How to Replace a Mercury Outboard Water Pump Impeller on a Mercury Optimax 200 Hp Outboard
Wednesday, September 24th, 2014
When you think about the design of the standard open style Marine Cooling system you have to think about the various items that can end up getting picked up by the water pump and end up inside of the motor. Depending on the conditions you operate your boat within its not uncommon for boaters to suck up plastic bags, grass, weeds, etc all of which can limit the amount of water to the engine. The most common way a boater realizes this happening is when the alarm sounds and they shut down the motor. However by the time the alarm sounds damage may have already occurred. Understanding that this damage is cumulative in many cases, it sheds light on the importance of maintaining a properly functioning water pump impeller and cooling system. Understanding that the water pump by design functions by utilizing a specific amount of “controlled” friction between the water pump body and the impeller. As the blades of the impeller are deformed the area changes which in effect allows the pressure to be lowered as the area inside of the pump changes from smaller to greater. This lower pressure differential is what allows water to flow in the direction from higher to lower pressure. Alas the functioning of the positive displacement water pump. However once water is limited to the water pump this friction increases exponentially between the impeller and water pump body which then introduces heat, and ultimately the breakdown of the water pump impeller. Once this happens the material characteristics of the impeller change and are such that it is no longer able to create the needed “low” pressure draw to pump water as it was designed.
Regardless of whether you run a Mercury Outboard Motor, Yamaha 4 Stroke Outboard, or Mercuiser Sterndrive motor proper cooling system maintenance is critical to the longevity of that product.