I personally don't believe there is anything inherently wrong with a group III oil, except for the fact that it may be not quite as good as a group IV or group V, costs less to produce than the IV and V and the companies charge full price for it. Looking at the Shell 5w-40 for $3.25 quart at walmart (when bought by the gallon) and the Group III looks like a good deal. Also, many people don't realize it, but BMW sells the 5w-30 group III Castrol (which does not appear to be the 5w-30 syntect given its nearly 40 weight CST when new) for less than $4.00 quart. The only problem with the BMW oil appears to be BMW's insistance on pushing it to 15,000 miles when it is more realistically a 10,000 mile oil (I guess that extra $1 quart for the Mobil 1 buys you the extra 5,000 miles)
While I am not a fan of the Castrol 5w-50, I believe it has turned in some pretty decent UOA's. For me, I am sticking with Mobil 1 or Redline. For my father-in-law's 91 Mercedes (who is bad about maintence), I am putting in the Shell Group III because I feel comfortable it will go 7500-10,000 miles in better shape than mineral, while not breaking the bank.
Cary
While I am not a fan of the Castrol 5w-50, I believe it has turned in some pretty decent UOA's. For me, I am sticking with Mobil 1 or Redline. For my father-in-law's 91 Mercedes (who is bad about maintence), I am putting in the Shell Group III because I feel comfortable it will go 7500-10,000 miles in better shape than mineral, while not breaking the bank.
Cary