A 4-stroke engine keeps its oil in a crankcase, separate from the fuel. That oil has to be the right type, at the right level, and changed before it wears out. The steps below are general. Your owner’s manual lists the oil type and capacity, the filter and plug part numbers, and the service intervals for your engine, and it always comes first.
Checking the oil
- Park level, engine off. A tilted engine gives a false dipstick reading. Many manuals say to check cold, or a few minutes after shutdown so oil drains back.
- Use the dipstick the way the manual describes. Some engines are read with the cap screwed in, others with it resting on the threads. The two methods give different readings.
- Add oil in small amounts. Small crankcases hold little oil, so a few ounces can be the difference between low and overfilled. Overfilling can cause smoking, oil leaks and a wet air filter.
- Check before each use if the manual asks for it. Small air-cooled engines can use some oil between changes, especially under heavy load.
Changing the oil
- Follow the hour-based interval in the manual. Many manuals call for an early first change after break-in, then a regular schedule. Dusty or heavy work may call for the severe-service interval.
- Run the engine briefly first so the oil flows and carries contaminants out, then shut it off and let hot parts cool enough to work safely.
- Drain the way your engine is built: through a drain plug, an oil drain valve, or by tipping the engine as the manual allows. Disconnect the spark plug wire first.
- Replace the oil filter if the engine has one, and refill to the full mark with the viscosity the manual lists.
- Recycle used oil at a collection center. Keep track of the date and hours with the oil change interval tracker.
Air filter
Small engines breathe a lot of dust. Paper elements are generally replaced, not washed. Foam elements and pre-cleaners can often be washed, dried and, if the manual says so, lightly oiled. Never run the engine without its filter. A clogged filter makes the engine run rich, lose power and foul the plug.
Spark plug
Pull the plug at the interval in the manual. Look for heavy carbon, oil fouling or a worn electrode, and replace it with the plug the manual specifies, gapped to spec. Thread it in by hand first so it doesn’t cross-thread, then tighten as directed.
Cooling, fuel and storage
- Keep the cooling fins and shroud clear of grass and debris. Air-cooled engines depend on airflow.
- Use fresh fuel that the manual allows. See storing ethanol-blended gasoline.
- Before long storage, handle fuel, oil and the battery as the manual directs. Equipment-specific steps are in the lawn mower, generator and snowblower guides.
Frequently asked questions
How often should I change the oil in a small engine?
Use the hour-based interval in your owner’s manual. Many manuals also call for an early first change on a new engine and a shorter interval in dusty or heavy-duty use.
Which viscosity does my small engine need?
The one your owner’s manual specifies, which may depend on outdoor temperature. You can also look up your equipment in AMSOIL’s official lookup guide.
Why is my small engine smoking after an oil change?
A common cause is overfilling, or oil reaching the air filter after the engine was tipped the wrong way. Recheck the level on level ground and follow the manual’s tipping direction.
Can I wash a paper air filter?
Generally no. Paper elements are replaced. Foam elements and pre-cleaners can often be washed. Follow your manual.
AMSOIL 100% Synthetic Small-Engine Oil viscosities
Choose the viscosity your owner’s manual specifies, or look up your equipment in AMSOIL’s official lookup guide. AMSOIL offers its 100% Synthetic Small-Engine Oil in these four viscosities:
- AMSOIL 10W-30 100% Synthetic Small-Engine Oil (ASEQT-EA). AMSOIL says: “Tough formulation protects against wear, heat and carbon deposits.” and “Service life up to 200 hours.”
- AMSOIL 5W-30 100% Synthetic Small-Engine Oil (AESQT-EA). AMSOIL says: “Shear-stable, high-film-strength formulation fortified with anti-wear additives.” and lists “Rust-inhibited” among its highlights.
- AMSOIL 10W-40 100% Synthetic Small-Engine Oil (ASFQT-EA). AMSOIL says: “Prevents ring and valve sticking while helping eliminate carbon deposits.” and “Helps extend engine life.”
- AMSOIL 15W-50 100% Synthetic Small-Engine Oil (SEFQT-EA). AMSOIL says: “Heat-resistant synthetic base oils provide low volatility, excellent viscosity stability and strong oxidation resistance.”
Product wording above is quoted or summarized from amsoil.com. Read each product’s label and data sheet for directions. For what the numbers in a viscosity grade mean, see motor oil viscosity explained.