Finding the Right Mix of AntiFreeze


Finding the Right Mix of AntiFreeze

While the polar vortex was pummeling the northern states last winter (ahhh, remember those days?), Practical Sailor contributor Drew Frye was knee deep in glycol antifreeze and engine coolants. The range of tests he ran compared how well the myriad products on the market protect our water supply and engine-cooling systems from freezing, corrosion, and biological growth. The results are just now filtering in, and we begin reporting them next month (September 2014) with an in-depth look at antifreeze.

Although we found some clear differences between the various antifreeze products on the market, one of our most important findings was that how you use antifreeze is as important as what product you use.Even the best product, mixed with too much water left in the line, results in a blend with unknown and perhaps unsatisfactory performance. While this may not be critical in North Carolina, sailors in Wisconsin need to get it right.

Finding the Right Mix of AntiFreeze

There is only one way to do that; measure the glycol as it comes out the other end of the plumbing. A $10 hydrometer from the local auto-parts store will do this. You have to collect a suitable volume of fluid in a cup, and if there is any oil (which floats) or dirt (which sinks), the reading will be affected. Remember to first check the calibration with water; if its off, buy a new one. In the end, you can guess based on color.

Or you can buy a tool that will last a lifetime, can be calibrated (small hidden screw on the bottom side) to read within 1 degree of the true freeze point, using only a few drops, and will even read the state-of-charge on your batterys wet cells. We are talking about the pocket refractometer, which looks like a small spotting scope.

How does it work? In addition to changing the density of water, glycols, alcohols, and acid affect the way light is bent, and a refractometer can measure this change. To use it, the user places a few drops of the target liquid on the prism, closes the cover, looks in the eye piece, and sees a sharp line that can be read in seconds.

Pocket refractometers sell for $75 to $150 through many online auto-parts retailers.

For more information on this topic, I have addressed coolants and antifreezes in two previous blog posts. In one report, I cautioned against using propylene glycol in engine-cooling systems that have acetal plastic (often used in clear sight bowls for raw-water intake filters). In the other, we looked at the relationship between glycol content in your antifreeze and the level of protection against harm from freezing.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him by email at