| Understanding the marine diesel engine cooling | | | | of the thermostat, which allows the coolant to |
| system is a necessary part of marine diesel | | | | circulate. |
| engine maintenance. | | | | Cooling system checks |
| Raw Water Cooling | | | | - To test your thermostat, boil a pot of water |
| Flexible impeller pumps provide an efficient solution | | | | and drop in the thermostat. (The water must be |
| to most raw water pumping needs. The primary | | | | 100°C--the thermostat usually opens at |
| advantage of a flexible impeller pump is that it is | | | | 85°C.) If the thermostat opens it is okay. If |
| self-priming, which means that when the vanes of | | | | it doesn't open, replace or clean carefully as they |
| the impeller are depressed and rebound, they | | | | can become sticky with deposits. Yanmar |
| create their own vacuum, drawing fluid into the | | | | thermostats can and should be regularly serviced. |
| pump. A dry pump can lift water up to as much | | | | Some thermostats cannot be serviced. |
| as three meters. Thus a flexible impeller pump | | | | - If the thermostat doesn't work, do not remove |
| being used for engine cooling does not need to be | | | | it and run the engine without it, as the engine will |
| manually primed or located below the water line. | | | | run cold and tight. You can drill a series of 1 |
| An added feature of a flexible impeller pump is | | | | 4Ë holes to give equivalent flow to an open |
| that it can pass fairly large solids without clogging | | | | thermostat. This will get you home, but you must |
| or damaging the pump. This reduces the need for | | | | then replace it. Be careful not to fit thermostat |
| filtration of incoming fluids. | | | | upside down. |
| For general or fresh water applications, a standard | | | | - Thermostat housings often corrode and need to |
| long lasting neoprene rubber impeller is used. | | | | be replaced. Some can be fabricated. |
| A general feature of all flexible impeller pumps is | | | | - The cooling system should be checked after 100 |
| that they cannot be permitted to run dry for | | | | hours running, or at least once each season, for |
| more than 30 seconds. Both the impeller and the | | | | leakage, deposits, etc. |
| seals require water for lubrication and will soon | | | | - The thermostat can be taken out of the |
| burn out if run dry. Parts that start to show wear | | | | housing on the front of the engine. |
| are easily replaceable and service kits are readily | | | | - The heat exchanger core should be removed |
| available for most models. | | | | bi-annually for cleaning and inspection. |
| Fresh Water Cooling | | | | - Many heat exchangers are fitted with anodes to |
| For circulation of the internal, closed, fresh water | | | | protect the expensive core. Check regularly. |
| circuit of the cooling system it is common to use | | | | - Check all hoses and clamps regularly. |
| a flexible rubber pump if it is located on the cold | | | | Replacing the sea-water pump impeller |
| side of the system (max. 55°C). Other types | | | | The pump impeller is made of neoprene rubber |
| of belt-driven centrifugal pumps are also used. | | | | and this can be damaged in the case of water |
| The closed circuit normally transfers heat from | | | | deficiency if, for example, the sea-water intake |
| the engine to the heat exchanger. The liquid used | | | | should be blocked. The pump impeller is changed |
| is water and anti-freeze. | | | | as follows: |
| Cooling Capacity | | | | |
| The required output of the cooling pump is related | | | | 1. Remove the cover from the sea-water pump. |
| to engine type and size, not to the size of the | | | | Note that there is the risk of water getting into |
| heat exchanger and exhaust system. This is true | | | | the boat. With the help of two screwdrivers pull |
| for both raw water as well as fresh water | | | | the shaft with the pump impeller out of the |
| handling systems. | | | | housing as far as necessary to reach the bolt |
| Temperature Regulators (Thermostats) | | | | retaining the impeller. Place some kind of |
| Thermostats are usually placed in the outlet at | | | | protection under the screwdrivers in order not to |
| the top of the cylinder head to prevent the | | | | damage the impeller housing. Alternatively, using |
| coolant from moving to the header tank until the | | | | channel-lock pliers, slide jaws between blades of |
| marine engine has nearly reached operating | | | | impeller, rotate and withdraw. |
| temperature. | | | | 2. Pull the impeller off the shaft. Clean the inside |
| There are different types of thermostats, the | | | | of the pump housing and fit the new impeller. |
| most common being the wax pellet type. The | | | | Always have a spare impeller on board. |
| capsule on the lower part of the thermostat has | | | | 3. Check that the pump coupling is not damaged, |
| a mixture of wax and copper (to increase the | | | | by trying to turn the pump impeller. Fit the cover |
| thermal conductivity) sealed in it. As the coolant | | | | with the original gasket, which has the right |
| temperature increases, the wax expands and | | | | thickness. |
| forces a rod to open the poppet valve at the top | | | | |