Winterizing Exc 343 Drain Heater Core?

[ExBuGuy]

Debating with myself if it’s really needed to drain the heater core if I’m running antifreeze through the motor anyway. Seems like whatever water is or was in there would be pushed out during this step making putting air through the system a redundancy. What day you fair people of planet nautique?

[Rednucleus]

These are really sensitive to freezing; I put a T fitting on my lower heater hose to allow me to drain the core and put the shop vac on it as well. It would also be a good place to pump in antifreeze if desired.

[bturner]

I'm far too nervous and don't care to risk the cash if something goes wrong with with the winterization process so I manually drain then fill with antifreeze per the owner's manual which includes the heater core.

For my process I use the attached diagram to drain the block. Once this is complete and with the drains still open, I blow out the line/heater core until no more water is heard draining into the into the J pipe. At this point I reinstall all the drain plugs. I then fill the heater core line with antifreeze and blow antifreeze through the system until I hear antifreeze entering the J pipe elbow. From here it's time to fill the block, I use the port at the top of the block to fill the block with antifreeze and will do so until I hear it coming out the exhaust. I'm typically just shy of 4 gallons using this method, which works for me.

I'm sure there's a hundred different ways to do all this but this is what has worked for me and what I stick with.

[SilentSeven]

+1 for being one of the first things to freeze.

To winterize mine, I disconnect the feed lines and just use my mouth to blow the line out. I then add about a cup of RV antifreeze to the line and blow it into the core. Even a little bit of water in the core can freeze in a corner cracking the core. Heater cores are not fun to replace.

Edit: FWIW, doing this work is 99x simpler when the engine is warmed up. Very easy to pull and replace warm hoses. Never fun to do when the engine a nice cold 40 degrees - hoses are hard as steel and super hard to remove. When warm, the heater drain procedure takes maybe 10 minutes max.

[swatguy]

I follow silent sevens method

[biacs]

Mine was leaking at the core, initially I connected the water hoses to just make a loop and bypass the bad core.

Eventually I bought a couple brass plug's for the water pump capped off from the heater core lines altogether :-)

In 5 years, I didnt want the next owner to get a surprise repair in the spring. We never used the heater, were more fairweather boaters!

[s_kelley2000]

From here it's time to fill the block, I use the port at the top of the block to fill the block with antifreeze and will do so until I hear it coming out the exhaust. I'm typically just shy of 4 gallons using this method, which works for me.

bturner I am very new to the 343 and just drained everything but I'd like to get some anti-freeze in there using your method for some extra piece of mind. Could you please describe a little more where you are filling the block from? Is that port under the cowling and it is a plug like the other drain plugs?

[bturner]

Mine has a heater so I use the heater port from the top of the block to pour antifreeze in the line going to the heater core then force it with compressed air (which in most cases is me blowing air into the heater core line). I have a 6" piece of heater line that I attach to the fitting on the block and with all the drain locations reinstalled, using a funnel on the hose , I pour antifreeze from there into the block. Since this is at the top of the block when you see or hear antifreeze coming out the exhaust you know the block and all the passages are fill with antifreeze, I use about 3.5 gallons to do this.

If you don't have a heater you can pull one of the lower hoses on the thermostat housing to do the same thing.