manifold water leak v/s exhaust waterjacket leak, or BOTH

[alkaid]

Hi Don and Everyone,
Now that I've replaced the carb (Thanks Don for awsome prompt service!!), removed the Crank case emissions kit from Indigo, bead blasted the manifold, new gasket, new plugs, cap, rotor and thermostat to solve a carbon problem in the #1 and 2 cylinders, We have a new problem.
While cranking (prolonged) we filled the block and carb with raw water.(quite the expirence!!!)
Step 1,Checked this site, (Thanks again Don) followed the directions and thought we had eliminated the problem. No such luck.
She restarted, opened the thru hull, Pumping water out the exhaust. While setting the timing she died. WATER IN THE CYLINDERS AGAIN!
Step 2, Following Don's note, thru hull closed, mmo in the cylinders, we find the manifold won't hold air. Blowing in the forward feed from the thermostat while blocking the removed hose that feds the exhaust water jacketed pipe to the mufler produces air and water bubbling out of the exhaust pipe nipple we removed the hose from.
We took the liberty of testing the exhaust water jacket the same way Don said to test the manifold. She held air!!
That tells me that the Manifold is shot (Don, More business shortly) and raises the question- How does the air blown into the water side of the (shot)
manifold travel out of the manifold, up the exhaust pipe, into the muffler and
back down and out the water jacketed side of the exhaust where we removed the hose from?
Would not the air just travel from the muffler out the boats exhaust hose?
Again my old A4 has me confused.
Any thoughts sure would be appreciated.
Paul and Valery

[Don Moyer]

Paul and Valery,

Good question! It turns out that there is a bit more water pressure in the water jackets of the engine than there is gas pressure in the exhaust side of the exhaust manifold.

The Atomic 4 likes to see no more than 1 1/2 psi in terms of exhaust back pressure, while water pressure within the cooling jackets can run as high as 9 or 10 psi. This means that the water from the water jacket will enter the exhaust chamber, from where it has a straight shot into the exhaust ports.

Any exhaust gas that would find its way into the water jacket (perhaps when just starting the engine) would simply mix with the exhaust gas that is already moving through the exhaust system and leave through the back of the boat.

Don