2004 Mercury EFI 150hp alarm and noticing water stream is very hot

RuddsRetreat

My 2004 Mercury efi 150 hp 2 stroke seems to have a slight problem with alarm going off.  when alarm sounds, its a continuous sound.  I drop into neutral than it goes off.  It happens a 3 to 4 times during the day on the water.  My pee stream is good, engine sounds good, however my friend put his hand down to feel the pee stream and noticed that is very hot.  Like I said everything seems ok with the exception of alarm going off.  Even putting my hand on engine cover is not blazing hot, although black engine and hot sun makes a hot cover.   Can anyone tell me if the pee stream should be very hot, is it ok to be very hot or should I be concerned?  

Ernest_T

The overflow can be pretty hot.  Generally it is cooler at idle and gets hotter as the rpms increase.  I think the specs call for a temperature less than 130 degrees on my Yamaha 4 stroke at idle and all the way up to 250 or so at higher rpms.  120 degrees would be pretty hot to the touch but still within specs at idle.

Regardless of how hot the overflow feels, if the alarm is going off then you probably have an overheat issue.  I'd say the most likely problem would be with the impeller pump, or some blockage in the intake.  You may be getting water flow through the system, just not at a high enough rate of flow.  When is the last time the water pump was serviced and the impeller changed?  It could be a pretty simple fix.

RuddsRetreat

Ernest I just bought boat from a gentleman who is a mechanic and took care of boat since new.  He said waterpump was replace last year.  I had on water yesturday and alarm only came on 1 time at beginning when bow was up.  I noticed that and try to keep it trimmed so bow doesnt go up as high.  It seemed to work,  Can it be that trimming engine up might be causing not enough water flow which could be setting alarm?  The stream is hot but it ran 30 mph with 6 people on board not problem for 2 hours giving it a brake between hours.  MY boat is Hurricane GS 211.  When I flush out with muffs on the stream takes about 30 seconds to start but it looks as if water is so hot that it steams alittle.

Ernest_T

Another thought is a bad thermostat.  I know that many mechanics recommend replacing them whenever the water pump is serviced.  The thermostat may not be opening fully, be corroded, etc..  It is not unusual for it to take a few seconds for the water to start flowing.  The thermostat is supposed to stay closed until the engine warms a little, so I'm thinking the thermostat is working, but maybe not completely.  I don't know enough about your engine model to make any other guesses.  A dealer may be able to hook it up to a diagnostic system, and tell you pretty quick if there is a problem or not.

RuddsRetreat

I just dropped off at mechanic and he also thinks thermostat,  so I will update with result.