How to Maintain a Mercury Outboard

Written by will charpentier
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How to Maintain a Mercury Outboard
Observing the maintenance intervals and procedures keeps your outboard working properly. (toy outboard motor image by pearlguy from

Mercury Marine offers a treasure trove of information--both in print and online--about properly maintaining your outboard, all of it to help you keep your boat in the water instead of in the shop. Mercury's maintenance recommendations range from the simple pre- and post-voyage checklists and clean up to inspections and adjustments after each 100 hours of use and 300 hours of use. The instructions for laying the motor up for the winter are specific and necessary to keep your warranty in force.

Skill level:

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Things you need

  • Garden hose
  • Flushing attachment
  • Marine lubricant
  • Gear case lubricant
  • Baking soda
  • Fuel additive (cleaner)
  • Zinc anodes
  • Hydraulic fluid
  • Anti-corrosive propylene glycol antifreeze
  • Fuel stabiliser
  • Fogging oil
  • Water pump replacement kit

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  1. 1

    Inspect the lanyard "kill" switch that stops the engine should you go overboard. Check all hoses for leaks or apparent damage that comes with exposure to sun and fuel. Look the prop over, checking it for dings and make sure the motor's transom mount is secure.

  2. 2

    Turn the steering wheel side to side through its full range to make sure there are no "tight spots" and that the wheel moves through its full range--know how many turns your wheel makes, "lock-to-lock."

  3. 3

    Flush the cooling system with a garden hose and the ear muff-shaped flushing attachment, particularly if operating in salt water or polluted water. Wash the motor down, cleaning off any salt deposits on the exterior of the motor, including the gear case--particularly if you operated in salt water. Remove any trash from the exhaust outlet around the propeller, and flush the outlet with fresh water.

  1. 1

    Find the lubrication points listed in the maintenance section of the motor operators' manual and lubricate them after each 100 hours of motor operation. If you operate in salt water, they need lubrication more often. Drain and replace the gear case lubricant and lubricate the splines on the driveshaft.

  2. 2

    Remove the spark plugs and check their general condition and their gap. Inspect the battery visually; if the posts have an acid build up, wash it away with a solution of baking soda and water. While flushing the motor, use an engine additive--available from your dealer--to remove engine deposits. Remove the plastic bowl from the primary fuel filter and dump the contents, if any.

  3. 3

    Inspect the zinc anodes--the "zincs"-- on the motor. Replace any that have lost more than 50 per cent of their original size. Check all bolts, nuts and other fasteners, including those on the steering link rods, to ensure they are tight.

  4. 4

    Open the power trim reservoir and check the fluid level. Cycle the trim system through its full range of motion with the hydraulic reservoir open and, if the fluid is low, add fluid and cycle the system. If, after the third cycle, the fluid is still low, inspect the hydraulics for a leak.

  5. 5

    Adjust the timing and carburettor. Mercury recommends this be done at the dealer or an authorised repair facility.

  1. 1

    Drain the raw water cooling system completely before laying your boat up for the winter. The motor operators' manual shows the location of the drains for your engine model.

  2. 2

    Fill the raw water cooling system with anticorrosive propylene glycol antifreeze. Change the engine oil and filter, inspect the electrical system, check the timing belt for wear, and complete a 100-hour inspection. Fill the tank on your last voyage and add a fuel stabiliser to the fuel.

  3. 3

    Remove the spark plugs and spray a fogging oil into each cylinder and into the carburettor. Turn the engine over a few times without starting it to circulate the oil. Change the water pump impeller at least once a year--the recommendation in the motor operator's manual is every 300 hours, unless you notice overheating or low water pressure.

Tips and warnings

  • Whenever you are in doubt about a maintenance procedure, contact your Mercury dealer to keep your warranty in force.
  • Failure to perform recommended maintenance puts you and your passengers at risk.

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