For extreme conditions, hot and cold especially with air cooled engines we've found that in emergency pumps and generators if you absolutely need the best oil then an ester based synthetic oil is the choice. My daughter is still using my 1980's era Eager 1 Sears mower that has been run on ester based 5w30 oil. My son-in-law changes it based on the amount of gasoline used over the season. I agree that gasoline used is a good measure of the amount of work done by the engine and a good method to time oil changes. I use the same method for all my small engines and I'm thinking of applying it to my cars as well.