How to Change Mercury 20HP Outboard Oil

Changing the oil on a Mercury 20 outboard is recommended after every 100 hours of service. Grab a couple of tools, some oil and the filter, and you can knock it out in minutes.

Watch the video above and follow the steps below to change the oil in a Mercury 20 outboard.

Tools and Supplies - Mercury 20HP Outboard Oil Change

  • 16mm socket
  • 3/8th ratchet
  • 65mm oil filter wrench

Mercury 10W-30 4-stroke oil

Mercury 20 oil filter


Mercury 20 Outboard Oil Change

Step 1. Lift the motor by pulling up the lower unit from the bottom to tilt the motor up, while pulling down on the lever on the right hand (as viewed from the rear) side of the motor. This lever will prop the motor in place. 

Mercury 20HP outboard oil change

Mercury 20 outboard oil change

Step 2. Get a drain pan ready, and remove the drain bolt to start draining the oil.  

Mercury 20 HP outboard oil change

Step 3. Replace the drain bolt and return the motor to its vertical position. Leave it there for a few minutes to allow the last of the old oil to get to the foot of the motor. Lift the motor again, remove the drain bolt, and drain the last of the oil.  

Mercury 20 outboard oil drain

Step 4. Replace the drain bolt after all the oil is drained. Use a torque wrench to tighten the bolt to 17 foot-pounds.  

Mercury 20HP outboard engine oil change

Step 5. Release the lever again and lower the motor. Next, remove the cowl by lifting up on the latch at the back of the motor and then lifting the cowl off. 

Mercury outboard motor oil change

Step 6. Find the oil filter, located on the left side (when viewed from the rear) of the motor. Stuff a rag underneath the oil filter to keep oil from running out of it and down into the engine cover when you remove it.  

Merc 20 outboard motor oil change

Step 7. Use your 65mm oil filter wrench to remove the oil filter. 

NOTE: There's a gasket on the oil filter. Make sure it comes off with the filter and isn't stuck on the engine. Otherwise when the new filter is installed, this will cause it to leak.  

Merc 20HP outboard engine oil change

Mercury 20HP outboard oil filter change

Step 8. Use your finger to apply a thin coat of oil on the gasket on the back of the new oil filter

NOTE: This step makes it easier to remove the filter when it's time to replace it. 

Mercury 20 outboard oil change

Step 9. Replace the oil filter. Thread it on by hand until the gasket contacts the engine. Then, use your 65mm oil filter wrench to tighten it another ¾ turn. 

Mercury 20 outboard oil filter install

Step 10. Remove the oil fill cap at the rear of the engine, and fill the engine with motor oil

PRO TIP: The Mercury 20HP outboard engine takes 1.1 quarts of oil, so add 1 quart, replace the cap, and run the engine for a couple of minutes. When you run it, be sure to have water circulating through the engine as you would when you flush the engine out after use. 

Mercury 20HP outboard engine oil refill

Mercury 20HP outboard motor oil refill

Step 11. Remove the dipstick on the right side of the engine, wipe it off, and push it all the way in until it bottoms out. Then, remove the dipstick again and check the oil level. 

NOTE: With 1 quart, our oil level was low. The three holes in the dipstick represent low, medium, and high. Mercury specifies the oil level should be around the middle hole.

20HP outboard motor oil change Mercury

Merc 20 outboard oil level dipstick

Step 12. Add a little oil if the level is low and check it again. 

NOTE: Since we already added 1 quart, this should require about .1 quarts to get the level right in the middle range.

Step 13. Replace the dipstick once the oil level is set properly, then put the cowling back on and you're done.




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