"brianM" wrote in message
news
I know this is an old chesnut and has been well thrashed out in this
group, but I have group googled about this ongoing problem and none of
the answers quite fit. I had the outboard serviced recently by the
Johnson agent in my area, the thermostat was replaced and everything else
checked out, however the motor will only run at full throttle for 2 mins
before the overheat alarm comes on. I use a 50-1 2-stroke oil
fuel mix. Once throttled back to idle, alarm goes off in 2-4 mins. After
that
I can plane at about 2/3 throttle indefinitely The water pump indicator
at the top of the motor has a steady stream out of the hose at all times
and after the OMC warning goes off, the water stream is hardly warm let
alone hot.
I have checked for debris clogging the intakes etc. Motor is flushed out
with fresh water after EVERY trip. Spark plugs are correct model and
new. I don't think the motor is overheating at all, but I play safe
anyway.


Back about that time there was a service bulletin about changing the rubber
water deflectors inside the cylinder block. If they were ever overheated
they would distort and cause continuous overheating. I believe there was
something about replacing the temp switch with one that had a tan wire with
a blue stripe, if the original one had a solid tan wire. Salt deposits can
also restrict the outflow of water thru the cylinderhead cover passages

This, of course, is assuming that the pump, passageways, exhaust plates and
gaskets, and rubber water hose grommets are in good shape.

Bill Grannis
service manager