the FW side of the engine without running isn't the easiest thing due to the hard piping and convoluted construction of the system, but here is what I would do:
- remove the hose from the bottom of the expansion tank and use that as the entry point into the system. Pump your new freshwater into that pipe. Unscrew the cylinder drain cocks on the bottom of each cylinder and completely remove the plugs from the fitting to allow maximum flow. Just let the flushed water from the cylinders run into the bilge
. You can clean it up later.... During this step you will have some flow out of the small breather line connected to the circ pump. That's ok, just let it flow to the bilge
- now pump water into the line. This water will flow down to the circ pump, thru the circ pump and up to the bottom of the exhaust
manifold. Into the manifold, from the manifold into the two heads, from the heads down into the cylinder blocks and out of the blocks thru the opened drain cocks. Flush for a while.....
- now stop the flush and replace the drain cocks in the bottom of the cylinders.
- remove the two hoses which come out of the front outboard
side of the exhaust
manifold ( for the house hot water heater
?) and run new hoses from those hose bibs into the bilge. Pump your water. One or both of these might flow. This will force water from the cylinders liners up into the other side of the heads and out into the second half of the exhaust manifold. Let it flow a while.
- now you have flushed the entire engine, and you might have gotten some back flow thru the heat exchanger
via the small bleeder line at the top front of the exchanger. Probably this will be enough to clean the HE, but if not you might have to remove the pipes at both ends of the HE and flush it.
- Flush out the house hot water heater by pumping thru the two hoses which you removed from the front outside of the exhaust manifold.
Reassemble everything and fill with 50/50 antifreeze
mix for the balance of the storage
. When you finally start the engine, remember to top up the expansion tank as there will undoubtedly be some air pockets remaining from the fill that will need to work
their way out.