ASTM D1384 Serves as Model for Testers


Cavitation pittin

Samples were tested for corrosion protection following the ASTM D1384 Corrosion in Glassware method ( Samples were diluted to 33-percent glycol, dosed with ASTM synthetic corrosive water (similar to 2-percent seawater), continuously aerated, and heated to 190 degrees for two weeks. As a laboratory control, a reference coolant (ASTM D 3585) was also exposed to provide a baseline.

At the end of the test period, the samples were cleaned according to a specified ASTM procedure, dried, and evaluated for both a change in appearance and loss in weight. While this is not considered to be a definitive test of acceptability-extensive fleet testing is always the bottom line-it has a long history as a screening test. Because the test is run with synthetic corrosive water and because of the accelerated nature of the testing, it is best not to read too much into minor differences between products, so long as they meet ASTM specification.

All of the tested engine coolants performed well in the screening level test-literally 1,000 times better than raw water-but there were some differences in performance. Winterization products (-50 burst-point propylene glycol formulas) performed surprisingly well for products intended for much milder conditions; however, we do not recommend any winterization product for engine coolant service-and neither do their respective manufacturers.

Diesel coolants were tested for cavitation pitting by exposing cast-iron coupons in an ultrasound bath for four hours, simulating cylinder-liner ringing. Any evidence of pitting or freckling was considered to be a failure. The purpose of this test was to identify coolants that effectively combat cylinder liner pitting.

The very best coupons, not surprisingly, were from the heavy-duty coolants, specifically formulated to endure the sort of torture commonplace in a heavily loaded diesel engine. Though you might get away with any of the long-life coolants in diesel service, we still like the idea of using heavy-duty coolants in wet-sleeve diesels and in boat engines with severe duty cycles (commercial fishing boats, trawlers, anyone that runs long and hard).

We also tested the products freeze points; all concentrated coolants were properly diluted, and all concentrates met concentrate specifications.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. 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 at