How to Change Your Mercruiser Engine Oil

Read your Owners Manual and its Safety Precautions.

In general, you need to change your oil every year or every 100 hours of use, whichever comes first.

Visually inspect your engine and check the oil before starting.

Make sure the prop has been removed and that no people or pets are near the stern drive or prop before starting the motor.

Check for fuel or fuel vapors outside or in a well ventilated area to prevent Carbon Monoxide poisoning to people.

Make sure your engine has a water supply before starting.

Be prepared for spilt oil. Cover your floor and cushions with old towels or blankets.

Start your motor and let it warm up. This will warm up the oil and make it much easier to suck it up and out of your dipstick tube.

Turn the motor Off. After the engine has run long enough to reach operating temperature turn the motor off and let it cool for a few minutes.

Remove the dipstick and thread the oil hand pump onto the end of the dipstick tube. If you are using an electric oil changer bucket hook up the hose to the tube and attach the pumps wires to the battery (red is positive and black is negative).

Suck out your oil into a container. Mer cruiser dipstick tubes are also Oil Withdraw tubes. You can suck all the oil out of the engine through the dipstick tube. This requires the use of either a small hand pump (part 802899A1 Oil Pump which can be purchased online or you can buy a more expensive Oil Changer Pump/Bucket Assembly from a marine supply store (about $160.00 and up).

Replace the oil filter.

Use the correct filter wrench and remove the old filter. Turn it counterclockwise as viewed from the bottom end of the filter. In some cases the filter might be difficult to remove. This is usually because it had been over-tightened when installed. A good wrench and patience usually prevails but in some cases you have to drive a large screwdriver through the body of the filter to get it off.

Once the filter is removed use a lint-free towel and wipe off and inspect the filter mounting area. Make sure that the old filter o ring has been removed from the engine.

Compare the size and type of the threaded hole of the new filter to the old filter to make sure you have the correct type.

Coat the o ring on the new filter with clean oil.

Thread the new filter into place until hand tight.

Use the filter wrench to tighten another 3/4 of a turn and no more! Over tightening the filter makes it very difficult to be removed.

Look up your engine oil capacity in the owner's manual or on the capacity decal on the engine. Most inline 4 cylinder engines take 4-5 quarts. Most V6 engines take about 5 US quarts (5,000 ml). Most V8 small blocks take about 5 US quarts (5,000 ml) and Big Block V8's can take up to seven quarts depending on the exact model.

Fill the engine with the correct amount of oil. Newer Mer cruiser engines use a Color Coding System to locate and identify the oil fill cap and dipstick. Mer cruiser uses yellow to identify oil service points.

Let the motor sit for 5 minutes before checking the level on the dipstick. This will allow the new oil to drip all the way down into the oil pan.

Remember that the filter will hold some oil too.

After you are done filling install your oil fill cap and perform a general inspection on the engine. Make sure the filter has been installed and that you have cleared the engine area of all rags and tools.

Supply a water supply to the motor and start the engine.

Immediately inspect the oil filter while the engine is running. Look for any oil leaks. Go to the helm and observe your oil pressure gauge for a proper reading.

Let the engine warm up to operating temp.

Turn off the motor and let it sit for 5 minutes.

The manual that came with my mercruiser says to check the oil level with the boat "at rest in the water".

Remove and wipe off the dipstick and check the oil level again.

Add more oil if needed. In general one quart adds about 3/8" on the dipstick. This can vary from model to model, though.

Clean up your mess and go boating!