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15hp Merc stops peeing above idle

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docdoc88

New member
I have a 2000 model 15hp merc 2 stroke. The engine had water pump failure and over heated pretty good. I replaced the water pump - ( some fins were missing from the old one) put in in the water and it would pee at idle, but once I raised rpm's would stop peeing ... so I removed the pump and installed an OEM pump on it, I removed the rear cooling cover for inspection and replaced gasket, I removed and replaced the side - double plate exhaust/cooling cover and gaskets for inspection, I blew air the best I could to dislodge any debris. Compression test on both cylinders is 112 ...... put it back in water and same problem... idles fine and pee's water like a race horse .... once I start to raise rpm's it stops peeing and blows steam .... let it idle , engine cools to 120 degrees .... I have had the lower unit off multiple times to make sure copper tube and all is lined up. With the thermostat out - it wont pee water at all .... which is weird to me.
I am just wondering if when it over heated it did something in the engine to make the exhaust blow into the water jacket somewhere when you raise rpm's .... this engine does not appear to have a head gasket.

Thanks for any help
 
No ... boat floating in water..... pee's very strong at idle and does not overheat .... rev it up and stops peeing. lower unit has been apart multiple times. just replaced water pump with OEM unit
 
Well that is not right. The thermostat directly controls the pee stream on that motor , so there should be a significant difference in or out. Is the key in the impeller? Does water come out the exhaust relief? Did the old impeller come out in 1 piece?
 
The problem has been discovered. I talked to a boat repair place and told them everything I have done. Air test, gaskets, bla bla bla ... he said there has to be a restriction like a piece of something clogging up a passage way. So I got looking at everything and found one place I had not looked. There was a piece of rubber in between the little copper water pick up tube and the screen on the bottom the the foot. I took the screen off and the rubber fell out. Every time I rev'd it up ... it sucked the rubber up. When I replaced the pump, 3 of the fins where missing, the boat had been sitting for some time. I never thought of getting a flashlight and looking down in the foot. Put it in the water and works like a champ.. Thanks for all the brain storming !!
 
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