2001 Mercury 50 hp ELPT bogs

[halfpint1]

I have a 2001 Mercury 50hp ELPT 4 stroke . I don't know too much about outboards . We bought this boat about a year ago used. The motor starts great and it was a little rough around 3000 but usually runs well around 4500/5000rpms tops. The last couple times we've had it out its been rough running on 4200 tops. Its to the point now where it doesn't want to run any higher than 2500 and when I try to give more throttle it starts to die out . There was a steady beep when it started to die and it stopped when I throttled down. There was a steady water flow from the engine while running and I checked the oil level which was fine. Any idea on what could be happening?

 

[Texasmark]

Steady beep is over temp. The thermostat opens around 143F and the OT sensor is set to 195F. If you are hitting the OT horn, your engine is too hot and slowing down because of mechanical seizure. Just because you had a pee stream doesn't mean things are ok in the engine. Need to check your thermostat for proper operation, the pop off valve if you have one which opens at around 2500 rpm and increases the cooling water flow, and last but not least the water pump, impeller particularly.

 

[halfpint1]

Took the boat to the mechanic and he replaced the temp sensor which corrected the problem as far as the motor wanting to die out. However he said that the motor was bogging at around 4500 rpms and he thought it needed a new prop.to correct it so he replaced the old prop (the old one had 3 wings(or whatever they are called)--the new one has 4) Took it out when we picked it up and the thing worked great--power up to 5500rpms. no dogging out .Quick take off etc. Noticed some kind of oil around the bottom of the motor shaft when we went to dry dock(looked like it could have ran down the seam in the back). Wiped it off thinking it could just be a one time thing . Later that same evening when I went to go fishing there was a little more oil around the bottom seam so I decided to go for a quick trip out and decided to call done when I figured I might make whatever is wrong get worse. Wiped it down again and checked it the next morning and there was a definite streak that had ran down the lower end onto the gravel. Took it back to the mechanic who just called and said he checked out the seals and couldn't find any reason for the oil to be leaking. Said he ran it and nothing was leaking. How could it have been leaking for me but not for him. Not sure what to think now. Any ideas?