Mailport March 2014 Issue

Mailport: March 2014

Frozen Antifreeze

Photo courtesy of Mark Baldwin

When reader Mark Baldwin found that the antifreeze he had used to winterize his boat had frozen, he was understandably concerned about the fate of his boat's systems.

I used Uni-Gard pink antifreeze (rated for -50 degrees) to winterize my boat. The leftover jugs all froze solid at -14—or perhaps they froze before the night got that cold. The consequence for my boat’s systems? No telling until the spring, I guess.

Mark Baldwin
Ella, Seasprite 34
Blue Hill, Maine

It is completely normal for -50-degree antifreeze products to freeze at about +10 degrees. Squeeze the bottle or remove the lid, and insert a knife. What you will find—we hope—is that it’s only slush, not solid ice. Presuming there is no water dilution in your pipes—there shouldn’t be if you drained or blew out all of the water first, or let the glycol run for a bit—you should have burst protection of metal parts to -50 degrees and plastics to about -20 degrees. If there was 25-percent dilution, you may be in trouble; much depends on the geometry of the piping.

For more on winterizing products, check out the Feb. 3, 2014 blog at, and look for a series of PS articles on antifreeze and engine coolants this summer and fall. We will be testing products and exploring topics including burst point, corrosion, and how to avoid foul potable water from winterizing.

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