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The startup rattles people complain about here are related to Toyota's VVT-i system. The VVT-i system requires fast oil flow through small tiny veins independent from the rest of the engine. Thick oil is a problem, not a solution for a VVT-i startup rattle.
Ford has been using 5w20 for over a decade on all makes and models with engines that run hard all day and night including police interceptors, taxi cabs, and Lincoln town car limos. Thats long enough to flood the internet with complaints if there were an issue.
A heavier weight oil still has purpose in an older engine that has high mileage, worn down, burns some oil. Putting thick oil in a brand new modern engine for "extra protection" is perpetuating Myth. Years behind current oil knowledge and oil technology. Thin oil has equal to or better film strength with a higher viscosity index than thick oil thanks to modern additives. To a modern engine, thick oil is like running in a swimming pool. Its hard work. More friction. More heat.
Some think because thick oil "sounds" quieter its protecting better. Myth. A thicker oil insulates better and sounds good to the ears, but thick oil = less flow = less oil = less film = more friction = more wear. Thats always been true.
Years ago thicker oil was needed to compensate for the tolerances of poorly built engines. Years ago a thicker oil was needed to gain additional film between moving parts. Years ago smoking was good for you. not true anymore. Engines are better built, oil is better refined.
02 Camry XLE 2AZ-FE 332k M1 HM 5w30
99 Avalon 95k PP 5w30
13 Malibu 16k PP 5w20
Last edited by leakyseals; 05-15-2013 at 10:59 PM.