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Author Topic:   Desperate for Help with Mercury

bboeri posted 07-25-2012 06:40 PM ET (US)
Hello All. I have two boats, one a Whaler Montauk and the other a pontoon boat that I use as a work platform for my oyster farm. That boat has a 2002 Mercury Bigfoot 60-HP FOURSTROKLE EFI on it. It has been giving me fits for months now. It is an intermittent problem that gets worse as time goes on. In the morning, I bring the boat up to about 4,000-RPM and after about ten minutes the warning horn goes off. I throttle down to idle and the horn ceases. I then can get it up to about 3,000-RPM before the horn sounds again. Throttle down to idle, the horn goes off. Throttle up to 2,000-RPM, after five minutes the horn sounds again. I throttle down to idle and the horn shuts down. I can then barely limp along at 1,500-RPM the rest of the day, but above that, the horn sounds.
I have had four mechanics look at this. I replaced the water pump impeller three times with no change. Replaced the thermostat and thermostat cover with no change. If you can believe this, removed the power head to check all cooling passages both in the motor and in the lower unit. All clear and no change. Checked the cylinders for warped and cracked heads. All pressure held. No evidence of warping. The mechanic put a computer to the motor, which indicated that the motor was overheating, but no evidence of this except for the horn and it going into Guardian mode. We then changed the temperature sensor, and viola! No problem for three months. Now it is happening all over again. Exact same conditions. What should I do that I haven't already done--except burn the damn thing? Any help would be greatly appreciated. This is costing me valuable time and money on the farm.
Bob
Jefecinco posted 07-25-2012 07:00 PM ET (US)
Bob--You've covered all the overheating faults I can think of. Is the problem possibly electronic? Possibly a false alarm caused by another defective sensor? I wouldn't think that's too likely but if it's happened once it could happen again.
Butch
jimh posted 07-25-2012 08:16 PM ET (US)
Is there a way to interpret the meaning of the aural alarm? Is there a way to tell when the alarm sounds what the alarm is warning about? Often you see that several sensors are connected in a WIRED-OR arrangement so that if any of them signal an alarm the sounder is activated. If that is true for your Mercury outboard engine, perhaps you can determine which sensor is causing the alarm by the following method:
--wait for the alarm to sound;
--while the alarm is sounding, disconnect the individual sensors of the alarm circuit, one at a time;
--if the alarm is silenced when a particular sensor is disconnected, that sensor is likely to be the cause of the alarm.
With this method you can identify the sensor that is signaling the alarm condition. Once you have the sensor identified, you can remove the sensor and test if on the bench to see if its performance is within specification.
martyn1075 posted 07-27-2012 12:39 AM ET (US)
I agree I would heavily investigate the sensor or sensors. It sounds exactly what a wacky sensor would do. The Smartcraft meter has no choice but to sound and show an error if the sensor throws it off and reads beyond what the engine computer has given a limit for.
Perhaps rent or purchase a heat gun and actually aim it at the engine with the cover off and read the temp. I might try that if I were you as soon as this alarm goes off. The might help you determine if your engine is truly overheating or in fact it is a sensor that has gone mad.
It might even be a lose wire in and around the sensor or Smart Craft sender unit. The word sensor is appropriate as it is derived from sensitive and these mercury sensors are truly that sensitive.
Martyn
swist posted 07-27-2012 08:46 AM ET (US)
I don't find it so unlikely that the temp sensor died again. I had a 1993 Yamaha 225 where the throttle position sensor died three times in the 11 years I owned it (each time triggering a different set of weird performance problems). And I too spent a lot of time assuming it had to be something else.
jfortson posted 07-27-2012 10:27 AM ET (US)
From your post you have already spent a lot of time and expense on this. Adding a temp gauge would help determine if the motor is actually overheating - that $40 to $60. You could possibly mount the sensor close to the factory sensor so you are reading the same area. Or possibly one of the infared temp readers, but I do not know much about them.
That should help answer the question if it is actually overheating or if the problem is with the sensor.
vin1722or posted 07-28-2012 01:31 PM ET (US)
It sounds like a bad sensor,we have many mercs in our marina and sensors are a problem with most.As for yamaha sensors.We have had only a few go bad and mostly with older engines.
bboeri posted 08-16-2012 06:36 PM ET (US)
Thanks for all the suggestions guys, I always appreciate the help I get on the forum. You may not believe this, but it turned out that a little bitty piece of a previous temperature sensor had broken off and was wedged in a very difficult to get at section of the cooling water channel. Once it was finally removed, the engine runs like a champ. And it only cost me another $450 to find it! Should have sent my son to marine mechanic school instead of college for a degree in marine biology....
Thanks again.
PeteB88 posted 08-16-2012 09:44 PM ET (US)
All families with boats should have relative who went to marine mechanics school. Maybe I'll go to marine mechanics school. what the hell.
jimh posted 08-16-2012 10:23 PM ET (US)
Thank you for giving us the outcome of the repair and the resolution of the problem. Readers appreciate this information.

