|Most cases of overheating are caused by
failed sea water intake pumps. On an Alpha drive, this pump is in the
drive. Inboards, Bravo, TRS and all the Speedmaster drives have a separate
intake pump on the engine.
||Of course, you should never overlook the possibility
that the water intake is plugged. If you have a through drive pickup
like an Alpha or Bravo, even thought it is not likely it is possible to
pick up a plastic bag that will cause a mystery overheat. When you stop,
the bag drifts away causing severe hair loss as you pull it out trying
to figure what happened.
|Especially with transom or bottom mounted
intakes sea weed or sand can make it all the way to your sea strainer (assuming
you have one) and plug it up solid. One of our customers with a Bravo
drive just told us that the opening for the water intake hose was
corroded almost shut!! So pull the drive and take a look.
||In any case if the intake pump has been starved
for water for more than a few seconds it is likely that the rubber
impeller inside has been damaged. These impellors also fail simply
because of age.
|A bad impeller will occasionally shed some blades. It is important
to trace the water flow and find all the pieces.
||In most cases the thermostat is not the cause
of the problem, but it can be damaged by high heat. A bad thermostat
will overheat the engine, but there will still be plenty of water coming
out of the exhausts.
|Clogged exhaust manifolds or
risers (elbows) can restrict the flow of water enough to reduce the flow
through the engine. This is most common in salt water. Rust accumulates
and eventually clogs the water passages. In fact, it is best to replace
risers and manifolds every few years to eliminate this
||It is possible to monitor the condition of
your risers by simply touching them with the engine running. MAKE
SURE THE ENGINE AND RISERS ARE COOL ENOUGH TO TOUCH! Assuming
your sea water pump is good, a clogged
riser will be noticeably warm to the touch.
|Even though it is unusual, we have
seen circulating pumps where the cast impeller is corroded so badly that
the pump no longer pumps. If this is your problem there will still be
plenty of water flow out the exhausts.
||Last but not least, excessive
steam behind the boat is usually the result of a water leak in to
the exhaust. This could be as simple as bad gaskets between the riser
and manifold or could be something more serious. It is common for a manifold
to crack after it has been overheated.
|After you have fixed your over
heating problem, here are some other
things to check