Advise on cooling issue

[Hookshurt]

My B28 is powered by 2001 Marine Power 350 Vortecs. They are raw water cooled. I noticed this weekend when doing some work that the Starboard motor is not drawing water. I checked and it appears that the raw water intake is partially clogged, so I hooked it up to the freshwater flush and it still isn't pulling water through. I checked the impellar and replaced it, even though the existing impellar was in good shape. Still no change. I checked all the hoses and they are not clogged. I can hear the fresh water flow into the hoses and there are no leaks. When I first start the motor it blows the water out and then that's it. Sorry for the lengthy explanation, but I wanted to convey that I had done all the trouble checks I knew how to do. Thanks.

[Carl]

Blocked coolant passageway, initial thoughts would be from rust as you have strainers and pump vains where intact.

What used to happen with me, flakes of rust would get picked up and clog passageways as they narrowed. Shut motor they would fall back down, so when I started motor they pumped fine...for a little while till they went back up and blocked passagway again.

I used to backflush my motor, stick a thin welding wire in where I could and remove scale, a wire coat hanger could work too. Pull coolers and check for particles there as well. I used to remove drain plugs from block and have water gush out while sticking it. That would slow down the time it took in between problems. A quick fix was to just pull off exhaust hoses from risers and stick them as that was usually the area that gave the most problems.

When backflushing make sure you know where the water is going, make sure you do not have it back up into the engine. Not sure about all the precautions you need to take, but ask about your setup first if not sure.

If risers and manifolds are old, you may want to pull plugs before running/starting engine to verify they where not comprimised and leaking water into cylinders.

[Hookshurt]

THanks! I'll give it a shot.

[Capt Dick Dean]

I would close the intake valve where the raw water comes into the boat. Take the hose off the valve. Open that valve. The water should flow in big time. If it dosen't, then there is something clogged there. Time for a swim!

OR take the hoses off that goes into the risers. Start the engine and see if water is getting that far thru the system. IF the water is up to the risers then it's the risers/manifolds.

Taking a riser off is no big deal. When it's off you can see both inside the riser and maniflod to a degree.

UV always says start at the start and work your way thru. Sounds good to me. And so far things are pretty good.

[Hookshurt]

Thanks for the feedback and ideas. I got a chance to go down and try to put them to use this weekend. The final on this. Go back to the basics and make sure that the last guy who worked on the boat installed everything the right way. In this instance, hoses installed incorrectly. On the bright side, it is running, the barnacles are removed from the strainers, new filter baskets , new gaskets, and the list goes on (not to mention I have furthered my knowledge of how things work on this beast). THanks again.