slant 6 oil weight

SH rated motor oil is still available from Kohler. It is oil used in their small air cooled engines. The recommended oil and filter change is 100 hours. 100 hours x 60 mph = 6000 miles.

Decades ago I used Amoco Superblend 10w30 in the winter. Changed to their straight 30 weight in the summer. Gained about 10 psi at hot idle. Even so, when draining the oil after a long drive in the summer [30 wt], it came out like a cow pissing on a flat rock.

This does not apply to newer engines. My 2.4 na calls for 5w30. That's all it gets. And after 100,000 miles, it sounds like a new engine.