Personally, I don't worry about motor oil as far as quality anymore. The days of Parafine based motor oil are gone due to EPA regulations. And with added detergents, MOST motor oil is going to be clean. The other fact I'm aware of, is Motor Oil never ever wears out. NEVER EVER. It will always have lubricating properties. The reason motor oil needs changed is because it gets diluted. As said, the trick is a good filter to catch most of the contaminents, and keep your motor clean in the first place. Starting with a dirty motor that was neglected, needs more oil changes and Sea Foam crankcase treatments. I know some of you are going to fall out of your chair when I say this, but my 460 Box Van has over 180,000 miles on it, and I change the oil every 10,000 miles. I use full synthetic, and a Mobil 1 Filter. And when I do change it, it's usually still a dark golden color. Not a light gold when it first went in, but nowhere near black at all. I do also do SeaFoam crankcase treatments about every 3rd or 4th oil change. I'll put a half bottle of Sea Foam in the crankcase, and leave it there for the last 200-300 miles before changing the oil. Keep your crankcase clean, use a good filter and you'll never have a problem with black oil until your rings and valve seals and guides and letting alot of burnt combustion get into the crankcase. My squares, I usually run conventional oil and a good filter, like Motorcraft or Puroloater Pure One, which are the same filter by they way, just the Motorcraft filter is about $4-$5 compared to $8-$10 for the Purolater. I also do the SeaFoam treatments every 3 or 4 changes and I still get gold oil out of them too. It's all a matter of keeping the motor clean, not so much what brand of oil these days. I'll even use Penzoil these days, but I damn sure wouldn't 10-15 years ago. Arnold Palmer is a lying sumbish saying that tractor did what it did. Penzoil and parafined based oils were the worst back in the day. Parafine is like pouring candle wax in your motor. JMO, and I'll stick with what works for me as long as I keep getting golden oil between changes, even if it is dark gold.