Back when I was younger
motor oils came graded MS/DG (motor severe/diesel general) for general
automotive use and for light-duty diesel engines. We used a diesel-grade oil in or Cat D4 farm tractor,
but bought the stuff in 55-gallon drums. So all of our cars got the same stuff. The diesel grades have
Today's oils are different. They have specialized additives for specific engine types, so you see a bit
more "pickyness" about oil types and grades. But for light-duty applications such as small gensets,
you're not looking at a 1,000,000-mile engine that can expect to be running for 20,000 hours before
first overhaul like a DD S-50 or S-60, so oil is somewhat less critical, though it still needs to be good
I'm a "Valvoline" guy. Won't use anything else -- especially Pennsylvania oils like Penzoil and
Quaker State, due to high paraffin content. Penzoil really deposits an unbelievable amount of
gunk all over the insides of engines where it is used. I pulled the pan off of a Cadillac 425 engine
after 100,000 miles following a custom remanufacture (I did the assembly, a man I know and
trust did all of the meticulous machine work and it ran like a fine Swiss watch). The inside of
that engine was unbelievable! You could have wiped it clean with a paper towel. That's what
100,000 miles with Valvoline gets you. Before the reman, the block sat in the caustic tank for
3 days to get rid of the sludge and gunk from the old Penzoil from previous years.
I'm told that Castrol is a good oil brand, and I suspect that Texaco and others are OK too.
My physics professor from the 1960s was a Standard Oil bulk distributor in an earlier life, and
he was quite vivid in explaining the problems encountered with Pennsylvania-based oils, especially
in the high mountain valley of Southern Colorado where I grew up where the winter temperatures
can get to -40 (F or C -- doesn't matter; that's where the two scales cross over each other) and
frozen gas lines are a major concern (I was stranded close to a half-mile from the nearest telephone
one night in December 1961 due to a frozen gas line in my dad's car on my way to take a night-time
final exam at college in Alamosa. It was 40 below).
Alamosa is frequently the coldest town in the US in the middle of winter.