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the end of that article is the key. as long as the oil smells good and is clear, it's good. once it turns dark, it's done. the problem with dino oil is that it turns dark very quickly, especially on a higher mileage engine, due to carbon build up. further, the polymers in dino oil do not react as well and expand as far as those in synthetic oil, especially when the oil is dirty. so, while you may think you have a 20/50 oil in there on your 100k mile 944, you likely have more like a 20/30 after the first 1500 miles following a change, whereas the synthetic oil will maintain its ability to reach the higher viscosity.
if you change your oil frequently enough, you can run just about anything, as long as it can handle the heat range of operation. if you only street your car, you can get away with a much lower viscosity oil than if you track it. the lower the viscosity, the easier to start, the more quickly it gets up to temp, and the less resistance on the moving parts, making the engine rev more freely, thereby increasing fuel economy.
it is a huge mistake to run a 20/50 oil on a pure street car. there is no reason for it. the oil temps will never get up high enough to need it. all it is going to do is make the engine work harder, run hotter, and get poorer fuel economy. i used to run by the old "if it's thick it's good and if it's thicker it's better" philosophy. however, when i switched from a 20/50 to a 10/40 i immediately noticed that the engine revved more freely, and my operating temps DROPPED. my oil temp went down a full 5 degrees. i then switched from redline to amsoil which had a higher upper end limit, and i was good to go, with all the protection i needed, with none of the drawbacks of the heavier oil
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