Merc 4.5, any reason I can't just dump the block and manually fill with pg antifreeze?

[void7910]

Going into my second winter with a Mercruiser 4.5 250hp. Last winter I winterized more or less "by the book" and drained the block, topped up the block with pg antifreeze by the topside blue plug on left of engine (looking aft), then ran on muffs to introduce antifreeze through the whole system. Using muffs I find I waste a ton of antifreeze.

Is there any particular reason I can't drain the block then pull the thermostat and fill the block/system manually? I used to do this on my old VP 5.0 and worked like a charm and only took 3 gallons of the pg antifreeze. Not sure if the new mercs absolutely require antifreeze to be introduced via muffs, for example the design of the new exhaust headers w/cats or other design of the system.

 

[Bt Doctur]

perfectly fine that way, just make sure you drain everything first

 

[Jmunk]

I have a 4.3L and fill with PG antifreeze via thermostat opening in intake after I drain all the water out.

 

[dave8311]

If there is no water in the block, why the need for antifreeze?

 

[matt167]

If there is no water in the block, why the need for antifreeze?

Corrosion is the reason that Mercruiser Added it to the manual.

 

[dave8311]

Corrosion is the reason that Mercruiser Added it to the manual.

Ok, didn't know that. Thankfully where I live I don't have to winterize

 

[Lou C]

My brother had one of these (Merc 4.5 200 hp) and what we did was drain it fully and then filled it with -100 marine antifreeze via the vent opening on the left side of the engine, till it ran out the outdrive water intakes. Took a while but no problems doing it that way.
On my old OMC, I just drain everything manually and then disconnect the big hose at the 'stat housing and then fill it till AF spurts out the 'stat housing neck. Re-connect hose and you're done. Not really a fan of the newer engines myself, more to go wrong and when it does more expensive and a headache to fix. I like old school and simple.....

 

[Cortes100]

One of the issues with the 4.5L is the thermostat housing is on the back of the engine. I couldn't even see it or touch it so that was not an option. If you have access to the housing it should work just like the older 4.3's.
The manual does say to drain everything first and then run on muffs, the dealer where I bought also did it this way.
I also tried draining the system, and then filled AF via the vent on the crossover tube on the front of engine, worked ok.
The 4.5 was a great performer but I sure don't miss doing the winterizing on that thing.
.

 

[Lou C]

Yep, my brother traded his 2020 Chap with the 4.5 I/O on a 2024 Chap with a Yamaha 4 stroke OB. I basically told him because we are in salt water sooner or later that one point drain will clog up due to the way cast iron corrodes, and then he'd have to clean out the drains which on these modern boats, is a horror show because there is no access. Even to change a starter, or God forbid a steering actuator, you'd have to pull the engine. At that point, the higher initial cost of the outboard, becomes well worth it. Between the EPA and cat converter exhaust and the boat companies who don't give a damn about making boats easier to work on, I/Os are dead around here.