90 hp Mercury overheating alarm - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  90 hp Mercury overheating alarm

search | FAQ | profile | register | author help

Author Topic:   90 hp Mercury overheating alarm

gbrooks posted 07-13-2005 07:32 PM ET (US)
I am getting an sporadic overheating alarm while running over 3,000 rpms with my 1987 Mercury 90hp outboard. When I stop the boat and idle for only 5 seconds or so, the alarm stops. Sometimes I can run all day an have no alarm. On other days it goes off every 2-3 minutes when cruising. The impeller was replaced by a professional mechanic. I replaced the thermostat. The head gets appropriately warm, but not hot. ( For example it doesn't steam water sprinkled on the head.) Also, the discharge water (from the water exhaust, not the tell tale stream) is warm, but not hot. The connnection from the sending unit is tight and free of corrosion. Any ideas on what else I can check? Any ideas a re welcome andf appreciated! gbrooks
Clark Roberts posted 07-14-2005 07:35 AM ET (US)
There are two audible alarms on your engine: a beep, beep, beep is the "low oil level" warning and a steady beeeep is the overheat alarm. Sounds like your engine is NOT overheating so the problem may be the "alarm module" or the heat sensor. Check with your mechanic and/or reference a maintenance manual. Happy Whalin'... Clark... Spurce Creek Navy
gbrooks posted 07-14-2005 02:43 PM ET (US)
Thanks for the reply. I can swap out the heat sensor. It looks like a few screws is all that holds it in the head. But, if the sensor is not the problem, is replacing an alrm module wihin a layman's scope of mechanical ability? It looks like a lot of stuff comes together in that module! How hard is replacing an alarm module? (My mechanic will tell me he is the only person in a four-state area who should even look at it.)
bill705 posted 07-14-2005 09:42 PM ET (US)
gbrooks:
I've got a 1991 100hp that had similar problems.
The magnet on the oil tank float had come loose and dropped to the bottom of the post. The alarm actually should have been on constantly but the reed switch on the bottom of the tank was bad and barely making contact. On top of all that the alarm module was also bad because when I would short out the low oil contact it would only beep once and stop. I replaced the module first and that took care of the low oil beep but I still had the intermittent beeps and clicks. I replaced the reed switch in the tank next and then had a continuous beep because of the loose magnet in the tank. Had to replace the tank to fix that. Not too big of a job for any of the three but have to bleed the oil line from the tank to the pump.
The oil lines on my engine were really brittle and broke without hardly touching them. Both from the oil tank to the oil pump and from the oil pump to the fuel pump.
If you do anything in the area of those oil lines make sure they didn't break. The new oil tank was an upgrade because it has some internal braces to keep it from sucking in like my old one used to do.
Good Luck
bill705

