer. I am more concerned with just using the right oil for not only MPG but long engine wear so I can be a good to the car as possible. I hear what you are saying and also believe that as long as car owners maintain their cars well, we will all see them last a long time.
 

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Toyota says that if you use synthetic oil you still must change oil at the recommended intervals. While opinions may differ on how often the engine needs an oil change with different kinds of oil, it looks to me as though Toyota is being pretty clear about the warranty requirement: no difference in required oil-change interval between synthetic and dino oil.
 

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Synthetic Oils

Yes, for some reason American automotive dealers and service centers are completely ignorant of the superiority of full synthetic oils. I have to *provide* my full synthetic oil to my Toyota dealer when I have our '03 in for the regular maintenance, they don't even have any in stock to sell me. Once the conventional drive train warranty is up on our '03 I plan to jump to oil-changes every 15k or so.

Also, Toyota was never able to answer whether or not I could use a full Synthetic transmission fluid. Since the Prius "transmission" is (AFAIK) almost completely unrelated to any other transmission design, I decided to stay with the factory fluid.

Then again, considering that we're in Michigan and the car will almost certainly be destroyed by rust in 10 years or less, maybe I'm just being stupid spending my money on synthetic oils anyway.
 

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Mobile 1 synthetic . . . from a long time user

I have used Mobil One in ALL of my vehicles and I am convinced its a superior product for a number of reasons. Since I live in Minnesota its not uncomon to have winter mornings here of 20 below zero. With Mobil One the car turns over just as easy as summer time, its not trying to warm up and move maple syrup through the engine which is what regular motor oil is like at that temperature. Another reason is reduced friction. Mobil One is superior for that also compared to regular oil. I have proven this to myself in a number of different cars and engines, they get better mileage and will turn over easier and run smoother with Mobil One. Synthetic oil also does not break down with time like regular motor oil. I have had a car sit for over 20 years and have been able to start it up just as if it had been run every day, regular oil for that length of time would have broken down and rusted the pistons. I use it in my straight six inboard/outboard boat engine, my Kawasaki ZX-10 street bike, my Dodge Durango R/T, a 3 cylinder Geo Metro, both my lawn tractors (one is over 20 years old), my motorhome with a 454, and it was in my 1969 Pontiac LeMans which I sold a few years ago to a collector who was very impressed with how smooth the engine ran and how clean it was inside. I let the dealers do their maintenance, and then I change the oil and filter myself after a few thousand miles to a high quality filter and Mobil One. I plan on useing it in my Prius also without hesitation. Nothing performs better or last longer IMHO, and I can buy a 5 quart container at Walmart for about $20 so the cost is about the same as regular oil when you consider your changeing that every 3000 miles. With the Prius engine running so little in relation to the actual mileage, I don't see any problem changing the filter after 10 or 15,000 miles and changeing oil at 25,000.
Just my 2 cents worth.... :)
 
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