Logo
FULL SITE MENU

Overheat Alarm

P

psekul

New member
Hello,

I am a new owner of a 1999 90 HP Mercury ELTPO. Yesterday, the temp warning buzzer (constant horn) went off. Got towed back to ramp. This morning I turned ignition to on and the buzzer sounded. Obviously, the engine is not overheating, since it had not been run for many hours. I disconnected the brown wire going to sending unit and buzzer continued.

Based on my research, this would indicate a bad ground wire (please correct me if this is wrong). If this is the case, where would the ground wire be located. There are three grounds on the engine and they look to be in excellent condition. I looked under helm but cannot identify the right one.

Also of note - when the motor is running, I can slightly back off the key at which time the instrument panel stops working, but the buzzer quits, while the engine still runs. I assume this would be something that is not associated with the buzzer problem and just a function of a 17 year old ignition switch. But I thought I would mention.

BTW - the remote control is the console mount type with a separately mounted ignition switch and emergency shut off toggle switch.

So what steps should I take to find fix for problem? Thanks for your help.
 
Sound like bad contacts in ignition switch,Usually test for alarm buzzer is to ground brown wire.Is engine overheating? Is telltale flowing strong,Is water flow too hot to hold hand in? Can hand be placed on head for a six second count without scorching fingers? An infrared thermo gun comes in handy here! The sensor uses the engine block as ground,only 1 wire goes to it. Keep us posted
 
johnnygjr said:
Sound like bad contacts in ignition switch,Usually test for alarm buzzer is to ground brown wire.Is engine overheating? Is telltale flowing strong,Is water flow too hot to hold hand in? Can hand be placed on head for a six second count without scorching fingers? An infrared thermo gun comes in handy here! The sensor uses the engine block as ground,only 1 wire goes to it. Keep us posted
Click to expand...


Thanks Johnny,

Yesterday, when the alarm first sounded, the engine was not hot to touch. Combined with the fact that the alarm sounded this morning, when the engine had not been run leads me to believe it is not over heating. The tell tale is pumping strong. I found an online service manual that says to replace the warning controller if the horn still sounds when sending unit is disconnected. Looks like a $60 part. I hope I am not chasing my tail, but chasing down a bad ground isn't going to work for me.

There are many posts on different forums where there is no follow-up. Seems like a common problem for this engine. I will definitely post outcome so others can know the solution that worked for me.
 
Mercury temp sensors are a pretty basic piece of kit.

They are simple resistance sensor - if they heat up past a pre-determined temp they "go to ground" (allowing the current to pass) which completes the horn circuit and "beeeeeeep".

They are known to fail - it's not really a manufacturing flaw, they are just a component with a limited lifespan.

A second common issue that causes a warning horn exists on 2 stroke oil injected motors that have the low oil sensor that includes the magnetic float in the oil tank. The magnet/float busts, the magnet goes to the bottom of the tank activating the low oil sensor and "beeeeeep".

In neither case is there an "actual issue", being overheat or lack of oil.

In both cases you can by-pass the "false alarm" by simply disconnecting the lead(s) to the sensor in question. But if you do you leave yourself "unprotected" should an actual issue occur.

Personally I would leave an oil sensor disconnected since it only relates to "oil level" and not whether the injection system is working or not. But in the case of the temp sensor, I would replace that at earliest convenience since an overheat can be caused by a few different issues and can do a lot of damage in fairly short order.

Not that lack of oil won't toast things, but again, just a "oil level" sensor and if you top up before each outing you are unlikely to ever run out of oil...
 
galamb said:
Mercury temp sensors are a pretty basic piece of kit.

They are simple resistance sensor - if they heat up past a pre-determined temp they "go to ground" (allowing the current to pass) which completes the horn circuit and "beeeeeeep".

They are known to fail - it's not really a manufacturing flaw, they are just a component with a limited lifespan.

A second common issue that causes a warning horn exists on 2 stroke oil injected motors that have the low oil sensor that includes the magnetic float in the oil tank. The magnet/float busts, the magnet goes to the bottom of the tank activating the low oil sensor and "beeeeeep".

In neither case is there an "actual issue", being overheat or lack of oil.

In both cases you can by-pass the "false alarm" by simply disconnecting the lead(s) to the sensor in question. But if you do you leave yourself "unprotected" should an actual issue occur.

Personally I would leave an oil sensor disconnected since it only relates to "oil level" and not whether the injection system is working or not. But in the case of the temp sensor, I would replace that at earliest convenience since an overheat can be caused by a few different issues and can do a lot of damage in fairly short order.

Not that lack of oil won't toast things, but again, just a "oil level" sensor and if you top up before each outing you are unlikely to ever run out of oil...
Click to expand...

Thanks Graham,

I have seen a lot of suggestions in other forums stating that the oil sensor causes the false alarm. I wonder if the false alarm you and others are referring to is the constant beep. My understanding is that the constant tone is the overheat alarm and that is what I have been focusing on. In your experience, could the oil sensor create a solid warning, rather than the intermittent beep?

I agree that the low oil sensor is not as critical as the overheat sensor, especially on my boat which has a small fuel tank. I get at least two fill-ups per gallon of oil. So if I top it off at fuel fill-up, I will never have a low oil issue. If the oil sensor is the cause of the problem, I would disconnect it without a problem. Just wondering. Thanks again.
 
Merc has a few different versions of it's "guardian" that alarms when you have a problem.

The more complex versions have a long uninterrupted beep for over heat, and different numbers of beeps or "patterns" to identify various other issues (everything from water in the fuel to a engine computer or sensor problem).

On older, carburated, 2 stroke models in particular you get a "horn" - overheats - beeeeeeep - run out of oil - beeeeeeep - super basic alarm that tells you that you have one of two issues and no extra info derived from the alarm itself.

So depending on exactly what model you have and how complicated the guardian is on your motor. If you have a carburated 2 stroke (so no engine computer, no sensors, injectors etc etc) you would only get the beeeeeeep when there is an issue....
 
I wanted to post the resolution to my problem in hopes it could help others in future.

Graham, you were right on, but I really wanted to verify what guardian package I have. I called the Mercury tech support line with my serial number and they gave me the low down on the warning system and the wiring colors as well.

My problem was the low oil sensor, which I do not need, so I left the wire disconnected.

They also informed me that if the horn did not stop, I would be looking at new warning senor module or a short somewhere in the harness. Thank goodness it wasn't a short.

For anyone with this issue, find out what warning sensors you have, the wiring colors and the beep cadence for each warning. Then you can start narrowing things down.

Anyway, problem solved. Thanks for all replies.
 
Back
Top