Onboard Flushing System For Raw Water Cooled Engine

[Cresco750]

I've been thinking about rigging up some kind of fitting within the cooling system of my Mercruiser 228 (raw water cooled) / Alpha 1 which will allow me to flush the cooling system while the boat is on the water, and found this on ebay: http://www.ebay.com/itm/380371640835?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT I asked the seller how the incoming sea water from the Alpha 1's water pump would be prevented from entering the cooling system while the flush was taking place and his response was that with the engine at idle the pressure from the garden hose would create enough back pressure against the Incoming sea water to prevent it from being pumped, and therefor only the freshwater would be circulating. Does this sound right to you? I would have thought that a shut off valve would be required to stop the flow, or would this cause the impeller to cavitate and burn out?

 

[achris]

Nope... The drive impeller will pump... The only way to stop seawater running into the engine will be to re-direct it...

 

[Bt Doctur]

what you want to do is cut the hose and make up a block with 3 valves in the shape of a T1 v T2
----------------------------------------------------------------------------------------------------------------------V1 V2
the left side of the T1 is raw water in , small v is shut-off valve.V1, raw water discharge thru a thru hull fitting, V2 is fresh water inlet, T2 to engine.
close small v, open V1 and V2 to flush. close V1 and V2, open small v for normal cooling

 

[Cresco750]

I thought as much. So does the pumped raw water have to be redirected overboard or can it simply be stopped by means of a valve down stream of the pump? Would stopping this flow cause problems with the pump ( remembering that the outdrive is still submerged in the sea)?

 

[achris]

If you 'dead-head' the raw water pump you will either blow a hose or gasket or damage the impeller or housing...

Chris......