How to Change Mercury 115HP Oil & Filter

Changing the oil and oil filter on a Mercury 115HP EFI outboard is a quick do-it-yourself type of job. An OEM Mercury oil filter and Mercury engine oil are recommended for this job. 

Mercury recommends changing the oil at least once after every 100 hours of use, and doing it yourself saves the trouble of having to pay a mechanic repeatedly to do it for you. Watch the video above and follow the steps below to change the oil and filter in a Mercury 115 outboard.

Tools and Supplies - Mercury 115 Outboard Oil Change

• 18mm socket
• 3/8" ratchet
• Pick tool

• 65mm oil filter wrench
• Mercury oil change kit
• Mercury oil filter

The simplest and cheapest method of changing a Mercury 115 outboard's oil filter and oil is to purchase a Mercury oil change kit. The kit includes a Mercury oil filter, 5 quarts of oil and a replacement crush washer. You can also purchase the parts separately. 

PRO TIP: Run your outboard for a minute or two before changing the engine oil. This warms the old oil, and makes it flow and drain out better.

Mercury 115HP EFI Outboard Oil and Filter Change

Step 1. Remove the top engine cowling, raise the outboard fully up to the trailer position and tilt the engine so the drain plug (on the left side of the motor) is leaning toward the ground.

Step 2. Remove the 18mm oil drain bolt, and allow the engine oil to drain out into a drain pan.

NOTE: Check to see whether the old crush washer has stuck to the side of the engine block around the drain hole. If it has, remove it and discard it. Don't reuse old crush washers because they no longer provide a reliable seal.

Step 3. Put a new crush washer on the oil drain bolt and reinstall the bolt into the drain hole. Tighten the drain bolt until it bottoms out on the engine block, and then give it an additional quarter of a turn to compress the crush washer and get a good seal. Don't overtighten the drain bolt.

Step 4. Lower the outboard back down to the running position, and place some rags or shop towels beneath the oil filter (on the right side of the outboard) to catch any oil that may spill out when you remove it.

Step 5. Remove the old oil filter with a 65mm oil filter wrench. If the filter's gasket sticks to the engine block, remove it with a pick tool, being careful not to scratch the surface of the engine.

Step 6. Smear a thin coat of oil onto the new oil filter's rubber gasket and install the new filter, tightening it by hand until you feel it make contact with the engine block. Then, tighten it down with a wrench by ¾ of a turn.

Step 7. Remove the oil filler cap (at the upper rear of the outboard) and fill the engine with the type and quantity of oil specified in your Mercury owner's manual. Replace the filler cap.

Step 8. Run the motor for a couple of minutes to distribute the new oil throughout the motor, then let it sit for a minute. Next, check the oil level using the dipstick (just below the oil filter), and top off the oil level if necessary. 

Step 9. Check the oil filter and oil drain bolt for any leaks and tighten them if necessary. Replace the top engine cowling and you're done.