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Old 06-16-2009
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Denise, the "SAE" ratings are only relevant to one thing: How quickly does that oil flow through an SAE funnel at a specified temperature? Literally. That's all they measure, one temperature cold, one temperature hot, which is why some of them have a "W"inter rating as well as the single hot rating.

SAE ratings don't mean much.

The API "C" ratings for diesels ("C"ompression engines), and the "S" ("S"park)ratings are more important. A grade CD oil meets later specifications than a "CC" rated oil, and is obsoleted by a "CE" rating, etc. Same thing for the "S" series, the later in the alphabet that the second letter is, the newer the specs are. Sometimes that's not very relevant, but usually the later letter is the better product.

All oils with the same ratings aren't the same, but it is hard to find meaningful ways to compare besides reputation or brand name. Synthetic oils generally are built to higher standards, with added ingredients for better lubrication like molybdium sulfide dust, and the ability to provide "thin film lubrication" which protects your engine bearings during starting. The SAE specs don't rate those qualities at all.

So...any brand name you have faith in, that meets or exceeds the specs for your engine and the operating temperature range you will be running it in. If you want some fun, spend $25 on sending out an oil sample for testing once a year. The tests will show you if there is fuel or water or dirt contamination in the oil, along with trace metals that can warn you of bearing failures, etc. way before they are going to happen. Water contamination can come from simply not running the engine long enough and hot enough to cook off the normal condensation that forms in the oil, most of the sampling companies will tell you how to interpret their results.
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