Originally Posted by Dan12GT
I'm on Amsoil 10w30. I chose to go with this oil because it isn't a huge leap from the recommended and most of the time it is pretty warm here in Texas so the slightly higher weight has it's advantages with heat. I've been on it almost 10k miles and am about to change and do analysis so I will share that here
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Weight has no adavantage with heat. They all thin to about the same when warm. Startup is where its crucial that 10w-30 is thicker cold then the reccomened 5w20. 0W-30 grade oil is not thinner than a 10W-30 oil. They both have the same thickness at operating temperature. The 0W-30 simply does not get as thick on cooling as the 10W-30. Both are still way to thick to lubricate an engine at startup.
The reality is that motor oils do not need to be changed because they thin with use. It is the eventual thickening that limits the time you may keep oil in your engine. The limit is both time itself (with no motor use) and/or mileage use. The storage of motor oil in your garage, particularly mineral based oils, slowly ages the oil limiting its use later. Do not store huge volumes of oil in your garage that is exposed to extremes of temperature.
When you drive that car down the road mid-winter in upstate New York or mid-summer in Florida the engine and oil temperatures will be around 212°F. But your Florida vacation is suddenly altered by a hurricane. You have to get out of Tampa, but so do a million other people. It is now 95°F and you are in a snarl. Everyone thinks they need a thicker oil for this situation. This is false.