achris
More fish than mountain goat
- Joined
- May 19, 2004
- Messages
- 27,468
Theory of Ops. V6 merc cooling system.<br /><br />V6 Mercurys use a high pressure-low volume water pump.<br /><br />The operation of the water pump is as follows:<br /><br />The pump consists of a housing, an impeller, a base plate with cutouts in it, and an assortment of gaskets. The impeller is offset in the housing towards the front. This creates a small chamber at the front with gradually increasing sized chambers at the back. As the impeller turns in the housing the chamber between any 2 blades is constantly changing. This is how the pump moves water. The opening in the base is on one side of the impeller and as the chamber gets bigger it sucks the water in. When the chamber approaches the back of the pump it reaches an opening in the housing that is connected to the water tube that takes the water up to the engine. As the engine speed increases the rubber blades start to fold over and the pump changes from a displacement pump to a centrifugal pump. The speed of this change-over is usually around 1800-2000 RPM.<br /><br />Cooling the power-head.<br /><br />Once the water leaves the pump it moves up the water tube and enters the exhaust plates of the engine. It moves between the inner and outer plate before entering the engine block through channels around the edges of the exhaust chamber. The water cools each side of the block and moves into the cylinder heads. Once in the cylinder heads it can take one of 2 paths depending on the output pressure of the pump. If the water pressure has reached the opening pressure of the poppet valve, located on the lower right hand side of the engine block, the valve will open and the water will flow through it and then spray into the exhaust tube as it leaves the engine. This full flow allows maximum cooling for the engine. If the water pressure is not enough to open the poppet, then the water will be warmed in the cylinder heads and block until the opening temperature of the thermostats is reached, usually around 140 degrees F. When the thermostats open the hot water can move through and out of the engine, again into the exhaust, until cooler water closes the thermostats. A small amount of water is allowed to pass the thermostats, through a small vent hole in it, in order to alleviate the problem of a pocket of cooler water around them not allowing them to open. <br /><br />At lower engine speeds the engine temperature is thermostat controlled, where as at the higher engine speeds it is pressure controlled. Usually in operation the temperature gauge, if fitted, will show a higher temperature at trolling speeds than at cruising speeds. This is to reduce the problem of fouling/oiling at low speed, due to too low an engine temperature. <br /><br /><br />Comments, suggestions, additions and beer are all welcome.<br /><br />Chris............
