50hp 4 stroke problems

[JustinW]

I have a 2002 Merc 50hp 4 stroke that has been alarming at wot. I am under the assumption that it is an overheat alarm. I have replaced the impeller and changed the oil a week ago.

The problem is when running anything over about 1/3 throttle I get an alarm. The alarm doesn't occur immediately but goes off after I have gone about 100-200 yards. If I back off the throttle the alarm goes away. I have not had the alarm occur while idling, but I usually dont leave the motor idling for any long period of time.

Under the assumption that this is an overheating problem I removed the thermostat and did a boil test. The thermostat did not open and I do plan to change it. But in my thinking, shouldn't the motor overheat at idle as well if the thermostat is not opening?

[fivecows]

Is that the 4 cyl. motor? the rubber seal grommet at the top if the water tube coming off the water pump, up under the powerhead can overheat and destort to where it partially closes off the water flow. Will Idle all day long, but overheat when power applied. Might be worth checking

[JustinW]

Is that the 4 cyl. motor? the rubber seal grommet at the top if the water tube coming off the water pump, up under the powerhead can overheat and destort to where it partially closes off the water flow. Will Idle all day long, but overheat when power applied. Might be worth checking

I have heard about this problem from reading the past posts on this forum. That will be the last thing I check. I did find that the thermostat is stuck so I will be starting there first. Thanks for the reply!