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OMC Cobra outdrive water pump

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mbl1211

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1987 Cobra outdrive with 3.0L GM. Outdrive water pump is not getting water up to engine consistently when boat is in water, causing overheating. On my last trip to the lake it drew water for the first 20 minutes or so, then stopped and caused overheating. Impeller is a new Sierra one. and the cage, housing, steel plate and gasket are from Amazon and new. Impeller was inspected after overheat and is still fine. Hose from transom to water thermostat block is clear and I can back lush water down through transom and out of impeller area with no restrictions. Can also flush water from impeller area down through outdrive and out of the pickup holes without restriction. Lower unit was rebuilt with all new gaskets and new o-rings on the water pickup tube.

Water will flow through to engine with the earmuffs on in the driveway, but I know this is not a true test as the water pressure feeding the earmuffs does not replicate drawing water up the outdrive in the lake.

I'm thinking that the impeller is not creating the vacuum for some reason. It turns freely when boat is turned over. Maybe all the impeller pump pieces need to be from the same manufacturer/kit? I've heard that the BRP impeller kits are the best? But I have a heard time believing that the no name Amazon kits won't work.

Also, should the outdrive pump be able to pull water up out of a trough in the driveway if the 4 intake holes on each side are submerged? Looking for a way to test without going to the lake.

Thanks for any advice!!
 
Yes do not mix & match impellers & housings. I always use BRP impellers & housings ans no problems with them.
 
mbl1211 said:
Also, should the outdrive pump be able to pull water up out of a trough in the driveway if the 4 intake holes on each side are submerged?
Click to expand...
Nope,..... little to no suction, it's a flooded entry pump,......

I'd suspect a vacuum leak 'tween the drives pickup, 'n the pump,.....
 
Impellers do not “suck” water they move water when they are immersed in it. Do not run your boat with a trough because the impeller cannot pull the water up thru a column of air and will burn out if you do that. They are designed to be filled with water either by water pressure with ear muffs or hydrostatic pressure when you put the boat in the water.
 
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