Changing the Oil and Filter in a Mercury FourStroke Outboard
You don’t have to be a master mechanic to change the crankcase oil in an outboard.
In fact, with a few basic tools and a willingness to learn, changing your outboard oil can be done in a matter of minutes. Simply follow the steps in this helpful how-to video from the folks at Wired2Fish.com
In this video, the oil is being changed on a Mercury® 4.6L V8 300hp FourStroke outboard, and these same basic steps apply to most Mercury FourStroke, Pro XS® and Verado® outboards built on the 3.4L V6 or 4.6L V8 platforms.
To change the oil in the Mercury 300hp FourStroke outboard you’ll need the following:
Oil filter wrench
5/8-inch deep-well socket
7/16-inch internal diameter clear plastic drain tube (2 pieces, 3-4 feet long is ideal)
Most outboards have an oil change interval of 100 hours of operation or once per year, whichever comes first, but consult your owner’s manual to see just what is recommended for your make and model. Many boaters prefer to do their annual oil change during winterization to ensure that there won’t be any moisture in the crankcase while the engine is stored for the winter.
Here is the basic procedure:
Oil changes are best performed when the outboard engine is warm. With a warm engine, oil drains faster and more thoroughly. Therefore, performing the oil change right after coming off the water (or after running it on the motor flushing “earmuffs”) is ideal. In the event you aren’t able to run your engine ahead of time, you still should change it at the recommended intervals. So, don’t put off an oil change just because you’re not able to run the engine before doing so.
Remove the cowl, then trim the engine all the way up and leave it in that position for a few minutes. This will help drain all the oil from the upper end of the engine into the sump. Then lower the engine back down until the propeller shaft is parallel to the ground.
The oil drain on the 6L FourStroke outboard is located on the starboard (right-hand) side of the outboard, not far above the lower unit. Using your ratchet and deep-well socket, loosen the oil drain about a half turn or until it can be turned by hand. Important: This is not a traditional oil drain plug that you take all the way out, so don’t be tempted to remove it.
Slide one end of the plastic drain tube over the end of the oil drain, then continue turning the oil drain (and tube) counterclockwise until you see the engine oil start to appear in the tube. Turn it enough that the oil can flow freely, then let it continue to drain into your waste oil pan.
With the oil draining, you can now change the oil filter, which is located near the top of the powerhead on the port (left) side of the outboard. To change the filter, follow these simple steps:
Remove the yellow rubber plug located just below the oil filter. Next, fit a drain line over the fitting where the plug was located. Be sure the other end of the drain tube is appropriately positioned in a small container suitable for a few ounces of used oil.
Using your filter wrench, slowly loosen the oil filter by turning it counterclockwise. Pause for a minute or so after a few turns to allow any oil that was trapped in the filter to drain through the tube.
Continue to loosen the filter until it’s free. Then quickly turn it open-side up and dispose of it properly.
Prepare your new Quicksilver oil filter by putting a small amount of new motor oil on a clean finger, then use it to pre-lube the filter’s gasket.
Carefully thread the new filter onto the outboard, tightening as much as you can by hand. Finish by turning it an additional half to three-quarters of a turn with your filter wrench. Do not overtighten as this can make the filter extremely hard to remove during your next oil change and may in fact damage the new filter.
Remove the drain hose and replace the yellow rubber plug, taking care to wipe up all spills and drips with a rag or paper towel.
Pro Tip: Write the date and engine hours on the end of the filter with a permanent marker as a visual reminder and record of the oil change.
The engine oil should be fully drained at this point, so go back to the starboard side of the engine. With a rag at the ready, remove the drain tube from the oil drain and quickly close it up by hand by turning it clockwise. Finish snugging it up with your ratchet and deep-well socket, then wipe down the oil drain area with your rag.
Finally, it’s time to pour in the new oil by removing the yellow plug at the top of the engine. You’ll probably need a step stool, or just climb into the boat, to comfortably pour the oil into the crankcase without spilling. If you bought your oil in quart containers, you can just put your funnel into the oil fill hole and pour in 7 quarts. If you purchased the gallon containers of oil, pour in the full contents of the first container, but stop just before you’re halfway through the second gallon. This will help to prevent overfilling.
Next, pull out the dipstick that is located right next to the oil fill hole. Wipe it off with a rag, put it back in, then pull it out once again to get an accurate reading. The dipstick will have a series of yellow beads attached to the bottom of it; when full, the oil level should be touching the uppermost bead. If the level is below the top bead at this point, add a few more ounces of oil, check the level again, and repeat until the oil is up to the top bead of the dipstick. Once the level is where you want it, remove the funnel and replace the oil fill cap.
If you are able, run the engine for a few minutes with the cowl off, making sure there are no leaks. Once you turn it off, give the oil 10-15 minutes to settle back down and check the level again. Top off if necessary and then replace the cowl.
With that, your oil and filter change is complete! Now, it’s also a good idea to check your gearcase lube and perform other basic maintenance in conjunction with your oil change.