5w-30 and 10w-30 are basically the same thing, you can even use a 0w-30!
when they are hot they will all act damn near identical.......
I don't know why they still sell 10w-30.... I think its because so many old schoolers still buy it and they make money off of it. Another factor is its cheaper to make for the oil company, if they sell all their product at same price, they make more money off of you when you choose the 10w-30 over the 5w-30. 10w-30 is also a popular quick oil change place grade of oil. Again, the almighty dollar. I can get 55 gallon drums of oil from a distributor that will remain nameless. A 5w-30 55 gallon drum of Formula Shell is over 200 bucks more then a 10w-30 55gallon drum of Formula Shell
if you have been putting 10w-30 in your car, 5w-30, or 0w-30 will have no adverse effects
I have used 0w-30, 5w-30, and 0w-40 in my SHO
lately, all synthetic oils..... I stick with the Mobil 1 0w-40 now for a few reasons, none of them is worrying about engine wear
remeber, the smaller the number on the winter rating, the better start up protection you have when the oil is under 180-200 degrees.....
don't confuse the first number with the second, they have no relation. If you wanted a hard number to look at for the first value that relates to the weight of the oil, then your oil bottles would look like this
this is HIGHLY estimated, just for example
0w-30 would be say 60-30
5w-30 would be say 70-30
10w-30 would say 90-30
a 0w oil at room temperate is usually THICKER then a 20w-50 at operating temperature. You want thinner oil........ I would never buy a 10w oil these days unless I was looking for something specific in the oil and I wasn't using its numbering scheme to determine my purchase, just the actual ingredients and composition of the oil.
for instance, I'd probably use 10w-30 HM Mobil 1 over 5w-30 Mobil 1..... the ingredients inside the bottle are different, not just the way it flows in this case. When I do oil changes on other people's cars I usually use 0w-30 AFE Mobil 1 though if the car is spec'd for 30wt oils.......