Since we’ve been going to sea, mariners have realized the importance of removing saltwater. It is corrosive, oxidizes metals, and will eventually accumulate as scale, causing overheating, downtime, and serious damage to your engine. The best and easiest way to combat the effects of seawater in any raw water-cooled network is a freshwater flush at the end of its run cycle.
There are over 1.6 pounds of salt per cubic foot of seawater and an extraordinary amount of biologics. This concentration then runs through a narrow passage in your engine as it heats up to over 180 degrees and then cools. When you’re operating a motor without a flush at the end of each run cycle, these factors wreak havoc in those narrow passages with scale and corrosion. As time passes, this build-up will insulate the cool raw water and lessen the network’s ability to remove the heat from the engine.
Currently, routine preventative maintenance includes disassembly of the heat exchanger, scraping off the growth and corrosion build-up, and/or pouring acid over the components to remove hard scale. These methods can cause serious degradation in the metal cooling tubes and eventually lead to cooler failure.
As a result, some manufacturers are now recommending ‘inspection’ instead of ‘service’, whereas others simply recommend component replacement, but either way, there comes a time when those coolers are going to have to come off and be serviced. The downtime this causes can be significant and the costs can be high, not to mention the human error that can be involved in just removing, transporting and reinstalling the coolers.
This can all be avoided with a routine freshwater flush at the end of each run cycle while the engine is still hot.
This step is especially vital with an open cooling type system, such as those on outboard engines. If you evacuate the seawater out of the engine, introducing air, and then let the engine cool, it’s too late. Once the thermostat has closed, the salt and oxygen are already at work inside the seawater passages. A freshwater flush at the end of the run cycle ensures that the salt and the oxygen don’t have the time to begin their destructive process.
Now don’t even get me started about flushing inboard engines! We know that we’re supposed to flush outboards because there’s thousands of videos online and it’s in every OEM service manual. But “How???” is the first thing I usually hear when talking inboards. The fact is that flushing inboard engines is maybe even MORE beneficial to the boat owner than flushing outboards.
When an inboard engine is operated, raw water is constantly flowing through the cooling network. When the engine stops, so does the water flow. Unlike outboards, inboard diesels generate a LOT more heat, which has no other way to escape than through the heat exchangers. When the engine stops, the residual engine heat seeps into the water, making it REALLY hot, which causes the minerals and salts to precitpate out and stick to the walls of the heat exchangers. Additionally, there are always dissimilar metals in the network, and they are soaking in a conductive solution (salt water). Saltwater has a conductivity of about 50,000 microsiemens, whereas pure freshwater is between 0.5-3.0. Saltwater can be 100,000 times more conductive than freshwater. This condition invariably leads to electrolysis as a secondary problem within the raw water networks.
The only way to stop scale and corrosion in an inboard engine is to purge it and pickle it using fresh water at the end of every run cycle. Period.
My wife and I started our journey sailing a boat all through the Caribbean, and the only reason we stopped is because my engine scaled itself to death, and I couldn’t afford to replace it. I have personal experience with the pain of raw water system maintenance. I dare say, if I had a PHIBER System on that boat, I might still be out there today! Oh, well.
That was just where I started this journey. Since then, I have made my entire life in, on, and around boats. Today, I hold a 1600 Ton Captain’s license and a 4000 HP Engineer license, and I’ve operated everything from small beach cats to research vessels to motor yachts.
They all have one commonality: the rinse-down.
We all know the effects of seawater, and it’s long past due that we treat our engines and raw water networks the same way we treat the rest of our boats. A freshwater flush is the most effective way to maintain your equipment and stay ahead of deterioration, instead of keeping up.
