Mercury 60hp 4 stroke warning alarm.

I have a 60hp Merc, 4 stroke tiller on my boat. It's a 2001, yep 20 years old and still runs great. The last few times out while trolling I have been getting a continuous warning signal about every 20 minutes or so. I kick it in and out of gear and it doesn't make much diferance, but in a few minutes the alarm goes off. The water coming out has a strong stream and when I feel it it's not very hot. Motor oil was changed and the level is dead center on the dip stick?? 

Motor idles real smooth even a 1 MPH, takes right off when I throttle up.  Been doing some searching and no real answers, any help out there would be really appreciated.

Water pump impellers should be change every 2 to 3 years to keep the motor from runnig hot even tho it looks like there is plenty water coming out.

Check eyesman’s attachment below.  It gives good insight on Merc alarms.  Was interesting that a low battery can set off the alarm.  

Polski,

I had a similar issue a number of years back.

Decent stream of water coming out, but would get an alarm if idling too long or operating at WOT.  Wasn’t sure what the alarm was, and the oil reservoir was full. 

To verify, I took off the motor cover, went for a ride, and shot the cylinder head with an infrared thermometer.  I was able to verify that I was running too hot.

First thing I did was remove the thermostats, and put them in a pan of water on the oven burner on low, with a thermometer in the water. I was able to visually verify that they opened up at the right temperature, so I replaced the water pump, and that took care of the alarm. 

So after a bunch of You Tube videos and talking to my local Merc dealer they suggested changing the impeller. It's still the orignal and although still pumping may not be putting the volume through that I need when trolling at idle speeds.  

So I drop the lower unit and take the old impeller and housing to the dealer.  I know I could order one on line but I want it today and a few bucks extra so what. The dealer looks it up, brings out 3 options from just the impeller, to one with gaskets and one with everything including the housing. OK, except when I look at the impeller and it's clearly bigger than my old one. The deal then opens the packages and none of the gaskets match my housing??

After about 45 minutes of trying out different impellers we find one that matches. They told me it was for a Sea Pro model, which is intended for commercial use?  OK yet my serial and model number don't indicate it's anything but the standard model? I'm the original owner so  know nothing was changed to a different lower unit over the years.

So I buy it and will put it in.  I've sent an email to Mercury with the above info, not really expecting any clarification but we'll see.

I've actually had the alarm itself go bad it always would beep when you I'd turn the key on which was normal then it then it started going off randomly and eventually stayed on continously while the key was on even though there was nothing wrong with the motor ran great and pumped cool water 

The sensor was something I thought about too just because it seems to be cooling fine, will for sure take it to a mechanic as needed, just like to have some ideal beforehand. 

I use Seafoam with every fillup and have for a long time, thanks for the comments, I'll post more info as I have it.

Run some Sea Foam then take it a mechanic that will work on older motors.  Some of the dealers won't.

It's 20 years old

It's time to take a look under the hood with a mechanic

It could be something simple as a bad sensor

Try putting some sea foam in your gas and run that through for awhile, it worked for my brothers boat...no more beep.

Explore this website, it may give an answer.