T&T: A coolant mystery

[Peter Arneil]

I9ve got a Volvo AMD41 diesel driving the same brand duo-prop outdrive;  850
hours, seven years old.  The boat is kept on the hard and the engine is
flushed after every outing, usually 2 - 3 days, but two long trips of 7 and
9 weeks, too.  So, it9s relatively new and has been very well cared for.

The problem is coolant that is showing up in the bilge in rather large
quantities, 7 - 8 gallons over one week-long stretch (~25 running hours),
WITHOUT needing to add any coolant to the system.  The only possible
explanation seems to be that raw water is invading the cooling system,
causing it to overflow.  The logical culprit would be the heat exchanger,
but I9ve taken it off twice and had it pressure tested by two different
cooling specialists...and according to those tests, there are no leaks.

The mechanic insists that the heat exchanger is the only place where
intrusion could occur.  All other explanations require a coolant leak that
would manifest in the reservoir level, i.e. cracked block, etc.

Any thoughts?

Peter
Bellingham, WA