From the manufacturer:
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Different oil types can work best at certain temperatures. Learn which one to choose for your climate.
SAE 30- Warmer temperatures, most common oil for small engines.
SAE 10W-30- Varying temperature range, this grade of oil improves cold weather starting, but may increase oil consumption.
Synthetic SAE 5W-30- Best protection at all temperatures as well as improved starting with less oil consumption.
SAE 5W-30- Very cold temperatures.
Vanguard 15W-50- Varying temperature range. For continuous-use, such as commercial lawn cutting or pressure washing.
When choosing lawn mower oil, use a high quality detergent oil classified as "For Service SF, SG, SH, SJ" or higher. Do not use special additives.
Synthetic oils are an acceptable oil at all temperatures. Use of synthetic oil does not alter required oil change intervals.
Can you use synthetic lawn mower oil? Yes!
Synthetic Lawnmower Oil by Briggs & Stratton
We have modified our engine oil recommendations to state that you may now use a synthetic 5W30 (100074WEB) or 10W30 oil in all temperature ranges. We recommend the use of Briggs & Stratton Synthetic Oil. The use of this high quality detergent oil assures compliance with Briggs & Stratton warranty requirements regarding the use of appropriate oil.
Engine break-in procedures using synthetic oil remain the same. Keep in mind that the use of synthetic oil does not prevent you from performing your regularly scheduled lawn mower maintenance (i.e. check oil, change oil, etc.)
*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.