On Sat, 10 Dec 2005 09:45:46 +1000, Billgran wrote:




"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

thanks for your reply and suggestions Bill, I'll take them to the Johnson
agent in the new year - they are pretty flat out at the moment with
last-minute forgot_to_get_my_motor_serviced types.

cheers
BrianM