This is straight from Mercury via a personal phone call to their engine technicians. Updated to include Mercury part numbers for the filters, NGK part and stock numbers for the plugs, and approximate prices.

http://articles.richardhartman.net/jetboat/mercurywinterization.htm

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Official Mercury Winterization Process for 240EFI Engine

In a small outboard fuel tank, mix fresh non-alcohol/ethanol gasoline with the recommended amount of fuel stabilizer and Mercury Quickleen. Add twice the normal amount of Mercury Premium Plus 2-stroke oil. (RLH note: Mercury calls this “witch’s brew”.)

Disconnect the main fuel tank hose from the engine’s inline fuel filter and connect the outboard fuel tank hose in its place. Connect water line to flush port and turn on water. Start and idle engine.

Run until smell of exhaust changes, indicating that “witch’s brew” has made it through the entire engine. Stop engine. Disconnect temp fuel tank and drain any remaining contents into main fuel tank.

Place a catch container below vapor separator drain plug, remove drain plug, drain vapor separator, and reinstall plug. Direct quote from factory tech: “You do not want fuel pooled in the vapor separator all winter long.” (RLH note: This is the first reference I’ve seen anywhere relating to winterizing the vapor separator.)

Restart engine with no fuel tank connected and wait until engine stalls. Remove key from ignition and disconnect battery. Do NOT turn key to “ON” or “START” positions again, as this will enable fuel pump.

Shut off water, disconnect from flush port, and wait for water to finish draining.

Reconnect main fuel tank hose.

Drain main fuel tank and leave empty. Use fuel stabilizer (Sta-Bil or Mercury Fuel Additive) if tank cannot be drained.

My own additions:

Replace fuel/water separating filter with new, empty filter. Mercury part number 35-18458Q4, ~$22.

Replace inline fuel filter with new, empty filter. Mercury part number 35-889615, ~$8.50.

In Spring, replace spark plugs after first full tank of fuel has been consumed. NGK part number BPZ8HS-10, stock number 3133, ~$6 each, do not substitute.

Note that these instructions do not include changing the front and rear jetdrive lube, which is a vital part of winterization that should be performed at the same time.

There are two lube areas on the M2: The front of the impeller shaft (where the driveshaft and impeller shaft are connected via a set of bevel gears) and the rear of the impeller shaft (inside the stator). To do this job you’ll need a metric socket set, large flatblade screwdriver, 1/4 inch Allen wrench, two bottles of Mercury Premium Plus Gear Lube, Mercury lube hand pump, oil drain pan, wire brush, thread sealant, antiseize, and blue (medium strength) Loctite.

Adjust the trailer jack so the ride plate on the jetdrive is level.

Remove the center (fill/drain) plug in front of the intake grate. Use a large flatblade so you don’t ding up the screw. Don’t lose the little fiber washer underneath the screw.

Remove the off-center (vent) plug. The lube will begin draining. Inspect the lube for white streaks or foam (indicates water) or metal specks (indicates wear in the bevel gears). Let the lube drain into the pan while you begin working on the stator lube.

Disconnect the steering and thrust reverser cables.

Remove the four bolts holding the steering nozzle and thrust reverser to the jetdrive. Remove the assembly and set it aside.

Remove the four bolts holding the stator to the jetdrive. The stator will probably “stick” gently to the wear ring for now.

Return to the front lube area. Screw the pump hose into the center hole. Install the pump into the first bottle of lube. Begin pumping. You’ll use all of the first bottle and some of the second. Switch bottles when necessary. Eventually, the lube will start coming out of the off-center vent hole, which has a tube inside; when the lube is full it reaches the top of the tube and comes down through the vent hole.

Reinstall the off-center vent screw with its fiber washer and a dab of thread sealant on its threads. Unscrew the pump hose and reinstall the centered fill screw in the same way. The front lube is done.

Return to the stator area with the drain pan. Position the pan under the front of the stator. Pull STRAIGHT rearward on the stator to release it from the wear ring. If it sticks, tap gently with a rubber or plastic mallet. Continue pulling STRAIGHT back until the stator slides off the end of the impeller shaft. Lube will immediately begin draining. Set the stator face down on the drain pan to finish draining. Inspect the lube for white streaks or foam (indicates water).

It is important to remove and reinstall the stator straight along the impeller shaft so the impeller seal is not damaged.

Once the stator has drained, remove the center hex screw from the tip of the stator cone. Turn the stator over and let the remaining lube drain out. There’s always a little residual lube in there and this lets it all come out.

