Features December 2017 Issue

Winterizing Wisdom from the Chemistry Lab

Each winter sailors must tackle the project of winterizing their potable water system. Our preferred method is to dry the system completely (see PS September 2014, “Step-by-Step Winterizing tips.” If that’s not possible we completely empty the tank and then treat the plumbing with the correct concentration of anti-freeze. The online version of this article provides all the details you need to carry out this process, as does the recent Inside Practical Sailor blog post, “The (Cold) Case of the Frozen Anti-freeze.”

cracked valves
Photos by Drew Frye

Expanding ice cracked this valve (above right). Ethylene glycol (on left) did far less harm than propylene glycol (right) to filter bowls.

One of the reasons we prefer draining the system is because of the potential harm to neoprene components caused by propylene glycol, the anti-freeze prescribed for potable systems. Some of the vulnerable components, such as water pump impellers, are hidden from view. Other times, the damage is plainly visible.

In lab tests comparing propylene glycol and ethylene glycol (used only for non-potable systems), we found that a clear plastic water strainer housing exposed to propylene glycol was so crazed that we could no longer see through it for inspection. The strainer exposed to ethylene glycol was also damaged, but the crazing was far less severe. Interestingly, in the bowl exposed to ethylene glycol, the crazing appeared several days later, after the bowl had been rinsed and dried.

Penny pincher: You can save money on anti-freeze by diluting 100 F rated antifreeze to the protection level you need.

Although this report focuses on potable systems, the caution regarding propylene glycol applies to engine cooling and other non-potable systems as well. Engine cooling pump impellers are often made of neoprene, as are some joker valves used in toilets. For these and other non-potable systems, ethylene glycol is a better choice. Be very careful not to confuse the two. Ethylene glycol is toxic to humans if ingested and should never be used in potable water systems.

Bottom line: Try to drain your potable system completely each winter. If you must use propylene glycol anti-freeze, make sure it is the right concentration and remove any neoprene components. Otherwise, you should plan to replace them in the spring.

Comments (2)

I've owned my Marshall Sanderling (Marshall 18) catboat, equipped with a 1982 Yanmar 1GM Diesel (raw-water cooled) for 14 years, and have always winterized the engine by using West Marine -100degree potable-system antifreeze. My cooling system is equipped with a Groco bronze bulkhead-mount strainer with a clear bowl, which I believe is made of polycarbonate (I sent them an e-mail asking what it actually is made of), and I've never had any issues with cracking, crazing or other evidence of harm. The o-ring seal seems to be fine as well. Likewise, while I normally change the pump impeller each spring, I have skipped a year here or there, and in any case the removed impeller never has shown signs of chemical attack.

Posted by: Catboater | October 5, 2018 6:05 AM    Report this comment

Major yards have long used a compressed air hose to winterize water systems. A portable unit with a 6 gallon tank for about $100 puts you in business.
And will do heads as well. Once upon a time every builder of a cruising boat always made sure a small compressor was aboard. Useful when varnishing and painting

Peter I Berman
Norwalk Ct

Posted by: Piberman | October 3, 2018 10:49 AM    Report this comment

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