T&T: Engine temperature

[Mark Richter]

Sid,
Your overheating problem has been found in a timely manner because of your
little high-power test run.  I perform a similar test about once every two
weeks on Pooh to make sure no incipient cooling system problems are lurking
to pop up at an innopportune moment.

First check the raw-water strainer for foreign matter.  Next pull the
raw-water pump and check the impeller, cover-plate, and the cam for wear or
missing blades.  any missing impeller blades will need to be found, normally
at the front edge of the heat exchanger tube-bundle.  Even if your impeller
is intact, blades from a previous impeller may be found there, blocking some
of the raw-water tubes.  If you have found any problems so far, it's time to
repeat the high-power test and see if the problem has been solved.

If not, the next job will be to remove the heat exchanger and clean the
tube-bundle with a small brass rod and/or muriatic acid, available at paint
stores or pool supply stores.  I use a tall bucket nearly full of 1 part
acid to 2 parts water, and dip the tube-bundle repeatedly from each end
until the copper or (hopefully) cupronickle tubes are bright and clean.  Use
heavy rubber gloves and wear eye protection.  Have plenty of fresh water
handy to dilute any splashes on your skin immediately.  Re-install the
heatexchanger, using new O-rings if they are used in your heat exchanger
assembly.  Check the condition of your water-injection exhaust elbow.
Corrosion here can sometimes block enough of the coolant path to reduce
coolant flow.

Occasionally, a rubber exhaust hose can de-laminate, and the internal
portion collapse, partially blocking flow.  This problem is hard to
diagnose, as the outside of the hose may appear normal.  A strong squeeze
along the hose may find an area that is spongier than the rest, and thus
suspect.

If all this attention to your cooling system's normal maintenance hasn't
corrected the problem, you may have a more serious internal engine problem
like a head-gasket leak, or a worn-out coolant circulation pump.  But the
cooling system maintenance outlined above will solve over-heating problems
about 90% of the time.

Mark Richter, m/v Winnie the Pooh
Mark's Mobile Marine