I am sure that there are other ways to figure this out but this is the easyiest. So me and my buddy were talking while we were changing my oil today. I have always though that the wieght on oils where 10w-30 as in that when the engine was cold it was at 30 and that the 10 was when the engine was warm. He says it just the opposite and we both are aleast we think pretty smart about cars, but this is just one thing that we looked over. His autotech teacher says that it is the opposite to. So what is it?

 

10 for cold and 30 when warm

 

if it gets really cold... go with the 5

 

W stands for winter... the lower the number the runnier or less viscous it is.

 

always thought it stood for weight, now whos the dip

 

Its winter
"The API/SAE designation for multi-grade oils includes two grade numbers; for example, 10W-30 designates a common multi-grade oil. Historically, the first number associated with the W (again 'W' is for Winter, not Weight) is not rated at any single temperature. The "10W" means that this oil can be pumped by your engine as well as a single-grade SAE 10 oil can be pumped. "5W" can be pumped at a lower temperature than "10W". "0W" can be pumped at a lower temperature than "5W", and thins less at temperatures above 99°C (210°F). The second number, 30, means that the viscosity of this multi-grade oil at 100°C (212°F) operating temperature corresponds to the viscosity of a single-grade 30 oil at same temperature. The governing SAE standard is called SAE J300. This "classic" method of defining the "W" rating has since been replaced with a more technical test where a "cold crank simulator" is used at increasingly lowered temps. A 0W oil is tested at -35°F, a 5W at -30°F and a 10W is tested at -25°F."

courtesy of wikipedia

 

and i thoguht people with a lot of posts knew more than me...
but thank you.