Marine Antifreeze Problems: When Pink Antifreeze Freezes

Posted by Darrell Nicholson at 12:00AM - Comments: (12)

[Updated December 5, 2018]

There’s nothing like buying several $3 bottles of marine antifreeze to protect your $30,000 boat, then coming home to discover the unused bottles frozen solid in your garage.

The onset of winter always brings queries about the effectiveness of certain boat antifreeze concoctions. A couple years back we got a letter from Mark Baldwin, owner of a Seasprite 34, Ella, in Blue Hill, Maine. Mark sent us pictures of this Uni-Gard pink antifreeze (rated for -50 degrees) frozen solid, at -14 degrees. He was worried about what might happen to his boat’s plumbing and engine cooling system, which had been winterized using the same pink stuff.

Pink Uni-Gard antifreeze vs. polar vortex chill: Who wins this round?

It just so happened that when Mark’s query arrived, we were in the middle of testing various antifreeze formulas for their effectiveness. Uni-Gard pink antifreeze, which sells for about $3 a gallon at Lowe’s hardware stores and some marine chandlers, is one of the most common propylene-glycol formulas sold to boaters.

Uni-Gard pink is listed as having 25- to 35-percent propylene glycol, which should provide the -50-degree burst protection claimed on the bottle. Although it will technically “freeze” at temperatures as warm as 8 degrees, it should still be fairly soft and slushy at much lower temperatures, too soft to burst a pipe or hose.

If, however, there is a lot of water still left in the boat’s plumbing lines, the protection against freezing is diminished, and the antifreeze can become even less effective through each freeze-and-thaw cycle. Ideally, during the winterizing process, the marine antifreeze is flushed through the system to remove standing water from any low spots.

Protecting engines presents different challenges. As I graphically illustrated in an earlier blog on this topic, propylene glycol—the non-toxic antifreeze commonly sold to RV and boat owners—is not our first choice for protecting an engine’s cooling system. In our testing, ethylene glycol, the highly toxic (when ingested) antifreeze that propylene glycol replaced, is far less harmful to certain plastic, rubber, and nylon components in engine and plumbing lines.

Propylene glycol can harm components in freshwater and wastewater plumbing systems as well, but because ethylene glycol is not a safe choice for potable systems, there are no other antifreeze choices, other than draining the system. If your toilet's plumbing system cannot be fully purged and requires winterizing AND it is entirely isolated from your drinking supply, winterizing with ethylene glycol will be preferable, since it is less harmful to hoses, and plastic components.

Some sailors have suggested using Vodka as an antifreeze for potable water systems, but this turns out to be an expensive myth, and our tests have thoroughly debunked it. Not only will it burn holes in your pocket, it will turn your tanks and hoses into a fecund biome.

For those concerned about marine toxicity, an Environmental Protection Agency (EPA) study of chemicals used in airline de-icing operations found in its tests that neither glycol formula was particularly toxic to aquatic life. However, the EPA also cited several ways in which glycol can indirectly harm aquatic life by raising oxygen levels, etc. In our view, both formulas need to be used with care on land and near the water, and disposed of properly. Ideally, all glycols should be flushed and purged so that they can be captured for recycling.

Our research into the various marine antifreeze additives on the market has produced many interesting findings, among them the correlation between improper boat winterizing and a stinky water tank.

Probably the best article to start with is is our test highlighting our the formulas that are our Top Picks for Winterizing, which includes two important related articles. One is a Step-by-step Guide to Winterizing your Plumbing Systems and the other is an article on a handy tool called a refractometer, which offers proof positive that you've got enough antifreeze in your system.

Owners of auxilliary sailboats will surely want to read our test of Coolants that Fight Corrosion, as well as our PS Advisor on Engine Coolant Replacement.