Inspect the impeller and wear ring for nicks, dings, and damage.

While the stator is draining, use the wire brush to clean the threads of all eight screws removed from the rear of the jetdrive.

Once the stator is completely drained, gently reinstall it on the back of the wear ring. Reinstall the associated screws using a dab of thread sealant, antiseize, or a very small amount of blue Loctite. Tighten in rotation and don’t overdo it; you’re tightening stainless steel bolts into aluminum threads. The service manual has torque specs but I just use my judgement.

Reinstall the center hex plug with a dab of thread sealant. Remove the top hex plug. Insert the lube pump hose (it won’t thread, you’ll have to hold it) and begin pumping. Fill until the lube reaches the bottom of the fill hole’s threads. Reinstall the top hex plug with a dab of thread sealant. The rear lube is done.

Reinstall the steering nozzle and thrust reverser assembly using a dab of thread sealant, antiseize, or a very small amount of blue Loctite. Again, tighten in rotation and don’t overdo it; you’re tightening stainless steel bolts into aluminum threads.

Reconnect the steering and thrust reverser cables. Confirm smooth operation of both from the driver’s seat. All done!

Time to complete: ~2 hours the first time, ~1 hour once you’ve done it before.

do i need to put antifreeze in motor

N O The mercury equipped versions are self draining blocks... no need to put any antifreeze in... unless you need some on your garage floor because that is where every drop will end up.
Rj

Absolutely nothing for 8 years straight except Stabil in the fuel tank. The Merc is self-draining and runs carbon-free on Regular fuel. No new filters, no new fluid, no new sparkplugs. But, hey, feel free to fork over 3 or 4 hundred bucks to your favorite dealer or mechanic every Fall if it makes you sleep better.

Except for flushing, I've run mine in Colorado and South Florida for 8 years straight and still run the original sparkplugs and sacrificial anodes. Unlike my girlfriend, this is an almost maintenance-free design.

First of all, the materials cost about $100 per year plus a couple hours of your time. Not a bad insurance policy for a $10,000 engine.

More importantly, these things are clearly documented in Mercury's manuals as being standard maintenence items every 50-100 hours or once per season.

Do you know if you still have ANY lube protecting your impeller shaft's gearing? I **know** I do, and that it doesn't have water or other contamination in it to damage the expensive drive and impeller shafts and the bevel gears on each.

Do you know if you still have any lube in your stator? I **know** I do, and that it also doesn't have any foreign stuff in there.

Do you know if your very old spark plugs are gapped properly? I **know** mine are. Have you gradually lost power and MPG over those eight years without realizing it because the ECM is being tricked by out-of-spec plugs? I **know** I haven't.

Do you know if your fuel/water separating filter is rusty inside? I **know** mine isn't. Someone recently reported on a jetboating website (can't remember which) that his SportJet was having problems. He finally tracked it down to the original(!) fuel/water separating filter, still on the engine several years later, which was absolutely full of rust. Please note that the fuel/water separating filter is AFTER the inline fuel filter. The only thing protecting your injectors ($100+ each, times six) at that point is the final filter in the vapor separator, a part no longer manufactured by Mercury and that cost well over $100 when it WAS available. Are you comfortable gambling with multi-$100 components? I'm not.

It's your choice. As for me, I'm very comfortable spending ~$100 and a couple of hours to KNOW the status of my very expensive engine and keep it in prime condition.

Not a flame, just a point of view.

It's hard to believe you've done nothing in 8 years to protect your "$10,000" dollar engine. I see this all the time. Sensor's that are shot, turn key enrichment not working correctly due to a bad temperature sensor, causing it to smoke and foul plugs.

These engines must have yearly maintenance or in the long run, you'll find yourself looking for parts. Outside a dealership, have you tried to find parts for this boat? I only know of one respectable web site that is reasonsable and will not rip you off.

It is a total loss cooling system and because of the sensors that adjust the mixture to keep if from building deposits, it'll run for, as we see at the moment, 8 years without maintenance.

But, ...............you are going to greatly reduce the life of this engine. Taken care of, this engine will last upwards of 15 years without a major overhaul. Your engine? We don't know yet. Keep us posted in the future as to how this engine contiues to run. Cheers!

I just serviced my boat last weekend and was surprised that the plugs looked perfect and all had identical gap. I still replaced them.

The stator oil looked like the day it went in but the pump housing oil was a little more cloudy. Having checked these things, I have a good idea of what to look forward to in the coming year. Sure you can probably go 8 years without service but you better hope there's a tow vessel handy when the unknown hits you.