1991 100 HP Merc sensor beeps

[Paulbasstracker]

Can someone give me some input on this problem, I have a 1991 Mercury outboard that the overheat and low oil sensor starts to beep after you have been trolling for awhile. It will start out real faint sounding like it is shorting out and then stay on continually even if you shut the motor off and let it sit for a while. It sat all night one time and did the same alarm after it started in the morning, so I know that the motor was not overheating. There is plenty of oil and the water is coming out the back of the motor so it is going through the cooling system. I was wondering if it was a bad sensor or something more than that? If so are the sensors something you can replace or will it need to go to a shop?

 

[electricjohn]

Re: 1991 100 HP Merc sensor beeps

Each of the sensors, actually switches, ground the horn in your throttle (thereby completeing the circuit) if there is a problem. You can disconnect each switch individually at the motor on the starboard side to isolate which switch is going to ground on you. There should be a plastic terminal with 3 (I think) tan wires on it. One wire comes from the horn, one goes to the low oil switch, and the other goes to the overheat switch in the block. The low oil switch is built into the oil tank and cannot be replaced. You must replace the whole tank, about $40.

If your horn was beeping after the key was turned off, you have other problems too, because the key is what powers up the alarm circuit inside the throttle.

edit; Let me add that the oil level float in the oil tank does lose its bouyancy after about 15 years. It could be as simple as that.

 

[Nauset #37766]

Re: 1991 100 HP Merc sensor beeps

I've got the same engine and had the same problem.
I shorted the leads from the oil switch and would only have one beep, not the beep beep beep that it should have.

I replaced the control module and then had the correct indication when the leads were shorted but still had the horn chirping and beeping at different levels.

I then replaced the reed switch on the bottom of the tank which is an easy job because only one screw holds it into a blind hole. No oil will come out when it is removed. I then had a steady beep, beep, beep when the key was turned on.

Had to replace the tank because the ring magnet on the bottom of the float in the tank had came loose. no way to fix it except replace the tank.

The reed switch had a high resistance when it should have had continuity and that was the reason for the chirping and wierd sounds

Bill

 

[PISTONESAL]

Re: 1991 100 HP Merc sensor beeps

Hello,

I have a Mercury Elpto that gives me a constant beeeeepp. I disconnected the oil tank and it went away. The switch and oil tank are seperate part numbers. Can I just replace the switch in the tank? Please advice.

Thanks

 

[Nauset #37766]

Re: 1991 100 HP Merc sensor beeps

Yes it's an easy job, only one screw holds it into a blind hole on the bottom.
Before you buy a new switch though, just drop it down out of the hole (no oil is going to come out) and see if it still beeps. If it stops beeping when you drop it down, it's the magnet on the bottom of the float inside the tank that has come loose or the float is stuck. I don't really see how the float can stick unless it has set without oil in the tank and has sort of gummed up. If the magnet has come loose the fix for that is a new tank which is a fairly easy job also.
Bill

 

[PISTONESAL]

Re: 1991 100 HP Merc sensor beeps

Nassett,

Thanks for the response. I really appreciate it. Will do it.

Thanks again

Sal