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Is Your Reverse Osmosis Watermaker Killing Your Marine Engine?

Topping off a marine engine's closed cooling system with Reverse Osmosis water can cause corrosion. Desalinated water can corrode an engine from the inside out.

desalinated reverse osmosis water can corrode an engine from the inside out a yanmar marine 6hym marine diesel engine

Believe it or not, a watermaker can kill a marine engine. Surprise: De-Salinated water is very corrosive. Watermakers with their reverse-osmosis membranes, scrub saltwater squeaky clean until it's fit for drinking. But when RO water is added to an engine's expansion tank to top off the coolant, the reverse-osmosis-generated water attacks copper and gray iron castings. Components like temperature senders literally dissolve in the mineral-starved water. Overheating and engine death can result.

One case history documented by Seattle-based Northern Lights/Lugger reveals how reverse-osmosis-generated water dissolved about a dozen temperature senders in a row before the warranty team figured out what the problem was. Here's something scary. There have been cases where cylinder liners eroded completely through in as few as 300 engine hours. But don't despair--there's a simple solution. According to Dick Gee of Northern Lights, "The only fluid that belongs in the coolant blend, besides antifreeze, is de-ionized distilled water."