Another Alarm question.

[HOGEYE]

A friend has a 2002 Mercury 50 hp 4stroke. Once he gets up and going the constant alarm sounds and the engine bogs down. Once he idles down the alarm goes off and it runs normal again. He replaced the water impeller already. The guy he bought it from put a 12 ptich prop on it to make it troll slower also. Any ideas what could be wrong?

[musky hunter]

It has overheating symptoms. There may be a plugged inlet or something other than the impeller preventing proper cooling. Before going further, verify that it indeed squirts a strong water stream out, and the stream should be warm to the touch to prove that proper cooling is happening. There are other things that might cause the symptom, but I burned up a motor as it bogged down on full throttle, I didn't even realize what was happening until it was too late.

[Valv]

It could be your prop is too small (pitch) and max rpm governor kicks in. It might troll slower but you have to check your rpms. Do you have a tach ?

[hoggs222]

My lund w/115 Yamaha did the same thing. It was an oil sensor. Slow speeds were fine and once you started going fast, the alarm would come on and would start bogging down/ shaking the motor. We were about 8 miles from the boat landing on Mille Lacs and had to go about 2mph to shore!

[marine_man]

It definately sounds like the motor is going into the "limp home" mode and cuts the power to prevent damage to the engine... could be oil or temperature induced...

marine_man