I was at canadian tire the other day and I was looking at castrol syntec oil. I was going to buy some for my car,butI only saw 5w-20 and 10w-30. This is wierd, because I was told, and have always put in 5w-30 into my car. What should I do? and what the h*ll do the numbers mean? what does the 5w and 10w stand for? And what do 20 and 30 stand for? I think I was told once that one is more viscose (or lighter), but I don't remember...

 

Im not sure wat all the numbers mean but i have always heard 10w-30 in the summer and 5w-30 in the winter but im not really sure soo. . .

 

Well here's a funny story. I went back to canadian tire and I asked them if they had any 5W-30 castrol syntec... it turned out that they forgot to stock the shelves... hah

 

I love this site: http://auto.howstuffworks.com/question164.htm

 

they stand for the weight of oil per a certain amount, a heavier weight equals a thicker oil. Use thicker in the summer and thinner in the cooler months