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I have been trying to repair an 80hp 2001 four stroke Yamaha, but still have a problem.
The owner had everything serviced, and a new water pump installed at the beginning of the 2008 boating season. At that time she was having trouble keeping the battery charged, so the other shop installed a new battery. That battery still wouldn't stay charged, so the owner kept swapping out the battery with a fresh charged one before every use. The engine is on a 22' pontoon, and the owner doesn't have a trailer, so getting it worked on is more difficult. Around the end of the season the boat quit running, and this is when I got involved. I pulled the boat out and found a fried regulator, and a hole burned in the case of the CDI unit. Everything else looked and checked out fine, so I replaced the regulator, and CDI. The boat started and was charging the battery at 14.5 volts. After a short test run the over heat alarm sounded. The block was warm, but not hot enough burn you anywhere you could touch it. I started the engine back up, and the alarm sounded again, but the block wasn't hot enough to burn your hand, after a few minutes of running. I could unplug the temp sensor and stop the alarm, plug it back up and get the alarm again, and the waterpump is pumping a strong stream of water at 15psi.
I removed the sensor and checked it against the readings listed in the Yamaha manual. The readings were a little off, but close to what was listed, so I ordered a new sensor, and thermostat.
After installing the new sensor and thermostat, the engine started and the alarm went off while ideling tied to the dock. The engine had only been running for around a minute when the alarm started. I felt the block and it was warm, but not hot. I unplugged the new sensor and the alarm changed tones, the engine idle speed changed, but the alarm kept going off.
I then removed the new sensor and replaced it with the old one. I started the engine and didn't get an alarm until after the engine ran for about 5 minutes, but the block still didn't get hot enough to burn your hand. I could touch it anywhere for as long as I wanted to, without getting burned. I could unplug the old sensor and the alarm would stop.
When the new sensor was installed, once the alarm sounded, unplugging the sensor didn't stop the alarm, it only changed the tone.
I left the old sensor installed, and removed the thermostat. I ran the engine for around an hour with the thermostat removed and never got another alarm, but I still haven't fixed the problem.
I can't give the boat back to the customer until I found out the real problem, and without pulling the powerhead to check for blown gaskets etc.. I don't know where to look next. There aren't any external leaks, or signs of water in the oil. The engine doesn't skip, or have water on the plugs. Every cylinder pegged a 160lb compression guage.
Without throwing guesses into the air. does anyone have a clue? I have tested and, or, replaced everything the manual says will give an over temp alarm.
The owner had everything serviced, and a new water pump installed at the beginning of the 2008 boating season. At that time she was having trouble keeping the battery charged, so the other shop installed a new battery. That battery still wouldn't stay charged, so the owner kept swapping out the battery with a fresh charged one before every use. The engine is on a 22' pontoon, and the owner doesn't have a trailer, so getting it worked on is more difficult. Around the end of the season the boat quit running, and this is when I got involved. I pulled the boat out and found a fried regulator, and a hole burned in the case of the CDI unit. Everything else looked and checked out fine, so I replaced the regulator, and CDI. The boat started and was charging the battery at 14.5 volts. After a short test run the over heat alarm sounded. The block was warm, but not hot enough burn you anywhere you could touch it. I started the engine back up, and the alarm sounded again, but the block wasn't hot enough to burn your hand, after a few minutes of running. I could unplug the temp sensor and stop the alarm, plug it back up and get the alarm again, and the waterpump is pumping a strong stream of water at 15psi.
I removed the sensor and checked it against the readings listed in the Yamaha manual. The readings were a little off, but close to what was listed, so I ordered a new sensor, and thermostat.
After installing the new sensor and thermostat, the engine started and the alarm went off while ideling tied to the dock. The engine had only been running for around a minute when the alarm started. I felt the block and it was warm, but not hot. I unplugged the new sensor and the alarm changed tones, the engine idle speed changed, but the alarm kept going off.
I then removed the new sensor and replaced it with the old one. I started the engine and didn't get an alarm until after the engine ran for about 5 minutes, but the block still didn't get hot enough to burn your hand. I could touch it anywhere for as long as I wanted to, without getting burned. I could unplug the old sensor and the alarm would stop.
When the new sensor was installed, once the alarm sounded, unplugging the sensor didn't stop the alarm, it only changed the tone.
I left the old sensor installed, and removed the thermostat. I ran the engine for around an hour with the thermostat removed and never got another alarm, but I still haven't fixed the problem.
I can't give the boat back to the customer until I found out the real problem, and without pulling the powerhead to check for blown gaskets etc.. I don't know where to look next. There aren't any external leaks, or signs of water in the oil. The engine doesn't skip, or have water on the plugs. Every cylinder pegged a 160lb compression guage.
Without throwing guesses into the air. does anyone have a clue? I have tested and, or, replaced everything the manual says will give an over temp alarm.
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