40 hp Mariner water pump problem

[alebrewer]

I need some help with my 1986 40EL Mariner. With the Outboard in a large garbage can of water, the water pump only seems to work only at higher RPM's. When I go from higher RPM's to an Idle, you can hear a psssssss, and the water flow stops and doesn't return until I rev the motor up again. I removed the lower unit, inspected the impeller, gaskets cover etc., and everything looks ok. I put it all back together and the same happened. The impeller, and all related parts were replaced 2 season's ago and the boat has been used for no more than 4 hours since.
I'm at a loss.....please help!
Thanks!

 

[diaric]

Re: 40 hp Mariner water pump problem

the impellor blades didn't look at all worn on the sides? after 2 years it should be changed anyway as an insurance. while it was apart you could have hooked water to the tube, flushed it and ensured that there were no blackages and it was flowing out telltale.

 

[tashasdaddy]

Re: 40 hp Mariner water pump problem

sound like an exhaust leak into the cooling system. impeller not putting enough pressure, and exhaust is stopping the flow of water.

 

[alebrewer]

Re: 40 hp Mariner water pump problem

I flushed the cooling system and blew it out with air......no change. I'm going to try it again when my new impeller arrives.
The exhaust leak sounds interesting.....how can I check this, what am I looking for?
Thanks for your help!