I have a '77 Pearson 30 with the original Atomic 4 engine, raw water cooled. The exhaust system was replaced from the manifold out to the outlet at the rear of the boat three years ago.
During my pre-launch engine test, I ran into a problem I can not figure out. The A 4 started easily and ran well (and continues to do both). When the boat is on the hard, I use a 5 Gal pail and draw water from the pail through a hose and T-fitting. I noticed the engine was not drawing water quite as well as it normally does, although there was definitely water flow from the exhaust, along with some steam. As soon as the engine came up to operating temperature, water flow stopped, but the steam continued. Then, very shortly after, hot, cruddy water began flowing back into the pail from the engine. I shut the engine down and took note of the temperature gauge, which showed about 185 degrees, which is a good bit hotter than normal.
It had been a few years since the water pump impeller has been changed, so I did that (the old one was in good shape with no missing vanes) along with the shaft seals and pump gaskets. After that fun job was done, I removed the bypass hose from the outlet of the thermostat housing and got good water flow on starting the engine, so I reconnected it and got the same result: OK water flow, no water flow, then a backup of water into the pail. At this point I removed the thermostat and made another attempt with the same result. I have attempted an acid flush of the engine according to the recommendation posted here but there has been no change. Weak flow when cold, reduced flow as the engine warms, then the backward flow past the operating water pump. Through all this, the motor runs smoothly and sounds perfectly normal.
I also notice, after the engine has been shut off, water boiling up into the hose where water exits the manifold.
Any ideas or help would be greatly appreciated.
During my pre-launch engine test, I ran into a problem I can not figure out. The A 4 started easily and ran well (and continues to do both). When the boat is on the hard, I use a 5 Gal pail and draw water from the pail through a hose and T-fitting. I noticed the engine was not drawing water quite as well as it normally does, although there was definitely water flow from the exhaust, along with some steam. As soon as the engine came up to operating temperature, water flow stopped, but the steam continued. Then, very shortly after, hot, cruddy water began flowing back into the pail from the engine. I shut the engine down and took note of the temperature gauge, which showed about 185 degrees, which is a good bit hotter than normal.
It had been a few years since the water pump impeller has been changed, so I did that (the old one was in good shape with no missing vanes) along with the shaft seals and pump gaskets. After that fun job was done, I removed the bypass hose from the outlet of the thermostat housing and got good water flow on starting the engine, so I reconnected it and got the same result: OK water flow, no water flow, then a backup of water into the pail. At this point I removed the thermostat and made another attempt with the same result. I have attempted an acid flush of the engine according to the recommendation posted here but there has been no change. Weak flow when cold, reduced flow as the engine warms, then the backward flow past the operating water pump. Through all this, the motor runs smoothly and sounds perfectly normal.
I also notice, after the engine has been shut off, water boiling up into the hose where water exits the manifold.
Any ideas or help would be greatly appreciated.
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