I have a 91 searay with twin merc 350's. One motor was replaced 6
years back and the other I have replaced this year. After putting the
boat in the water this year I realize I have an overheating problem
with the brand new motor. I built it and have built many. Everything
was replaced on the new motor, manifolds, water pump. the only thing
that hasn't been replaced was the impellers in the lower units. I
didn't figure I needed to replace these since they didn't have 10
hours on them the year before when the engine went. The engine failed
because the manifolds let sea water in. Here is the question. What
kind of flow should I have coming up the lower units. I can fill a 5
gallon bucket in no time. No one I have talked to yet can give me a
definite answer. I think when you rev the engine the exhaust pressure
is overcoming the water pressure and causing the engine to begin to
overheat. It will idle for ever and the gauge never moves, but give
it a load and the temp climbs fast. Does anyone have a pressure spec
that the pump is going to have to put out?