3QM or 3GM should be putting about 3.5 gallons per minute at 2500 rpm.
out the wet exhaust discharge - use a bucket and stopwatch.

If not, then fouled or 'salted' exhaust manifold jacket, slipping
impeller due to worn cam lobe in pump, broken pump impeller downstream
of pump and lodged in the circuit, fouled inlet strainer, huge slabs of
rust breaking off inside exhaust manifold, or fouled or 'salted' water
injection elbow. My bet money is on a lodged broken piece of impeller
vane or fouled/salted exhaust manifold.

In article .com,
Whistledown wrote:

Hey all-

I have a 3 cyl. Yanmar that has been modded with a Freshwater cooler.
How much water is tolerable coming out of the exhaust?

thanks
b