How To Winterize A 40 Hp Mercury Outboard.

Posted in Crank, Oil and Piston
  • I have a older 40 hp Mercury outboard. I picked up the boat and motor during late summer. But I haven’t had a chance to put it in the water yet. I had it started and ran for a short bit when I bought it to make sure it ran. Well winter came up real quick and it’s gonna be real cold here tonight.
    How to I winterize the engine ass far as a basic winterizing. I know I have to drain the lower end oil and replace that. But I am unsure about any water that maybe in the motor.
    The guy I got it from just said I had to change the lower gear oil, but online I see something about flushing the cooling system and fogging the engine.
    My mother whom use to know some stuff about boats said there is a drain plug for the water. Is this true? What do I have to do aside from the oil?

    There are 2 Answers for "How To Winterize A 40 Hp Mercury Outboard."

    1. Joe P says:

      Outboards are self draining. They don’t have water drain plugs. If the gear case has a lot of water in it due to a bad seal, freezing could cause damage. That is fairly unlikely but if you want to be sure, just remove the screw at the bottom near the prop to drain the gear case oil. You will also need to remove the vent screw located roughly 6 inches above the lower one. The only reason to flush an outboard cooling system is if it has been run in salt water or taken in a lot of silt by running in very shallow water. Remove the spark plugs and squirt oil (fogging oil is good) into the holes. Spray it up and around inside the holes. Pull on the starter cord to move the pistons, spray again. Unless you unhooked the gas hose and ran the engine dry when you last ran it, you should drain the carburetors so the gas doesn’t gum up. Look for a small plug to remove at the base of each carb. There probably is a little fuel filter gizmo with a thumb screw on the bottom. It is located at the other end of the fuel lines that feed the carbs. Remove the twist screw, swing out the retaining clip and catch the the little bowl, empty it of any gas and put it back together.

    2. jims says:

      Joe P has got it. I would like to see you change the fogging procedure a little. Instead of just spraying the oil in the cylinders, run the engine up to about 2500 rpm, and spray fogging oil into the carbs until the engine stalls. Then pull the plugs,etc, etc. The reasoning behind this is that this will protect the connecting rod bearings, which are usually the cause of internal breakdown.