Tips for How to Winterize A Boat

  • Never use ethylene glycol, which is highly toxic to humans, in potable water systems. The best practice is to drain the water tanks and lines of all water. When this is not possible, drain the tank and circulate propylene glycol only through the plumbing to ensure all low spots have been purged of water, then leave propylene glycol in plumbing through the winter. You should avoid adding glycol to the water tank or hot-water tank, as the glycol can attract biological growth.
  • Never use winterizing propylene glycol in the cooling system of a glycol-cooled engine. Diesel engine coolants are specially designed to prevent corrosion in the cooling system. Using a winterizing propylene glycol as an engine coolant can lead to internal pitting of the metal cooling jackets.
  • Some antifreeze formulas aimed at the RV market have ethyl alcohol in them that can damage PVC plumbing hoses. The ethyl alcohol can also cause sanitation hoses to lose their ability to prevent odors from escaping into the boat. Look for products with no ethyl alcohol.

Comments (11)

Recently made aware of a special diesel consideration. The explosive force of each cylinder causes small bubbles to form on the coolant side of the sleeve, diminishing heat transfer. Best to use a coolant specially designed for diesel.
What do you think??

Posted by: Capt Chetco | February 10, 2019 8:41 PM    Report this comment

Ask any "old timer" how it was done when owing a boat wasn't a big deal. All that was needed to winterize was a serious air compressor blowing out all the water lines in succession. Ditto with the engine followed by running cheap kerosene or even cheap oil to blow out the exhaust lines. Sure it will smoke a while come the spring. Life was easier in the old days. Especially when manual draining exhaust systems was standard practice.
And engines were built with servicing in mind. Now its all about "environmental friendly".
Boat yards make lots of monies repairing environmental friendly engines.

Norwalk, CT

Posted by: Piberman | February 9, 2019 9:39 AM    Report this comment

What about glycerine (= glycerol). It is recommended/mandatory for our watermaker. Your buy it in pharmacy.

Posted by: Charles | November 6, 2017 3:29 AM    Report this comment

Responding to Chad B.: I have never felt safe relying on heaters to prevent freeze damage to an unattended boat because of the possibility of power outages. I live and keep my boat in Arkansas, and the boat is about 90 miles from my house. We have only occasional hard, prolonged freezes, but they do occur, and power outages are more likely during the stormy winter weather that often accompanies them. In addition, hazardous travel conditions often occur at those times, too.

Posted by: frankwilson | November 5, 2017 12:18 PM    Report this comment

If you are building a new boat or making a major re-do. It is not difficult to design it to drain entirely into the bilge. On the cold water side, A simple valve, at the lowest place in a line which has a continuous down grade will do it. the shower head usually suffices as the air inlet vent.
On the hot water side, It may be more simple to drain the Waterheater tank separately, though It can also be the lowpoint drain if convenient.
Result is you save the mess, cost and work of annual change of fluid, no risk of freezing, and no chance of chemical damage to plastic fittings, nor of harm to the environment from improperly disposed waste chemicals.

Posted by: Capt Chetco | November 4, 2017 12:26 PM    Report this comment

Interesting article and follow-up comments.
It is fully applicable in North America, but what to do in Europe, where the propyl glycol is not available, or is available only in 45 gallon drums and 10 times the US price?
We used ethyl glycol for years for the piping systems, flushing VERY generously until all taste and colour was removed, then a bit more.
We installed valves to keep the anti-freeze out of the tanks.
We found that British and Norwegian sailors, RV suppliers, boatyards etc. had never heard of American "plumbers antifreeze"
Non-toxic antifreeze was available in reasonable size containers in Germany, at about 10 times US prices.

Posted by: NeilMcCubbin | November 3, 2017 3:40 AM    Report this comment

Interesting article. Thank you. You say "For those concerned about marine toxicity..."
Might I suggest you use a different phrase in the future -- "As for marine toxicity..." or something similar? Your wording makes it sound like an afterthought, or that not all of us should be concerned. All boaters should be concerned about how what we use in and on our boats affects the ocean.
Bruce Balan
s/v Migration

Posted by: BBalan | November 2, 2017 4:58 PM    Report this comment

Frozen anti-freeze at home would certainly not be a welcome sight if I just poured a ton of it into my boat! We at Caframo are a little biased, but keeping engine compartments at safe temperatures during cold snaps can also be achieved with an engine compartment heater like the Pali. I hope it doesn't sound too much like an ad, but the Pali and other engine compartment heaters can be a great alternative or addition to your cold-weather management plan prior to yearly winterization.

