Use 10W-30 for most weather, switch to SAE 30 for steady heat above 40°F (4°C), use 5W-30 for cold starts near or below freezing, and follow your engine manual.
Quick Answer: Pick An Oil Weight That Matches The Day
Mower engines are air-cooled and run hot under load. That heat thins oil, so the right viscosity keeps a protective film on bearings, rings, and the cam. A simple way to decide: match the weight to the temperature you actually mow in, then confirm the brand’s chart. As a rule of thumb, multi-grade oils like 10W-30 or 5W-30 handle swings from chilly mornings to warm afternoons. A straight SAE 30 works well once spring warms up and stays warm. If you mow in wide swings or push a heavy deck, a quality full synthetic 5W-30 or 10W-30 gives steady viscosity and strong start-up flow. When in doubt, check the maker’s table and select the weight that covers your usual range.
Brand & Temperature Cheatsheet
The table below maps common small-engine brands to practical picks. Always verify in your model’s manual or the brand’s oil page before you fill.
| Engine Brand | Typical Temp Window | Go-To Oil Weight |
|---|---|---|
| Briggs & Stratton | Below 40°F to hot summer | 5W-30 synthetic for broad range; 10W-30 for mixed weather; SAE 30 once days stay >40°F (see Briggs oil guide) |
| Kawasaki | Mixed climates; heavy zero-turn work | 10W-40 for most use; 20W-50 to curb consumption in high heat (see Kawasaki FAQ) |
| Honda GX/GXV | Cool mornings to warm afternoons | 10W-30 for general use; 5W-30 for cold starts (see Honda manual) |
| Kohler | Seasonal swings | 10W-30 or 10W-40 per chart; heavier grades in sustained heat as advised in model docs |
How Oil “Weight” Works
Oil “weight” is simply a viscosity grade set by the SAE J300 standard. A grade with a “W” such as 10W-30 means the oil meets a winter flow test and also a hot-running test at operating temperature. The first number speaks to cold cranking behavior. The second number describes thickness when the engine is hot. That is why 10W-30 pours like a thinner oil a