T&T: Keel-cooled generator overheating

[salty dawg via Trawlers-and-Trawlering]

Having finally fixed the NMEA interface between the Garmin 1040 XS chart
plotter and the Robertson (Simrad) AP35 auto-pilot on this big steel hull
boat (more on that in another email after sea trial Wednesday), we are now
stumped by an overheating situation on a generator.

The unit is a 25 KW generator (one of two aboard). I has its own
generously sized box shaped keel cooler and has suddenly begun to run at
about 210 F. No alarms or auto shut down occurred, but the owner elected
to shut it down the two times it overheated over the weekend. The intake
and exhaust piping to the keel cooler seemed equally hot, and the hull in
the area of the cooler was also very hot. That leads one the to conclusion
that the thermostat and circulating pump are working.

The expansion tank above the generator showed coolant at about half full.
There is only a pipe fitting and threaded cap for filling the tank and
thus no easy way to attach my cooling system pressure tester; besides; I
think there is a vent on the tank open to the atmosphere. So I think some
of the diagnostics one can perform with a pressure tester are out. The
tank it right up against the top of the engine room further complicating
the issue.

Oil on the dipstick looks good.

I am in a quandary as to how to how to advise the owner beyond tearing into
the engine and looking for a blown head gasket. Any ideas?

Rich Gano
Calypso
Panama City, FL
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[Sean Welsh via Trawlers-and-Trawlering]

On 09/15/2014 10:12 PM, salty dawg via Trawlers-and-Trawlering wrote:
> ... I am in a quandary as to how to how to advise the owner beyond tearing into

> the engine and looking for a blown head gasket. Any ideas?

You are right to suspect a head gasket or even a cracked head. One way
to proceed here without a teardown would be to send samples of both the
lube oil and the coolant to a testing lab. Tests run $15-$20 and can
provide a wealth of information. You could even send a sample of the
fuel off, although if the tank is shared with other engines, that will
be less revealing.

-Sean