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Winterization process for Merc. 7.4 mpi
My previous mechanic retired and the new one in my area says they flush with antifreeze and then leave all drains and hoses disconnected. My previous mechanic left the antifreeze in the engine... I tend to agree with my former mech's philosophy in that it prevents internal corrosion and may help keep the hoses from drying out. I'm leaning towards doing the winterization myself but I want to be sure I'm on the right track. Any advise is appreciated. I know there are multiple ways of doing this but this is what I'm thinking.

1). I plan to pull all the blue plugs (5 in total) and drain the water making sure I plunge the holes with a wire or something to make sure there is no obstructions.
2). Replace the plugs.
3). Remove the thermostat and run the engine with a mix of 2 cycle oil, gas, and fuel stabilizer....... Suggestions on ration?
4). Along with #3 I will be hooking up the muffs and run the engine with marine antifreeze.
5). Replace the T stat after the antifreeze has circulated through. I plan to pour some into the hoses to fill them up if I loose any during this process.
That should be it, correct?

My reasoning for pulling the thermostat is to make sure the antifreeze has circ. through the engine. I could leave it in and just run the engine up to temp. but then I'll probably wind up in the burn unit as I try to remove those plugs reaching around a hot engine block.

I will replace the lower gear oil and engine oil in the fall. I pull the lower unit, grease and replace o rings in the spring.

Am I on the right track?

1) yes
2) yes
3) ?? Put a reasonable amount of 2 stroke oil into the fuel/water separator and run it until it smokes, then shut it down. May want to warm it up before you do this so you can change the oil afterward if you intend on changing oil in the fall?
4) Don't run it on the muffs with antifreeze because you can't guarantee it's circulating well. Don't remove the thermostat. Remove all the hoses from the thermostat housing and dump antifreeze into all of them until full, then clamp them back down. Be sure to remove the hoses from the raw water pump and drain them. That'll clear the water from the outside of the block.

I don't know if it helps, but I have to tow my boat back to the storage yard when I'm done. I think some jostling it around on the road will help the antifreeze distribute anywhere it didn't get while things were being filled.

^^^ What he said.

3. 50:1 ratio with Stabil added. Run it 5min or so. I usually change the fuel filter first so I know the mixed fuel is getting in. I use the same can I fill my leaf blower from.
4. Forget the muffs, Fog it, drain it, pull the hoses like mentioned and fill it with anit-freeze. No futzing with the thermostat, muffs, trying to fog and run in anti-freeze at the same time.
I also change the oil and gear lube at the same time.
I have used this method for years on both my Mercruiser and VP engines.

Do it this way and in the spring you are ready to go.

Good stuff!! Couple questions . Once I drain the hoses from the water pump do I reconnect them before pouring in the antifreeze from the top. And the raw water pump hoses are the two I pulled to change the impeller this spring…. Thanks again.

I reconnect them, but I don't think it matters, just something to remember to do in the spring.
I disconnect the big hose that runs from the thermostat to the circulating water pump - pour anti-freeze in to fill the engine block - reconnect.
Then disconnect the hoses that run to each manifold from the thermostat housing - fill each with antifreeze - reconnect.
On the VolvoPenta the raw water pump is right up front and easy to remove the hoses and drain. The Mercruiser is harder to get to, the Merc I winterized had Alpha's with the water pump in the outdrive, it just drained on it's own. Maybe someone with a BravoIII will chime in on how they do it.

The hoses might be a little different from engine to engine, but you get the idea.

Do you have engine block drains? Located on each side of the block below the heads. Open & rod these out as well.


Oh.... and it's WAAAY too early to start these discussions!!!

Holy Smokes wrote: Mon Aug 21, 2023 2:24 pm Do you have engine block drains? Located on each side of the block below the heads. Open & rod these out as well.


Oh.... and it's WAAAY too early to start these discussions!!!

+1

I agree with not running it on muffs with anitfreeze...just a lot of wasted antifreeze.

Pull plugs on engine
Drain manifolds
Drain raw water pump by removing hoses and the reattach
remove large hose going up to thermostat housing and put anti freeze into hose until anti freeze just starts coming out engine drain plug and reinstall plugs.
Continue filling antifreeze in the large hose and then reattach.

Done

I guess I'm not a serious as some.
Too much clock building.. when you only need to tell the time.

I've owned boats and other storable engines my entire life.
Run some Stabil through the injectors/carb, winterize the outdrive, and park it.
There is no need to run oil through the engine just to sit for a few months. It creates so many unnecessary issues.
Engines have sat abandoned in junkyards for years, and then plucked and reserviced without issue.