Dooley posted 06-10-2009 04:27 AM ET (US)
I have a 1999 90 hp ELPTO, serial #OG895277. I was running across the lake and the alarm sounded, both a constant and intermittent, hi temp and low oil. I shut it down but could find nothing wrong except the alarm. Got it home, dumped the oil and removed the oil tank. The magnet was stuck. I cleaned it up good, tested it by inverting the tank, the alarm quit, reinstalled it. Started the engine and now a constant alarm goes off. This is the hi temp alarm. Shut it down, checked everything, can find nothing wrong. Now the alarm sounds all the time, even with the engine not running if the key is on. Everyone, including the manual says it's the module. I went to the dealer and they couldn't find one in the book for this model. Called Mercury and the factory rep told me my model does not have an alarm module. Just the sending units and the ignition switch. The horn is in the ignition switch. He told me to replace the switch. I find it hard to believe the switch would cause this.
Has anyone else encountered this problem? How can you check this thing out. The book tells how to check out the system with an alarm module, and it doesn't have one. I looked and there is not one.
HerbertOle posted 08-12-2009 08:13 PM ET (US)
I also have a 1987 merc 90hp outboard with a similar problem.
The steady alarm came on and will not go off. The next morning, the alarm still goes off by just turning the key, even without starting the motor. Water is pumping thru like normal. A mechanic said that the thermostat may be stuck. He said it could also be a bad sensor. Anyone have a clue?
jimh posted 08-12-2009 08:45 PM ET (US)
Please note: this thread was dormant for four years before recently being revived.
In these simple WIRED-OR alarm systems, you can locate the cause of the alarm by disconnecting the various sensors and monitoring the aural alert sounder. When you disconnect the sensor that is causing the alarm, the aural alert sounder will go quiet. If you disconnect all the sensors and the aural alert continues to sound, the cause is either a short circuit in the alarm circuit wiring or a malfunction in the aural alert sounder itself.
Nevek posted 05-29-2013 03:06 PM ET (US)
Jim,
Hate to revive an old thread but how do I find out where all the overheat sensors are located?
jimh posted 05-30-2013 09:42 AM ET (US)
To locate an electrical sensor which is attached to an alarm system, follow the wires from the alarm system central unit. The wires will attache to all the sensors which are part of the system.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: 90 hp Mercury overheating alarm
gbrooks	posted 07-13-2005 07:32 PM ET (US) I am getting an sporadic overheating alarm while running over 3,000 rpms with my 1987 Mercury 90hp outboard. When I stop the boat and idle for only 5 seconds or so, the alarm stops. Sometimes I can run all day an have no alarm. On other days it goes off every 2-3 minutes when cruising. The impeller was replaced by a professional mechanic. I replaced the thermostat. The head gets appropriately warm, but not hot. ( For example it doesn't steam water sprinkled on the head.) Also, the discharge water (from the water exhaust, not the tell tale stream) is warm, but not hot. The connnection from the sending unit is tight and free of corrosion. Any ideas on what else I can check? Any ideas a re welcome andf appreciated! gbrooks
Clark Roberts	posted 07-14-2005 07:35 AM ET (US) There are two audible alarms on your engine: a beep, beep, beep is the "low oil level" warning and a steady beeeep is the overheat alarm. Sounds like your engine is NOT overheating so the problem may be the "alarm module" or the heat sensor. Check with your mechanic and/or reference a maintenance manual. Happy Whalin'... Clark... Spurce Creek Navy
gbrooks	posted 07-14-2005 02:43 PM ET (US) Thanks for the reply. I can swap out the heat sensor. It looks like a few screws is all that holds it in the head. But, if the sensor is not the problem, is replacing an alrm module wihin a layman's scope of mechanical ability? It looks like a lot of stuff comes together in that module! How hard is replacing an alarm module? (My mechanic will tell me he is the only person in a four-state area who should even look at it.)
bill705	posted 07-14-2005 09:42 PM ET (US) gbrooks: I've got a 1991 100hp that had similar problems. The magnet on the oil tank float had come loose and dropped to the bottom of the post. The alarm actually should have been on constantly but the reed switch on the bottom of the tank was bad and barely making contact. On top of all that the alarm module was also bad because when I would short out the low oil contact it would only beep once and stop. I replaced the module first and that took care of the low oil beep but I still had the intermittent beeps and clicks. I replaced the reed switch in the tank next and then had a continuous beep because of the loose magnet in the tank. Had to replace the tank to fix that. Not too big of a job for any of the three but have to bleed the oil line from the tank to the pump. The oil lines on my engine were really brittle and broke without hardly touching them. Both from the oil tank to the oil pump and from the oil pump to the fuel pump. If you do anything in the area of those oil lines make sure they didn't break. The new oil tank was an upgrade because it has some internal braces to keep it from sucking in like my old one used to do. Good Luck bill705
Dooley	posted 06-10-2009 04:27 AM ET (US) I have a 1999 90 hp ELPTO, serial #OG895277. I was running across the lake and the alarm sounded, both a constant and intermittent, hi temp and low oil. I shut it down but could find nothing wrong except the alarm. Got it home, dumped the oil and removed the oil tank. The magnet was stuck. I cleaned it up good, tested it by inverting the tank, the alarm quit, reinstalled it. Started the engine and now a constant alarm goes off. This is the hi temp alarm. Shut it down, checked everything, can find nothing wrong. Now the alarm sounds all the time, even with the engine not running if the key is on. Everyone, including the manual says it's the module. I went to the dealer and they couldn't find one in the book for this model. Called Mercury and the factory rep told me my model does not have an alarm module. Just the sending units and the ignition switch. The horn is in the ignition switch. He told me to replace the switch. I find it hard to believe the switch would cause this. Has anyone else encountered this problem? How can you check this thing out. The book tells how to check out the system with an alarm module, and it doesn't have one. I looked and there is not one.
HerbertOle	posted 08-12-2009 08:13 PM ET (US) I also have a 1987 merc 90hp outboard with a similar problem. The steady alarm came on and will not go off. The next morning, the alarm still goes off by just turning the key, even without starting the motor. Water is pumping thru like normal. A mechanic said that the thermostat may be stuck. He said it could also be a bad sensor. Anyone have a clue?
jimh	posted 08-12-2009 08:45 PM ET (US) Please note: this thread was dormant for four years before recently being revived. In these simple WIRED-OR alarm systems, you can locate the cause of the alarm by disconnecting the various sensors and monitoring the aural alert sounder. When you disconnect the sensor that is causing the alarm, the aural alert sounder will go quiet. If you disconnect all the sensors and the aural alert continues to sound, the cause is either a short circuit in the alarm circuit wiring or a malfunction in the aural alert sounder itself.
Nevek	posted 05-29-2013 03:06 PM ET (US) Jim, Hate to revive an old thread but how do I find out where all the overheat sensors are located?
jimh	posted 05-30-2013 09:42 AM ET (US) To locate an electrical sensor which is attached to an alarm system, follow the wires from the alarm system central unit. The wires will attache to all the sensors which are part of the system.