Here is the Briggs oil recommendation chart. It supersedes ALL previous oil recommendations. So if your oil recommendation in your manual does not look like this, then it is not the currently recommended oil suggestion. I do find it curious that they recommend 30 weights, and now a 50 weight oil, but completely bypass the very excellent SAE40 and 15W40 oils. CLEARLY a 40 weight oil is fine in these engines, in hot temps, if a 50 weight oil is fine and recommended by the manufacturer.
* Below 40°F (4°C) the use of SAE 30 will result in hard starting.
** Above 80°F (27°C) the use of 10W30 may cause increased oil consumption. Check oil level more frequently.
This little blurb below from their website, wasn't there before. This is NEW information, as of this year. They got tired of warranty replacing engines early in Texas, Arizona, and Florida on commercially used power equipment, stationary pumps, and generators.:
"Outdoor temperatures determine the proper oil viscosity for the engine. Use the chart to select the best viscosity for the outdoor temperature range expected. Engines on most outdoor power equipment operate well with 5W30 Synthetic oil. For equipment operated in hot temperatures, Vanguard 15W50 Synthetic oil provides the best protection."
According to Briggs website, this is what they have to say about their Vanguard synthetic 15W50:
"Vanguard 15W-50 100% Full Synthetic engine oil was designed for demanding commercial engine applications.
It is ideal for prolonged use work applications that require maximum engine protection and performance.
100% Full Synthetic
Reduced Oil Consumption
Longer Life
Zinc anti-wear additive
Operating temperature range 20° to 130°
Designed for commercial engine applications
Warranty-approved
Designed for use in commercial applications such as zero-turn mowers, pressure washers, ride-on mowers, etc., and can save on costly repairs while maintaining warranty coverage. "