Originally Posted By: CaspianM
Why such thick oil needed for a small engine? Unnecessary shear stress which creates more friction & rotational drag. Motor oil has gone a long way.
Today the thinnest oil that works is the one to use.
The reason is that these small engines are air cooled, and even then - cooling is minimal. They run hot and especially in hot weather down south, a standard 30-wt will not cut it. Many Katrina survivors that had generators can testify to this, as many of those that ran thinner oils on a continuous-operation basis experienced engine failures. Not all, but many. Summer temps and air-cooled engines can benefit from a 40-wt (or greater), but a robust 30-wt would probably work as well.
For the price, level of protection, and piece of mind, it's hard to beat a good ole HDEO 15w40 (Rotella, Delo, ST, Delvac) in summer temps. In the winter, a standard 30-wt would suffice.