Preventing the corrosion of outboard motors

Boating in both fresh and salt water causes an outboard motor to accumulate contaminants like mud, salts, and other minerals. While flushing the motor with fresh water will remove most contaminants, some may remain, leading to internal corrosion of the motor. This corrosion can continue to spread long after the boat has been removed from the water and can cause problems such as blockages in cooling channels to leaks in the cylinder heads. Fresh water can not remove corrosion and a specialised cleaning solution will need to be employed. An excellent choice is an outboard motor engine flush, complete with anti-corrosive and passivating additives.

Corrosion of metal begins when it becomes wet, and once initiated, it will continue to spread provided it is kept wet. Dissolved oxygen in the water oxidises the metal surface which leads to the formation of a layer of metal oxide on the surface. As the corrosion continues, the oxide layer swells and grows, which not only restricts water movement through the channels but also reveals the clean metal beneath to the corrosive environment.

Rinsing your outboard out with water alone can cause entrapment of water in small gaps, grooves, and crevices. This water will continue to cause the aluminium to corrode while the engine is not in use. Drying the motor is difficult and blasting hot air through the cooling channels can drive the water deeper into the gaps. The use of a surfactants reduces the surface tension of the water, causing it to run off in sheets rather than bead up. This prevents the metal from being permanently wet and thus halts ongoing corrosion.

Once corrosion has formed in the cooling channels, it will begin to restrict the water flow and decrease the efficacy of heat transfer from the motor. The same is true for mineral scales like lime scale which are formed when salt water passes over the hot metal. Water cannot remove these products alone. Lowering the pH using an acid can cause corrosion to the non-corroded metal and is also quite hazardous. The use of hydrotropes on the other-hand is significantly safer to both the motor and the user. Hydrotropes remove and dissolve both scale and corrosion product using a process called chelation, which is selective for the metal ions found in both scale and corroded metal, hydrotropes clear out the cooling channels while ensuring the non-corroded areas remain untouched.

Once the outer layer of corrosion product has been removed, the fresh metal beneath becomes exposed to the new environment. Active passivating coatings form on the surface of the fresh metal and form a protective layer. These layers are very difficult to oxidise, preventing corrosion from occurring even during operation, but also fill small gaps and crevices that would otherwise collect water.

Corrosion is one of the primary causes of premature engine failure of outboard motors and can cause permanent damage if not dealt with accordingly. Entrapped water doesn’t self-dry, it doesn’t remove scale or corrosion build up, it doesn’t repair previous damage or apply a new protection coat over the cleaned metal. One of the most effective way to look after your outboard engine, is the utilisation of an outboard motor engine flush, which incorporates a hydrotrope with anti-corrosive and passivating additives.

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