I was reading my chilton book and owners manual the other day and it says to only use oil that has is "energy conserving II" and with a grade of SG or SL can be used. I have been using Valvoline but it only says I think "SM" on the label. Whats the deal with these letters and what do they mean. It says do not use anything that does not have these letters. I was using 10W-30 but switched to 5W-30 last night. I think thats what I am supposed to be using anyways. Any comments on this? Any help would be appreciated.