Join Date: Sep 2010
Location: Boston area
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Re: flushing/antifreezing 2gm20f
Just a quick thought on your statement of adding "antifreeze mix". I don't think you should use straight, undiluted, anti-freeze, not premixed to 50-50, etc. The reason is that it is going to mix to some extent within the block/muffler, etc. as it pushes the water out. After say 3 gallons being pushed through, you should be down to nearly straight anti-freeze, and that raises another possible concern. The freezing point of straight anti-freeze is higher than properly mixed anti-freeze. I don't rely on using pre-mixed due to the inability of controlling how much water is in the final mix, and don't want anything to freeze either. Solution I use is to run the 100 degree anti-freeze in motor, not the much weaker 50 degree stuff that i use in water system, bilge, etc.. Costs a bit more, but don't need a ton of it and the undiluted freeze point drops quite low. Note that I store the boat in Maine, so low temperatures are often lower than most need worry about.
One other thing I do is remove the engine raw water thermostat to insure that all of the passages get flushed. Even if you warm up the motor before flush, as soon as the cold flush passes the thermostat, the thermostat starts closing pretty fast, blocking off parts of the internal passages. Since you should leave the system full over the winter to reduce internal corrosion from air, I just leave the thermostat out until spring, with a note on the ignition key to replace it.
1985 Marshall 22 catboat