mr3dman

Ok, the hose that goes from the bellhousing to the outer transom and then to part number 23 in this picture could be your problem. You have to remove #23 and have a look at the hose there.

28Eliminator

If there is a sand issue it will also plug up some of the oil cooler viens. Check the oil cooler and if they are plugged with any sand it needs removed to get sand out.

Rdegeo4140

Sorry to say could be a head gasket. If the engine is salt water cooled and not flushed with fresh water after every use, the small steel gasket between block and cylinder can corrode. A simple compression test will tell. At idle no load and water cold. While you're under way,the higher revs force more combustion into engine. can't really overheat as long as a constant flow of cold water moves thru the engine. I suspect gasket because you seem to have a good water flow. With a sealed fresh water system you would overheat. I have 35 years with Chevy and although a more common problem on a 350 small block(4" bore), it isn't impossible for the big block. Either way I would definitely check before storage. If water left in a cylinder for too long, it will seize engine. Sometimes it will eventually blow into the oil. Oil will overfill and look like coffee w/cream. Also if hard to start sometimes it is because water is getting into a cylinder.

TomZ

iTrader: (2)

Solved. Bad pump. Heads were changed 50 hours ago.

Thanks everyone!!

Amarket Owner

I can tell you to cure the problem no question, but you must make checks.
1) Take off the water supply hose to the thermostat and let it dangle into the bilge. (not on anything that it will hurt) Now remove the output hose that comes from the rubber impeller pump and put the city water hose into there and clamp. Turn on the hose full on and notice how much comes from the t/stat hose. If it flows full and no pressure occurs where the water comes in, your hoses of your engine are clear. If limited flow of t/stat hose or pressure where the hose comes in, you have a clogged oil cooler or defective hose with internal flap restricting your water.
2) Put the t/stat hose back on the housing and re pressure the hose, now you are checking the hoses plus your exhaust passages. Once under pressure of city hose should see plenty water from the prop and exhaust relief passages, and no pressure where the hose goes into the pump discharg hose because high pressure there will indicate the water cannot flow easily through the elbows. If the pressure shows up remove the elbows and either clear or replace them.
3) The water pump may be at at fault.
With the output hose of the pump disconnected , remove the input from the plastic adapter on the transom plate and place it in a large bucket. With out the city pressure of a flushette, the pump even just about idle speed should empty the bucket and the output of the pump should produce a large amount of water. If not check for the impeller or the condition of theend plates on the pump body if the pump is a solid brass pump.
4) Bravoitis could be the problem.
While the plastic adapter is off for the previous test, put your flushette on the drive and pressure it up.
Look at how much water comes out of the fwd end of the bell to t/p hose through the transom assembly
and if the water looks limited this may be the problem.
with a light inspect the tip of the hose just behind the plastic adapter and see if the hose and internal hollow plug has been crushed and limiting the flow to the pump.
One of the four sections is causing the problem. Check them one at a time.
good luck Buddy

TomZ

iTrader: (2)

Already figured it out... and found a bad transom in the process. The water passage coming through the drive was pinched **** by corrosion. I went to install a thru-transom pickup, and drilled into confetti. Ouch.

I'm redoing the transom and stringers this winter.

Thanks for the note!