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Author	Topic: Desperate for Help with Mercury
bboeri	posted 07-25-2012 06:40 PM ET (US) Hello All. I have two boats, one a Whaler Montauk and the other a pontoon boat that I use as a work platform for my oyster farm. That boat has a 2002 Mercury Bigfoot 60-HP FOURSTROKLE EFI on it. It has been giving me fits for months now. It is an intermittent problem that gets worse as time goes on. In the morning, I bring the boat up to about 4,000-RPM and after about ten minutes the warning horn goes off. I throttle down to idle and the horn ceases. I then can get it up to about 3,000-RPM before the horn sounds again. Throttle down to idle, the horn goes off. Throttle up to 2,000-RPM, after five minutes the horn sounds again. I throttle down to idle and the horn shuts down. I can then barely limp along at 1,500-RPM the rest of the day, but above that, the horn sounds. I have had four mechanics look at this. I replaced the water pump impeller three times with no change. Replaced the thermostat and thermostat cover with no change. If you can believe this, removed the power head to check all cooling passages both in the motor and in the lower unit. All clear and no change. Checked the cylinders for warped and cracked heads. All pressure held. No evidence of warping. The mechanic put a computer to the motor, which indicated that the motor was overheating, but no evidence of this except for the horn and it going into Guardian mode. We then changed the temperature sensor, and viola! No problem for three months. Now it is happening all over again. Exact same conditions. What should I do that I haven't already done--except burn the damn thing? Any help would be greatly appreciated. This is costing me valuable time and money on the farm. Bob
Jefecinco	posted 07-25-2012 07:00 PM ET (US) Bob--You've covered all the overheating faults I can think of. Is the problem possibly electronic? Possibly a false alarm caused by another defective sensor? I wouldn't think that's too likely but if it's happened once it could happen again. Butch
jimh	posted 07-25-2012 08:16 PM ET (US) Is there a way to interpret the meaning of the aural alarm? Is there a way to tell when the alarm sounds what the alarm is warning about? Often you see that several sensors are connected in a WIRED-OR arrangement so that if any of them signal an alarm the sounder is activated. If that is true for your Mercury outboard engine, perhaps you can determine which sensor is causing the alarm by the following method: --wait for the alarm to sound; --while the alarm is sounding, disconnect the individual sensors of the alarm circuit, one at a time; --if the alarm is silenced when a particular sensor is disconnected, that sensor is likely to be the cause of the alarm. With this method you can identify the sensor that is signaling the alarm condition. Once you have the sensor identified, you can remove the sensor and test if on the bench to see if its performance is within specification.
martyn1075	posted 07-27-2012 12:39 AM ET (US) I agree I would heavily investigate the sensor or sensors. It sounds exactly what a wacky sensor would do. The Smartcraft meter has no choice but to sound and show an error if the sensor throws it off and reads beyond what the engine computer has given a limit for. Perhaps rent or purchase a heat gun and actually aim it at the engine with the cover off and read the temp. I might try that if I were you as soon as this alarm goes off. The might help you determine if your engine is truly overheating or in fact it is a sensor that has gone mad. It might even be a lose wire in and around the sensor or Smart Craft sender unit. The word sensor is appropriate as it is derived from sensitive and these mercury sensors are truly that sensitive. Martyn
swist	posted 07-27-2012 08:46 AM ET (US) I don't find it so unlikely that the temp sensor died again. I had a 1993 Yamaha 225 where the throttle position sensor died three times in the 11 years I owned it (each time triggering a different set of weird performance problems). And I too spent a lot of time assuming it had to be something else.
jfortson	posted 07-27-2012 10:27 AM ET (US) From your post you have already spent a lot of time and expense on this. Adding a temp gauge would help determine if the motor is actually overheating - that $40 to $60. You could possibly mount the sensor close to the factory sensor so you are reading the same area. Or possibly one of the infared temp readers, but I do not know much about them. That should help answer the question if it is actually overheating or if the problem is with the sensor.
vin1722or	posted 07-28-2012 01:31 PM ET (US) It sounds like a bad sensor,we have many mercs in our marina and sensors are a problem with most.As for yamaha sensors.We have had only a few go bad and mostly with older engines.
bboeri	posted 08-16-2012 06:36 PM ET (US) Thanks for all the suggestions guys, I always appreciate the help I get on the forum. You may not believe this, but it turned out that a little bitty piece of a previous temperature sensor had broken off and was wedged in a very difficult to get at section of the cooling water channel. Once it was finally removed, the engine runs like a champ. And it only cost me another $450 to find it! Should have sent my son to marine mechanic school instead of college for a degree in marine biology.... Thanks again.
PeteB88	posted 08-16-2012 09:44 PM ET (US) All families with boats should have relative who went to marine mechanics school. Maybe I'll go to marine mechanics school. what the hell.
jimh	posted 08-16-2012 10:23 PM ET (US) Thank you for giving us the outcome of the repair and the resolution of the problem. Readers appreciate this information.