Gone Outdoors

How to Service Mercruiser Outdrives

by Norm Rogers

A boat is a major investment for most people. To get the most out of your investment, and to keep repair costs down, service of the Mercruiser outdrive can be performed by the experienced do-it-yourselfer. Be sure to have a repair manual unique to your boat model and year. Servicing can be broken down into annual service, and service to be performed every two to three years.

Annual Service

Grease the propeller shaft by first removing the prop nut and associated hardware. Pull the prop straight off. Remove the thrust hub and liberally grease the prop shaft. Inspect the prop for damage. Get the prop rebuilt if needed.

Replace the gear lube by removing the filler plug near the bottom of the drive and the vent plug near the top. Allow gear lube to completely drain. Inspect the gear lube for moisture or metal filings. These are signs of damage to the unit. Fill the drive with new lube by pumping it into the bottom hole. When full, replace both plugs.

Clean the outer surface of the drive and touch up any nicks in the paint. Use Mercruiser paint and primer for this task.

Service Every Two to Three Years

Remove the out drive by first disconnecting the tilt cylinders and then remove the six nuts that secure the drive to the bell housing. Pull the drive straight back.

Inspect the U-joints and gimbal bearing. They need to be replaced if noise or stiffness are noticed. Inspect the bellows. If they are stiff or damaged, or if moisture is present inside, they need to be replaced.

Check the engine alignment by inserting the alignment tool. If it does not fit easily into place, the engine needs to be realigned.

Replace the impeller in the raw water pump. This is done by separating the lower unit from the outdrive and removing the water pump cover. Pry the old impeller out with a screwdriver and replace with a new one.

Items you will need
  • Socket set and socket wrench
  • Screwdriver
  • Drive gear lube
  • Prop shaft grease
  • Allen set
  • Replacement parts if needed
  • Repair manual (recommended)


  • Exercise caution when removing the drive. It is heavy. During reassembly, always use new gaskets and approved gasket sealer.

About the Author

Norm Rogers is an experienced writer, publisher and blogger. His works range from formal business documents to books and articles on travel and leisure. He now make the Twin Cities his home.