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Winterization for a merc 140 4 cylinder.


  • Add appropriate amount of Stabil to gas tank.
  • Remove lower unit oil fill plug and check for water contamination. If oil looks good reinstall plug. If oil is milky or water comes out, outdrive must be serviced to find bad seal.
  • Hook up water hose to ear muffs and attach to outdrive and make sure outdrive is lowered almost all the way down.
  • Turn on water at hose.
  • Start engine and let run for 30 minutes at ~ 1000 rpms.
  • Turn engine off.
  • Turn water off and remove ear muffs.
  • Remove motor plug, right side of engine near oil pan.
  • Poke thru with small screw driver to loosen up all cast and rust so the water flows out steady.
  • Remove the plug in the manifold, it is under the manifold ¾ of the way back towards the back of engine, poke it clear so the water comes out in a steady stream.
  • Remove the LARGE water hose in the front of the engine where it attaches to the thermostat housing.
  • Remove the incoming water hose and the small hose (that goes from the exhaust manifold to the thermostat housing) where they connect to the thermostat housing.
  • When the water has drained out of the block and the manifold reinstall the plugs. DO NOT over tighten them just good and snug.
  • Have 1 gallon of RV antifreeze ready, pour ¼ of it into the short hose and it will go directly into the exhaust manifold. Pour ¼ of it into the incoming water hose and make sure you hear it come out the outdrive!!! This back flushes the incoming water thru the power steering cooler if present and the transom assembly thru outdrive (you may have to raise the hose up several inches to allow the antifreeze to flow). Pour the rest into the LARGE hose that was removed from the thermostat housing, this goes straight into the motor.
  • Reinstall all the hoses and tighten the clamps.
  • Raise the outdrive to trailer position. NOTE: If the boat is to be stored outside exposed to rain/snow, LOWER the drive to prevent water from pooling and freezing in the lower casing exhaust passage.
  • Unhook battery and you are done!!

This applies to most 4 cylinder mercruiser engines RAW WATER (not closed cooling systems)

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