I have a Yanmar YSM8, Single cylinder diesel that is raw water cooled. It was rebuilt in 2000. I bought the boat (Oday 27) in 2003, I have always had a problem where the water pump looses it's prime when I go over a wake or just pick up an air bubble. When this happens I can hear the tone change in the exaust, when I look out the back I see there is no water coming out. I shut it down, open the engine compartment to get to the engine side of the water pump, pull off the hose and drain out the water which is now hot from the cylinder and no water movement, then put it back together, fire it up and water starts comming out of the exhaust and all is fine until I get another bubble in the line. I have positive water flow at the intake side of the pump, and I have a new impeller installed. Any thoughts on this one??? thanks in advance.
Yanmar cooling system
- Thread starter windride2712243
- Start date
- Status
By losing its prime
I take that to mean that the line between the intake and the pump "sucks" air for a moment or two thus breaking the vacuum necessary for the pump to work. If I read the rest of your post correctly, to correct this condition you removed the water hose from the pump outlet and drain the water which re-establishes the prime in the pump? Unless I am reading and interpreting this incorrecly this is counter to all of my albeit limited experience with water pumps.
I take that to mean that the line between the intake and the pump "sucks" air for a moment or two thus breaking the vacuum necessary for the pump to work. If I read the rest of your post correctly, to correct this condition you removed the water hose from the pump outlet and drain the water which re-establishes the prime in the pump? Unless I am reading and interpreting this incorrecly this is counter to all of my albeit limited experience with water pumps.
Position of thru-hull
Sounds to me like the builder/designer of the boat put the thru-hull in a bad place. Is it centerline as low as it can go on the hull? How close to the waterline is the thru-hull? I would think that it should be mounted in a place that never comes out of the water. Was the boat built with the engine or did it originally have an outboard and was changed? Very mysterious...
Sounds to me like the builder/designer of the boat put the thru-hull in a bad place. Is it centerline as low as it can go on the hull? How close to the waterline is the thru-hull? I would think that it should be mounted in a place that never comes out of the water. Was the boat built with the engine or did it originally have an outboard and was changed? Very mysterious...
Right
You are correct, I believe someone put the sink drain hose on the engine cooling through hull and vise versa, the engine was connected to a 1/2" through-hull that was higher (closer to water line) than the 3/4" through-hull that is deeper and closer to center line. So last weekend I moved the hoses around. During a test run I could not get it to loose prime completely but it did at one point have less water than normal come out and there was steam coming out of the exaust and then after a few minutes the water was back and the steam was gone. I hope this fixes the problem. Thanks for your input, It makes me feel better knowing we were both thinking the same thing. I will re post if the problem continues.
You are correct, I believe someone put the sink drain hose on the engine cooling through hull and vise versa, the engine was connected to a 1/2" through-hull that was higher (closer to water line) than the 3/4" through-hull that is deeper and closer to center line. So last weekend I moved the hoses around. During a test run I could not get it to loose prime completely but it did at one point have less water than normal come out and there was steam coming out of the exaust and then after a few minutes the water was back and the steam was gone. I hope this fixes the problem. Thanks for your input, It makes me feel better knowing we were both thinking the same thing. I will re post if the problem continues.
- Status