Finding the Right Mix of AntiFreeze

Posted by By Darrell Nicholson with Drew Frye at 10:30AM - Comments: (3)

July 23, 2014

The refractometer allows you to determine your freeze-point protection within one degree of accuracy.

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.

The refractometer can also be used to determine the state of charge in your wet-cell batteries.

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 it’s 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 battery’s 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.

Comments (2)

The freeze point of most -50F burst point products (the pink stuff) is actually between 0F and 10F, though it does not freeze solidly enough to cause damage until considerably colder... though in most cases not nearly so low as -50F. Engine coolants, either pre-dilute or 50/50 dilutions based upon concentrate, typically begin to freeze at -30 to -35F; an engine can be damaged if started while there is slush in the system. Just as importantly, the corrosion inhibitors in both winterizing products and engine coolants are formulated to work properly at the recommended concentration; use less and you invite corrosion and bio-fouling.

But we'll cover this in depth in the upcoming articles.

Posted by: Unknown | July 25, 2014 9:22 PM    Report this comment

Great article. This winter I double checked on the antifreeze in my Hunter 29.5 and the cheap tool I used said that I was only good to + 20 F. I almost had a heart attack. I bought a much better testing unit ($6.00 instead of $2.00) and found I was good to around -30 F. I must have one of those Pocket Refractometers. I also changed my antifreeze and flushed the system. I wish I had done it earlier as the antifreeze was not in great shape. Thanks, T. Martin - Lenexa, KS.

Posted by: TRAVIS M | July 23, 2014 7:38 PM    Report this comment


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