Hello Today on the first trip out for the weekend on the boat I got about 5 minutes out and the engine over heated. Spent the next 3 hours trying to figure it out before towing the boat back in with the dinghy. Another 2 hours at the dock and still no luck. Perhaps someone can help.
First it is a Yanmar 3GMD with is a raw water cooled engine. Here is what was tried. 1. When the alarm went checked that indeed no water pumping was the issue and turned the engine off and dropped an anchor. 2. Checked from the through hull to strainer and it was fine, no blockage. 3. Checked downstream of the pump and found no water. Thought, "that was easy". Not. Took the pump off and the bushing on the impeller had given up and the impeller wasn't spinning. It is only a year old, but whatever, put a new one in. Now water was coming out of the pump but still not going through the engine. Wondered whether back pressure from a plug downstream had caused the impeller to fail. 4. Systematically went through every location that you can check all the way to the riser on the exhaust and everything was clear. The riser is brand new and there are no blockages there. You could blow freely through hoses and the engine. Water was coming but not enough water. 5. Tested the thermostat in hot water, it opened no problem. 6. Started at the beginning again and this time ran the engine a bit at each spot. What we found was that the water would be fine until we rev'd up the engine and which point the water would slow down and stop. When we went down to an idle it would start again. This could be repeated over and over again. Except immediately downstream of the water pump where there was always water with pressure. 7. Took out the thermostat and tried this test down stream of it. Same problem. We assumed in the case the water, or at least not all of it, wouldn't even be going through the engine. 8. Flushed water forwards and backwards through the engine. No problem and no debris. 9. Figure there must be air coming at the strainer and put in a new gasket and checked for cracks. Same problem. Opinions are: 1. There is still a problem with air somewhere before or in the pump. But where? And why no water. 2. At the T where water goes into the cylinder jacket there is something wrong going on, but it is not easy to remove. 3. If it is a blockage in the engine then when there is no thermostat in the engine these symptoms should not occur downstream of the thermostat, but they do. 4. If it is in the engine, when the thermostat is in and the engine is cold you should get water, but you don't. Tomorrow we will start again, but if anyone has any ideas it would be appreciated. Don Jonsson Swan Song, C&C 34 Victoria Sent from my iPad _______________________________________________ This list is supported by the generous donations of our members. If you wish to make a contribution to offset our costs, please go to: https://www.paypal.me/stumurray All Contributions are greatly appreciated!
