Mercury 175 EFI Beeeeeep

[adriandavidpayne]

I have a 1999 Mercury 175 EFI. If I launch the boat and take off it runs like a scalded dog at over 70mph for miles with no Beeps. If I cruise for just a couple of minutes at very low speed I will get a High Heat warning Beeeeeeep. My water pressure is about 4 at idle and 10 or 12 at WOT.
What does the fact that it does not beep at all during WOT tell me? This thing barley Pees unless it's revved up also. BTW, the impeller was changed in September with 5 trips on it. Thanks.

 

[sullmate]

could be the poppet valve needs replacing

 

[CharlieB]

Check ignition timing. Then disconnect the throttle cable (motor NOT running) move the throttle arm to WOT and back while watching the timing lever. Look to make sure the timing lever moves smoothly and is not sticking anywhere which could allow retarded timing while at partial throttle.

T-stats could be bad, WOT running engine temp is controlled by the poppet valve so the stats aren't really doing anything. Low speed running the stats do everything, a bad stat can then cause an overheat.

Remove both T-stats, place them in a pan of water with a thermometer. heat until they begin to open. What temp do they fully open?

 

[adriandavidpayne]

*Update. It was the Bad Thermostat causing the problems. Life is Good!