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Author Topic:   Mercury OptiMax Water-in-Fuel Alarm

Ltsimp posted 05-23-2015 02:03 PM ET (US)
Hello all. The Guardian engine monitoring system on my 2001 150hp OptiMax is flashing an alarm bell and fuel warning. There is no horn activation, but yet the horn functions on key turn. The manual says that this is a water-in-fuel alarm but also states that the horn should sound four times every two minutes. I have emptied and dried out the fuel water separator and yet the flashing bell and fuel symbol persist. It has not hampered performance at all. Has anyone experienced this before or have any suggestions as to a fix? I should also add that their was no water present in the fuel.
jimh posted 05-24-2015 07:25 AM ET (US)
In any alarm system which is signaling an alarm, there are three possible states that may have occurred:
--the alarm system and its sensors are functioning normally and there is an actual alarm condition;
--there is a failed sensor and it is signaling an alarm condition when there actually is none; or
--the sensors are all working properly but the main electronic system of the alarm has failed and it is signaling an alarm condition when there actually is none.
Since you seem confident that no water is in the fuel, we rule out the first situation. The second situation seems likely.
There must be some sort of sensor that is intended to detect the presence of water in the fuel. I am not familiar with the details of your Mercury engine's system, but the sensor could be something as simple as two electrodes that immerse in a reservoir of fuel and measure the resistance between the electrodes; the water would be detected because it would create a difference resistance than gasoline. The fault could be due to something as simple as the two electrodes being mechanically bent so they come in contact.
Locate the sensor and inspect it. Try to make an electrical measurement of the electrical signal being sent by the sensor. If the sensor has failed so it sends a persistent alarm signal, then you can remedy the problem by repairing or replacing the sensor. If the sensor is not persistently sending an alarm signal, then you can suspect the main electronic component of the alarm system as being the cause.
martyn1075 posted 05-24-2015 11:41 AM ET (US)
It I recall it wasn't all that uncommon for sensors in the Optimax especially the first models to occasionally prematurely sound off. Probably just a faulty sensor. Love and hate relationship with sensors. They can really ruin your day that's for sure. If its just the old sensor then it's a reasonable repair.
martyn1075 posted 05-24-2015 11:49 AM ET (US)
I had the same problem occasionally with the thermostats in my Optimax. The sound would flash and beep at me at idol but would go away. Since I didn't want to cause any damage in case I was overheating it I replaced the thermostats. Did some diagnostics on how hot the engine was running and it was perfectly fine. Worked for awhile but did it again at times.
msl posted 05-26-2015 09:48 AM ET (US)
I had [persistent alarms for water in the fuel] on and off for several years and could not figure out the [cause]; even two different mechanics could not. Finally took it to a new mechanic. He went through the entire wiring harness and found two bad wires that were shorting and causing the alarm to go on and off. Had nothing to do with the sensors just a bad spot in the harness. We have twin 1999 Mercury 150 OptiMax engines.
jimh posted 05-26-2015 10:42 AM ET (US)
MSL--Thanks for that report on the chronic occurrence of a persistent false alarm for water in the fuel of your Mercury OptiMax outboard engine being caused by a short in the alarm wiring circuit. That is very useful information for investigation of the cause of a persistent false alarm in the water-in-fuel alarm circuit in Mercury OptiMax engines. Perhaps LT' can check the wiring on his Mercury OptiMax outboard to see if there is a wiring problem that is causing the water-in-fuel alarm.
Ltsimp posted 05-26-2015 02:59 PM ET (US)
Thank you for all the advice. I found all of it very useful in my troubleshooting. As there was never any horn activation I was stumped and the owners manual was of little help. I finally downloaded the latest manual from the manufacturers site and was surprised to find quite a few more pages than was in my original manual. This downloaded manual solved the problem for me. I had programmed in the 54 gallon fuel tank when I should have left it at zero. The alarm was telling me I was extremely low on fuel.
jimh posted 05-27-2015 12:38 AM ET (US)
I am surprised that the engine has an alarm for low fuel tank level. Usually that sort of alarm comes from an accessory gauge.