Thanks for the informative article!
Chad B. from Caframo

Posted by: Caframo Marine | November 2, 2017 3:32 PM    Report this comment

-50 or-100 or -200 Antifreezes are named according to the copper burst point. The name is NOT describing the temperature at which they will begin to form ice crystals.

The burst point of an antifreeze is the temperature at which a sealed copper pipe filled with the undiluted product will burst. Burst points are a standard created by the plumbing industry in the 1930s to indicate the relative strength of antifreeze. They have since become synonymous with the name of antifreeze products used for winter storage. Burst points help consumers choose the proper product based on the lowest expected temperatures for their specific area.

A freeze point is the temperature at which ice crystals begin to form in the undiluted product. Freeze points are the measurements given when using refractometers and hydrometers. Note: most refractometers provide readings on both a PG and an EG scale, so it is important to use the PG reading when testing PG antifreeze. Hydrometers are either made to provide PG or EG readings. It is critical to test this product with a hydrometer specifically designed to provide PG readings. Most hydrometers are purchased at auto supply stores and are designed for use with EG, so they cannot be used to test PG antifreeze. A PG refractometer will not give accurate readings for antifreeze containing alcohol and PG. Keep in mind that it is normal to see readings that may vary by several degrees from the product's stated freeze point based on ambient temperature or the age of the product. For example, the freeze point of A -50degreeF PG product may be somewhere around +12degreeF, but it is not unusual to see readings in a range of +12degreeF to +16degreeF. A -50degreeF antifreeze containing alcohol and PG will have a freeze point of +25degreeF, but it is not unusual to see readings in a range of +21degreeF to +25degreeF. Shake PG antifreeze well before testing as the heavier PG component may have settled toward the bottom.

Because the stored engine or water system is not in use, preventing ice crystals is not necessary, and to do so would require the use of a more expensive product with a higher PG content. As an example, if a -50degreeF PG antifreeze has a freeze point of approximately +12degreeF, a -100degreeF antifreeze may have a freeze point of about -42degreeF.

However, as the temperature drops the solution begins to solidify and expand, putting pressure on pipes that can lead to damage. This is why it is important to select an antifreeze that will provide burst protection appropriate for a specific region's lowest anticipated temperatures. Products providing lower burst point temperatures contain higher concentrations of PG and are thus more expensive, but they will provide the protection needed in the event of extreme weather. Note: Antifreeze containing alcohol and PG are not recommended for engine use; these formulas are designed for use in water systems.

Posted by: BillatStarbrite | November 2, 2017 1:18 PM    Report this comment

Under your "tips", you state: "Never use winterizing propylene glycol in the cooling system of a glycol-cooled engine. Diesel engine coolants are specially designed to prevent corrosion in the cooling system. Using a winterizing propylene glycol as an engine coolant can lead to internal pitting of the metal cooling jackets."
Are you referring to using Propylene Glycol as the coolant in the fresh water side of the heat exchanger, or as an antifreeze in the raw water side, or both???
Kent Robertson

Posted by: S/V Kristy | November 2, 2017 9:43 AM    Report this comment

There are other sources for 100% propylene glycol that is food grade U.S.P. Tractor Supply sometimes stocks it and also carries it. Refrigeration supply stores carry the pure stuff, though it may not be U.S.P. None of these will be pink, though refrigeration diluted products are often dyed blue. This gives you control over the concentration. For example, our watermaker needs >60% concentration for long term storage. And considering we were caught in Irma, and probably will not get back in the water this year, it may have proven worthwhile to store with propylene glycol rather than the chemical 6-month storage solution.
Keep in mind that propylene glycol/water solutions may form a slush at temperatures higher than the freezing rating. But the slush is not a hard freeze that leads to burst pipes. It may not lead to the radial pressure needed for pipe burst. The slush will flow through the pipe lengthwise relieving the pressure, especially if you have open valves.

Posted by: Locquatious | November 2, 2017 9:37 AM    Report this comment

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