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Old 07-17-2019, 02:16 PM   #11 (permalink)
hayden55
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Join Date: Dec 2010
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Sport Utility Prius - '10 Toyota Prius II
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Not a ton. From class we had a little tribology portion in mechanical system design and the big weights weren't hugely different. I'm sure you could find a "temp and viscosity thickness" chart and compare different weights at x temp for your reference as it relates to your transmission. Main take away: gas mileage will only vary a small percent wise, but the friction goes up and decreases the life cycle rating if the bearing/wear tolerances are designed to maintain a certain gap /psi rating with the spec weight at x temperature and you put in a thicc er fluid or cool the fluid too much. Think: Toyota doesn't recommend 0w-20 in their 0w-16 designed motors.

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