Originally Posted by stlxfire
While picking up some 0w-40 Mobil 1 (still on sale at Advance Auto $4.77). I was told that the 5w and 0w was actually the same thing. He suggested that 0w would have 0 viscosity. Is he an idiot or is there anything to this? I've never heard anything like this before.
check out this link that describes the SAE grades:
http://www.texacoxpresslube.com/carc...viscosity.html
0w can be pumped and cranked at a slightly lower temperature than 5w. that is the biggest difference. the w component of the oil's viscosity is all about getting the engine started when it's -40 C (and maybe even -40 F, lol). for a multiviscosity oil, the 2nd rating number, e.g. "40" is what matters once the engine is starting to warm up. note that at high temperature (100 C) the viscosity must only meet a minimum threshold to meet the specified grade for "w" lubricants. the specification for kinematics viscosity is the same for both 0w and 5w, which might be what the advance guy really meant to say.