Outboard engine lubrication: two-stroke and four-stroke
An outboard engine works in conditions very different from a car engine. It runs for hours at a constantly high load, it is exposed to salt water and humidity, and it often sits unused for weeks or months. Correct lubrication is one of the simplest ways to protect your boat's engine.
Two-stroke or four-stroke?
The first step is to know which engine you have, because the two types are lubricated in completely different ways.
- In a two-stroke (2T) engine the oil is mixed with the petrol, either in the tank or through an automatic oil injection system. The oil lubricates the engine and is then burned together with the fuel.
- In a four-stroke (4T) engine the oil sits in the crankcase, as in a car, circulates continuously and is changed at regular intervals.
The oils of the two types are not interchangeable. A 4T oil is not meant to be mixed with fuel, and a 2T oil is not meant for the crankcase of a four-stroke.
Two-stroke outboards and NMMA TC-W3
For water-cooled two-stroke outboard engines the key specification is NMMA TC-W3, set by the US National Marine Manufacturers Association (NMMA). An oil meeting this specification is designed for the operating conditions of water-cooled two-stroke engines and for clean combustion in the mixture.
PARNAS MAREA 2 is a lubricant of special composition for modern two-stroke outboard engines and meets NMMA TC-W3.
A few practical tips:
- Keep to the mixing ratio set by the engine manufacturer. Not less oil, and not "a little extra to be safe".
- Mix in a clean container and shake well before refuelling.
- On engines with automatic oil injection, check the oil tank level before every trip.
- Do not use oil meant for air-cooled two-stroke engines (motorcycles, garden machinery) in an outboard, unless the manufacturer explicitly allows it.
Four-stroke outboards
Four-stroke outboards use crankcase oil with the viscosity and specification set by the manufacturer. Conditions are, however, more demanding than in a car: constantly high revs for long periods, humidity and long periods of inactivity.
MAREA 4 SAE 10W-40 is a semi-synthetic lubricant for four-stroke outboard engines, with specification API SJ. Check that the viscosity and specification match those required by your engine manual.
Tips for four-strokes:
- Check the oil level before every trip, with the engine upright as the manual specifies.
- Change oil and filter according to the operating hours or time interval set by the manufacturer, whichever comes first.
- If the oil looks milky, water may have entered. Have it checked by a specialist before using the engine again.
Do not forget the gearcase
On both engine types the lower unit, the gearcase, has its own gear lubricant, separate from the engine oil. Use the lubricant specified by the manufacturer and check its condition at scheduled services. If the lubricant is cloudy or milky when drained, water is probably getting in and the seals need checking. For gear lubricants see our gear oils category and ask us to confirm suitability for your engine.
Before the winter lay-up
The end of the season is the best time for maintenance:
- On four-stroke engines, many manufacturers recommend an oil and filter change before storage, so the engine does not spend the winter months with used oil.
- Flush the cooling circuit with fresh water following the manufacturer's instructions.
- Check and, if needed, change the gearcase lubricant.
- Lubricate the points listed in the manual (steering and tilt mechanisms) with the grease specified.
- Follow the manufacturer's instructions for the fuel left in the system during storage.
Need help?
Tell us the make, model and type of your outboard (2T or 4T) and we will suggest the right lubricant from our marine lubricants. Contact us or see all our products.