Below is my Winterization procedure. Use or don't but it is how I have done it for a very long time including to my own boat
Winterization for a Mercruiser V8 or V6.
Note 1: My method below describes how I winterize a marine engine. I personally do not change the engine oil/filter or outdrive gear oil in the fall. Have not for 30+ years.
Note 2 : The outdrive when it sits all winter in the cold, seals can go bad regardless if pressure checked in the fall or the gear oil is water free. If the drive is not serviced properly in the spring the gear oil could possibly leak causing extensive damage.
Proper outdrive Spring Service includes Drain and pressure check and check gimbal bearing and grease any fittings needing grease and new O-rings as supplied in gasket kit and grease the splined drive shaft and the two o-rings on shaft.
My winterization procedure: Done on trailer.
RAW WATER cooled only (not closed/fresh water cooling systems)
Add appropriate amount of Stabil to gas tank.
With Drive Down and allowed to sit for at least 2 hours so if any water present will flow to bottom of outdrive.
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/repaired by (pressure checking) to find bad seal before winter storage.
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. (this allows Stable added to gas tank to reach Carb)
Turn engine off.
Turn water off and remove ear muffs. (leave outdrive down for now)
Remove engine block water plugs, they are on the right side and left sides of engine near center of block and very close to oil pan, Typically Bronze material.(Could be two piece, Single plug, or Plastic winged screw type)
Once the plug(s) have been removed, Poke thru with small screw driver to loosen up all cast and rust so the water flows out in a steady stream.
Remove the plugs in the exhaust manifolds, they are 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. If Plastic winged type remove them and make sure water flows good.
Remove the two water hoses in the front of the engine where it attaches to the top of thermostat housing that go to Elbows. If No hoses go to elbows, Remove the two hoses at thermostat housing that go to bottom of Exhaust Manifolds
Remove the incoming water hose (the one coming in on the right hand side (oil filter side) that comes from the transom and goes thru the power steering cooler.
Remove the LARGE hose that is U shaped from the engine water pump to the thermostat housing (remove from the thermostat housing side only and after engine blocks has drained, twist the hose down towards the bilge to drain any remaining water out of hose).
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 two hoses that go to elbows or exhaust manifolds depending on what system you have and it will go directly into the exhaust elbows/manifold.
Pour ¼ of the RV antifreeze into the incoming water hose (SLOWLY) and make sure you hear/see it come out the outdrive intake ports!!!
This back flushes the incoming water thru the power steering cooler 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 of the RV antifreeze into the LARGE hose that was removed from the thermostat housing, this goes straight into the engine.
Reinstall all the hoses and tighten the clamps.
Raise the outdrive to trailer position.
Unhook battery and you are done!!
Note 3: When outdrive is in the down position it is self draining.
This applies to most V8 amd V6 cylinder Mercruiser Carbed engines RAW WATER cooled only (not closed cooling systems)
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