Originally Posted By: kschachn
Originally Posted By: ZeeOSix
Semantics ... they both are conveying the same basic message. The SAE rating (Xw-Y format) is describing how the oil flows cold and hot (ie, what's the viscosity at 40 C and 100 C). That article isn't real technical either because of the statement "
10W refers to the low-temperature viscosity ("Winter"), 40 refers to the high-temperature viscosity ("Summer")."
The "high temperature viscosity" is measured/classified at 100 deg C (212 F), which can be achieved any time of the year inside an engine, not just in the "summer". There is no "S" in the rating, therefore no such thing as a "Summer" rating. The "W" (winter/cold temp) viscosity is measured/classified at 40 deg C (104 F) - hardly "winter". The Amsoil article does a better job at explaining it IMO.
I think your semantics upstage mine, but OK.
There is no SAE 0, nor SAE 5, nor SAE 10, so to say it "performs" like one at the specified temperature makes no sense. It's not how it works, and it just contributes to the idea that "0W" oil is "thin" at cold temperatures when in fact it may very well be thicker than a 5W oil depending on what temperature is being compared. It contributes to the mistaken notion that you start off with "SAE 5" oil and add viscosity improvers till you get a 30 weight to make 5W-30 oil. It misleads the reader by oversimplifying something that in reality isn't that way. That is what I object to, but if you like that comparison you can stick to it as apparently a lot of people seem to want to do.
Like I said, some semantics involved. You're taking them too literally. All they are saying is that a multi-grade 5W-30 oil will flow at 40C to receive a viscosity "grade" of "5" and will flow at 100C to receive a viscosity "grade" of "30". See chart below.
The "W" behind the first number just means it's viscosity classification/grade is based on how it flows at 40C. The second number indicates it's viscosity classification/grade based on how it flows at 100C ... it's not rocket science.
0W is thinner at 40C than a 5W, and 5W is thinner at 40C than 10W, etc ... that's all the SAE rating is saying. The SAE rating is specifically defined at 40C and 100C so the rating makes sense for comparing different multi-grade oils. It's only "misleading" to people that don't understand the basic concept of the multi-viscosity rating.