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Author	Topic: Mercury OptiMax Water-in-Fuel Alarm
Ltsimp	posted 05-23-2015 02:03 PM ET (US) Hello all. The Guardian engine monitoring system on my 2001 150hp OptiMax is flashing an alarm bell and fuel warning. There is no horn activation, but yet the horn functions on key turn. The manual says that this is a water-in-fuel alarm but also states that the horn should sound four times every two minutes. I have emptied and dried out the fuel water separator and yet the flashing bell and fuel symbol persist. It has not hampered performance at all. Has anyone experienced this before or have any suggestions as to a fix? I should also add that their was no water present in the fuel.
jimh	posted 05-24-2015 07:25 AM ET (US) In any alarm system which is signaling an alarm, there are three possible states that may have occurred: --the alarm system and its sensors are functioning normally and there is an actual alarm condition; --there is a failed sensor and it is signaling an alarm condition when there actually is none; or --the sensors are all working properly but the main electronic system of the alarm has failed and it is signaling an alarm condition when there actually is none. Since you seem confident that no water is in the fuel, we rule out the first situation. The second situation seems likely. There must be some sort of sensor that is intended to detect the presence of water in the fuel. I am not familiar with the details of your Mercury engine's system, but the sensor could be something as simple as two electrodes that immerse in a reservoir of fuel and measure the resistance between the electrodes; the water would be detected because it would create a difference resistance than gasoline. The fault could be due to something as simple as the two electrodes being mechanically bent so they come in contact. Locate the sensor and inspect it. Try to make an electrical measurement of the electrical signal being sent by the sensor. If the sensor has failed so it sends a persistent alarm signal, then you can remedy the problem by repairing or replacing the sensor. If the sensor is not persistently sending an alarm signal, then you can suspect the main electronic component of the alarm system as being the cause.
martyn1075	posted 05-24-2015 11:41 AM ET (US) It I recall it wasn't all that uncommon for sensors in the Optimax especially the first models to occasionally prematurely sound off. Probably just a faulty sensor. Love and hate relationship with sensors. They can really ruin your day that's for sure. If its just the old sensor then it's a reasonable repair.
martyn1075	posted 05-24-2015 11:49 AM ET (US) I had the same problem occasionally with the thermostats in my Optimax. The sound would flash and beep at me at idol but would go away. Since I didn't want to cause any damage in case I was overheating it I replaced the thermostats. Did some diagnostics on how hot the engine was running and it was perfectly fine. Worked for awhile but did it again at times.
msl	posted 05-26-2015 09:48 AM ET (US) I had [persistent alarms for water in the fuel] on and off for several years and could not figure out the [cause]; even two different mechanics could not. Finally took it to a new mechanic. He went through the entire wiring harness and found two bad wires that were shorting and causing the alarm to go on and off. Had nothing to do with the sensors just a bad spot in the harness. We have twin 1999 Mercury 150 OptiMax engines.
jimh	posted 05-26-2015 10:42 AM ET (US) MSL--Thanks for that report on the chronic occurrence of a persistent false alarm for water in the fuel of your Mercury OptiMax outboard engine being caused by a short in the alarm wiring circuit. That is very useful information for investigation of the cause of a persistent false alarm in the water-in-fuel alarm circuit in Mercury OptiMax engines. Perhaps LT' can check the wiring on his Mercury OptiMax outboard to see if there is a wiring problem that is causing the water-in-fuel alarm.
Ltsimp	posted 05-26-2015 02:59 PM ET (US) Thank you for all the advice. I found all of it very useful in my troubleshooting. As there was never any horn activation I was stumped and the owners manual was of little help. I finally downloaded the latest manual from the manufacturers site and was surprised to find quite a few more pages than was in my original manual. This downloaded manual solved the problem for me. I had programmed in the 54 gallon fuel tank when I should have left it at zero. The alarm was telling me I was extremely low on fuel.
jimh	posted 05-27-2015 12:38 AM ET (US) I am surprised that the engine has an alarm for low fuel tank level. Usually that sort of alarm comes from an accessory gauge.