A 10w-30 oil is a 10 grade oil. It's not even close to a 30w in grade. Using water cooled car oil in an air cooled engine, needs to be revisited.
Please let me know when it pops up on Craig's List in the free mower section.
slomo
In the near future no straight 30 oil will exist. Lube engineers have decided that there is no need to keep the straight weight oils as there is so little use for them. I use 0W-30 Mobil 1 in my X304. Kawasaki and JD recommend 10W-30 for their air cooled engines.
Most of us "know" that 90% of engine damage comes not when running hard flat out, but at the first 30-60 sec. after start-up when the oil is still thick and not flowing well. What most people don't know, is that even 0W oil is too thick at 100*F to properly flow and lube at startup. Let me repeat that, 0W oil is too THICK at 100 deg. F. So what do we do? We spec our oil for that 1 day in late July when we just got to mow the yard and it's 104*F outside. If 10W-30 is good, well 15W-40 must be better. If we're hot and miserable, then our engines must be hot also.
I run 0W-30 Mobil 1 in all of my engines. I accept that they may use more oil than straight 30HD, but I check my oil everytime I start my equipment anyway, and have not yet needed to add any oil between my annual changes, yet. I've been using 0W-30 for about 5 years now. I don't really know if this is better, and barring catastrophic failure will likely never know, but I think the engines start easier, and I feel better about it.
steve