What hoses do you backflush through. When I follow from the seapump.....It appears to goto the power steering cooler then around to the oil cooler then to ???(heat exchanger)

Its a tight fit. My rib are sore, Arms bruised. had to take a break.
Had high H2O pressure. Sending unit is on the pwr steering cooler so I would assume it after that. Oil cooler.

I just changed the impellors last week.s Both (engines) were good. They were originals 140 hrs No blades missing. Maybe just some gunk up in the coolers or ???????

I don't have the answer but would like to know how it's done as well.

I take of the outlet side of the sea pump and the inlet side of the heat exchanger and flush toward the pump. Then take off both end caps on the heat exchanger and flush starboard to port. The rubber gaskets on the heat exchanger are reuseable just be carefull with them.

Using the intake line from to the exchanger, wrap a garden hose with some tape to help make a good fit inside the feed hose. Use a clamp to tighten it up. Then with your pump off and lhose open on the other end hold your hand over the hose to build up back pressure then release. Do this several times and it will help blast out any stuck debri.

All above are great point todo. I would add remove teh incoming hose to the oil cooler. The cooler is under the port manifold. Actually not that bad of a hose to get off. I then stuck my finger in the incoming side of the cooler. Yikes it was filled with gunk. seaweed etc... I then remove the hose from the main exchanger and back flushed the water into the cooler so water comes out the incoming end. I kept poking my fingers in there(oil cooler) to loosen things up.