Briggs' chart shows SAE30 from 4C to the top of the chart at 49C. However I think the use of SAE40 in really hot conditions would probably reduce oil consumption without causing problems. The issue Briggs seem to be concerned about, is difficulty spinning the engine fast enough to start it, in cold weather. You can't rely on the operator to change oil seasonally, so they would be in danger of getting customer complaints in winter if they authorised SAE40.
Many years ago (until the very early 1980s) Holden used to fill their 6 cylinder engines with DTE Light oil in the plant, as a running-in oil, and instructed the customer to have it changed as part of the initial 1,000 mile service. They were forced to abandon the practice because of the number of cars that were first serviced at 10,000 miles, and still had the DTE Light in them.
We all have to recognise that the customer we can get is the customer we want, and we'd better make it easy for him or her to get good results.
