The main difference in a 4 stroke vs 2 stroke outboard is how the engine completes its power cycle and how it is lubricated. A two-stroke fires on every turn of the crankshaft and burns oil mixed into its fuel, while a four-stroke fires on every second turn and keeps its oil in a separate crankcase, much like a car engine. Every outboard we sell is a four-stroke.
How a two-stroke outboard works
A two-stroke completes intake, compression, power and exhaust in just two strokes of the piston, so it makes a power stroke on every crankshaft revolution. It has no camshaft or valves; the moving piston opens and closes ports in the cylinder wall. Lubricating oil is either premixed with the gasoline by the owner or metered in by an oil-injection system, and that oil is burned along with the fuel.
The simple layout, with fewer moving parts, is why two-strokes have a reputation for being light and compact for the power they make.
How a four-stroke outboard works
A four-stroke gives intake, compression, power and exhaust a stroke each, so it fires once every two crankshaft revolutions. Valves driven by a camshaft control the flow of air, fuel and exhaust. Engine oil is held in a sump in the crankcase rather than burned with the fuel, so you fill the tank with gasoline only and change the oil at the intervals in the owner’s manual.
4 stroke vs 2 stroke outboard at a glance
| Factor | Two-stroke | Four-stroke |
|---|---|---|
| Power stroke | Every crankshaft revolution | Every second revolution |
| Lubrication | Oil mixed with fuel or injected, then burned | Separate oil sump; periodic oil changes |
| Fuel | Gasoline plus two-stroke oil | Gasoline only |
| Weight | Generally lighter for the same horsepower | Generally heavier for the same horsepower |
| Sound and idle | Louder, rougher at idle | Quieter, smoother at idle |
| Fuel use | Higher, especially older carbureted designs | Generally lower |
| Moving parts | Fewer, no valvetrain | More, including valves and camshaft |
Is a 4 stroke or 2 stroke outboard better for your boat?
Neither design suits every boater. A two-stroke appeals to owners who want the least weight for the horsepower and simple mechanicals. A four-stroke suits owners who value quiet running, a smooth idle for trolling, lower fuel use and not having to mix oil into their gas. Ask yourself:
- Will you carry the motor? On a portable motor, a few extra pounds matter every time you lift it.
- How much time do you spend at idle or trolling speed? Smooth, quiet low-speed running is where four-strokes are most noticeable.
- What can your transom handle? Check your boat’s capacity plate for its maximum horsepower, and remember a four-stroke can weigh more than a two-stroke of the same rating.
- Who will service it? Four-strokes need oil changes and the scheduled service in the manual; two-strokes need the right oil supply every time you fuel up.
Owning a four-stroke outboard
- Check the oil level before each trip and change it at the interval the manual gives.
- When you lay a portable four-stroke down for transport or storage, use only the side the owner’s manual shows, so oil does not run into parts of the engine where it does not belong.
- Prepare it for the off-season with our guide on how to winterize an outboard motor.
- Match the shaft to your transom height with the outboard shaft length guide.
Four-stroke outboards we carry
We carry Suzuki, Tohatsu and Mercury four-stroke outboards from 2.5 to 30 HP, including several Mercury EFI (electronic fuel injection) models. If you are replacing an older two-stroke, start by matching horsepower and shaft length. Lighter motors for tenders and small boats are in our portable range, a common size for small fishing boats is in 9.9 HP outboards, and every model is listed by power under outboard motors for sale by horsepower.
More guides: who makes Tohatsu outboards? · outboard break-in procedure · outboard won’t idle · outboard engine hours · how to change outboard oil · ethanol in boat fuel · Tohatsu vs Mercury · EFI vs carbureted · outboard motor prices by HP.
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