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How To Change The Oil In A 4-Stroke Outboard Engine

Oil is the lifeblood of your outboard. Follow these tips when it's time for a transfusion, or at least an oil change.

So, you're basically a DIY sort of boater, and your new four-stroke outboard is not so new anymore. It's past the warranty period, and you're ready to do some maintenance on your own in the hopes of saving some cash. Changing the oil is one of the best things you can do to prolong the life of your outboard, and it's an uncomplicated job that's well within the realms of an enthusiastic owner.

That being said, if your engine is still under warranty, and you're not that mechanically inclined, you might want to consider not doing your own oil changes and leave it up to the dealer, especially if additional work is required. Yes, it will cost more than doing it yourself. But there are some good reasons, especially during the factory warranty period, to simply let the dealer do this work:

  • If anything goes wrong with the engine internally, and it has anything to do with lubrication or the lack thereof, you're not even in the equation. All the responsibility lies with the dealer if the engine is still under warranty.
  • When it comes time to resell, having all dealer records of each service goes a long way toward a successful sale, and a higher price.

If you're so inclined, however, changing your own oil is not all that complicated, plus there are some benefits outside saving money. You'll learn a little more about your engine and get a closer feel for what makes it tick. Best of all, you get the satisfaction of doing it yourself.

How To Change The Oil Step-by-Step

Technical Support

Degree Of Difficulty: Easy to Moderate

Tools and Materials:

  • Remote oil change pump (if needed)
  • Drain pan
  • Funnel
  • Wrenches
  • Screwdriver
  • Grease gun with Zerk fitting
  • Marine four-stroke oil
  • Filter(s)
  • Waste oil container
  • Trash bags
  • Gallon-sized resealable bag
  • Marine waterproof grease
  • Rags

Time: 1 hour.

Cost: Around $50 in materials (depending on size of engine.

Trimming down a Suzuki-115 engine

1. I start by tilting our subject Suzuki 115 four-stroke down to the running position in order to drain all oil effectively. Follow the manufacturer's recommendations for your specific outboard. Warm up the engine (not shown) to ensure that the crankcase oil gets warm and flows easy for more complete draining. (If the boat is not in the water, you'll need to use muffs.)

Removing lower cowl

2. In this engine, I need to remove the lower cowls in order to access the drain screw and oil filter.

Removing or installing oil drain screw

3. Remove the drain screw. This one on the starboard side of the exhaust housing is fairly easy to access. Other motors have a drain plug in the aft end of the lower unit.

Draining engine oil

4. Be ready with a drain pan to catch the oil. In addition, you may want to lay some type of barrier on the ground to protect against spillage. NOTE: Some newer engine models are designed to use only an oil extraction pump (not shown). On these engines, the pump lift tube should reach all the way to the bottom of the crankcase to effectively pull out all the old oil and any debris inside. If your outboard doesn't have this feature, it's preferable to use the drain-plug method in order to ensure complete drainage.

Removing old oil filter

5. Remove the old filter (you may need an oil filter wrench if it was tightened excessively) and reinstall the drain plug if you removed one.

Oiling O-ring on new oil filter

6. Before installing the new filter, lubricate the O-ring seal with fresh oil.

Installing new air filter

7. Install and hand tighten the new filter.

Adding engine oil

8. Refill the crankcase with fresh marine four-stroke outboard oil, preferably the manufacturer's brand, using the amount required by the manufacturer. Carefully check the level, making sure that it reaches the full mark on the dipstick. Replace the dipstick, then start the engine and let it idle for 15 to 30 seconds — nothing above idle speed! The idea here is simply to distribute the new oil throughout the crankcase and cylinder head, and to fill the filter.


Use a gallon-size resealable bag turned inside out to grab the used oil filter as you take it off, then close it up to eliminate drips.
Oil dipstick

Photo: Gettyimages/Vladimir Mucibabic

9. Stop the engine and check the oil level, adding extra if it's below maximum, until it reaches the proper level on the dipstick. Start the engine again, let it idle some, rev it slightly, and shut off again. Check the oil level one last time. After running for several minutes, check the new filter to be sure it's not leaking around the seal.

Greasing swivel bracket fitting

10. While you're at it, grease all fittings on the outboard with marine waterproof grease. You'll need a grease gun with a Zerk fitting. Check the service manual for all Zerk fitting locations.

10 Tips For Success

  • Get a factory service manual for your specific year, make, and model engine. Most sell for less than $50, and it's money well spent. Cheaper aftermarket manuals typically address multiple engines across multiple years, the descriptions and illustrations are not as clear, and some have even been known to publish incorrect information.
  • Change the filter at the same time you change the oil. Like your car, fresh oil requires a clean filter to be effective in lubricating your outboard.
  • Ask your dealer to recommend the correct oil and filter. Typically, the factory oil and filter is the way to go. A few bucks saved on aftermarket oil and filters may cost dearly if you pick the wrong stuff, and it can void your warranty.
  • Read your manual, and confer with your dealer, on the best way to extract the old oil from your engine. Some engines have a drain plug; others must have the oil sucked outward through the dipstick tube. For that, you'll need a special oil extraction pump, which you can find at West Marine (
  • If you're attempting to change the oil when your boat's in the water, be aware of the potential consequences of spillage, which could land you a hefty fine.
  • Properly dispose of the waste oil and filter, but not before you rub a little of the recently removed oil between your fingers. If the oil feels at all gritty or has a burnt smell to it, it could be an indicator of problems. Have the shop look at it.
  • Carefully document each service: date/time, hours (if possible), type of oil and filter used, disposal method, old oil condition, and any other pertinent conditions.
  • Ask the boatyard if you can change the oil on their property — not all yards will allow you to do your own work — and ask if they can recycle the oil for you.
  • Don't use automotive oils and filters. Marine oils are specially formulated for harsh and wet conditions, prolonged periods of inactivity, and much higher exposure to potential rust and corrosion.
  • Follow factory procedures and advice to the letter.

Environmental Matters

Disposing of used oil can be a messy problem because it's considered hazardous waste. Petroleum products are toxic to fish, plants, and animals, and if they're not handled properly they can contaminate soil and waterways, resulting in environmental damage, costly cleanup, and possibly even federal fines. Luckily, used engine oil can be easily and safely recycled. Ask your marina if it offers collection of used oil for recycling, and if it does, be sure to follow its guidelines for handling it. If this isn't an option, check with your local automobile repair shop or auto parts store, or visit to do a search near your location.

Did you know that your oil filter can be recycled, too? Oil filters are made of steel, which is America's number-one recycled material. If all the filters sold annually in the U.S. were recycled, enough steel would be recovered to produce 160,000 new cars! You can also search for local recycling drop-off locations at the Earth911 website.

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John Tiger

Contributor, BoatUS Magazine

John Tiger is a freelance boating writer and frequent contributor to many magazines.