6hp weird water pump issue

[kbait]

6R-72D. Replaced impeller due to overheating (customer said.. I just replaced). Old one was set pretty bad. Checked flow up to pump, no restrictions. Ran in barrel, and no water for 30 seconds.. then strong stream (waterpump completely submurged in water). Weird thing is, when I rev it to high idle, it stops pumping (at least discharging), head gets warm..and warmer.. Slow the throttle to idle and it starts pumping and discharging again.. scalding at first, then just warm. I figured maybe thermostat, so I removed the stat, screwed the stat cover back on and tested again. Same issue.. no water expelled w/exhaust at high idle, and overheating until slowing idle down, then scalding water, then cools down quick (no tstat). Never seen anything like this before.

Any clues? Thanks in advance, and have a great day!

 

[nwcove]

Re: 6hp weird water pump issue

saw a similiar issue with a 4.5 johnson....not in a barrel tho, on the lake. motor was good at slow idle....but tell tale was a bit hotter than normal, just a bit more throttle and tell tale was spitting water and steam.....very hot. turned out to be the head gasket.

 

[AlTn]

Re: 6hp weird water pump issue

I'm with nw, sounds like an exhaust leak into the cooling system is pressurizing it preventing the flow

 

[kbait]

Re: 6hp weird water pump issue

Thanks! That makes sense. I'll throw in a new head gasket after confirming flatness of mating surfaces, and post back w/results.

 

[kbait]

Re: 6hp weird water pump issue

Changed out head gasket, and noticed the intake screen behind prop was clogged (upper vent holes ok). I cleaned that out before test, and it pumps/cools beautifully now. I think it was the clogged screen, as the old head gasket looked to be sealing. Thanks!

 

[AlTn]

Re: 6hp weird water pump issue

yeah, that would make a difference....get's difficult to remember the checklist at times

 

[kbait]

Re: 6hp weird water pump issue

Yeah.. I first blew air w/hose into port under waterpump plate, and it flowed fine.. through the side vent only apparently. I'll remember to check that screen in the future!!