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Yamaha 50hp 4 stroke Outboard FT50 overheating problem solved
I write this in the hope that it will help others avoid the excessive time and energy trying to solve this problem.
The engine is 7 years old and began to have overheating problems. The symptoms were that all was normal while the engine was working hard. As we approached a dock and began to slow down or after a few secs at tickover the overheat warning alarm would sound.
I was fairly sure that the problem was a bad impellor so I dropped the foot and investigated. The impellor looked perfect but I replaced it anyway. Re-assemble the engine and tried again. No improvement !. I thought it might be a thermostat problem but I removed it checked it in a saucepan of water and it seemed to work well. I tried the engine again with no thermostat installed still no change. I thought it might be the temperature sensor at fault so I removed it tested it in a saucepan with water being heated and it was within specs.
I took of the foot again and attached a garden hose to the bottom of the water tube as it protrudes through the centre mid section of the engine. When water pressure was applied a good stream of water came through the ‘pisser’.
I put the foot in a bath of water and connected an electric drill to the drive shaft and rotated it with the drill and water was being pumped out of the water pump from the hole where the water tube would connect. I was however unsure that the pressure there was good enough since when I blocked the hole with my thumb it was fairly easy to block the stream and when I did this water escaped from the water pump housing from the gap that surrounds the drive shaft. This made me buy a brand new replacement water pump with another impellor and all the other water pump components including the housing.
Installed it ran the engine again no improvement. I begin to doubt my sanity !
There must be some serious internal problems so remove the engine from the boat. Remove the power head, pan, engine sump and inspect. First problem water tube which carries water from the pump up to the power head is badly corroded. Attempted a soldered repair of this copper pipe because a replacement was not easy to obtain or easy to fit. Reassembled the engine and installed on the boat .
No improvement UGH ! What is going on here ? Time to buy a new engine !!
Took the engine off again and another complete strip down of the power head, pan, engine sump and exhaust chamber and inspect again. There are many chambers in the engine sump to power head joint and I was unclear about which chambers carried the water so I use a compressed air gun from the water tube and felt for drafts at the joint this revealed which chamber brought the water to the power head.
A compressed air gun upwards into the power head at this chamber should reveal a draft somewhere eg the pisser tube or the thermostat but I could feel nothing. So there is a blockage in the power head somewhere but where ?
Looking at the port side of the engine you see a long aluminium manifold that runs from top to bottom of the power head its called the outer cover exhaust. At the top of it is the opening for the thermostat. I removed this cover to inspect. Inside I found a pristine looking manifold except for a pile of debris at the bottom of the casting. Poking around with a screwdriver I removed some light crud and then began to see the object was moving when I touched it. A bit more prodding and a pair of needle nose pliers allowed me remove a piece of crud about the size of a cigarette butt. I had no idea what it was but is was clearly blocking an important water passage.
Cleaned the passage reassembled the engine put it back on the boat everything works well. Problem solved !
I took the piece of crud to a local gathering at showed it around. A friend George Hemming recognized it immediately. It was the remains of a pencil anode installed on a brass plug in the engine water system.
The lead anode had corroded near the point where it screws into the brass plug and the remaining piece had fallen into the water chamber eventually completely blocking a hole in the water circulation system.
Many hours of work and a great deal of anxiety caused by this problem. I should have been more careful when I saw a perfect impellor ! I should have given this a great deal more thought.
I hope this tale helps someone. Incidently no mention of this anode in the engine parts book or in the service instructions. Just a brass plug is shown in the parts book. Perhaps Yamaha ran out of plugs and installed plug with anode instead !!
Tony Dix
I write this in the hope that it will help others avoid the excessive time and energy trying to solve this problem.
The engine is 7 years old and began to have overheating problems. The symptoms were that all was normal while the engine was working hard. As we approached a dock and began to slow down or after a few secs at tickover the overheat warning alarm would sound.
I was fairly sure that the problem was a bad impellor so I dropped the foot and investigated. The impellor looked perfect but I replaced it anyway. Re-assemble the engine and tried again. No improvement !. I thought it might be a thermostat problem but I removed it checked it in a saucepan of water and it seemed to work well. I tried the engine again with no thermostat installed still no change. I thought it might be the temperature sensor at fault so I removed it tested it in a saucepan with water being heated and it was within specs.
I took of the foot again and attached a garden hose to the bottom of the water tube as it protrudes through the centre mid section of the engine. When water pressure was applied a good stream of water came through the ‘pisser’.
I put the foot in a bath of water and connected an electric drill to the drive shaft and rotated it with the drill and water was being pumped out of the water pump from the hole where the water tube would connect. I was however unsure that the pressure there was good enough since when I blocked the hole with my thumb it was fairly easy to block the stream and when I did this water escaped from the water pump housing from the gap that surrounds the drive shaft. This made me buy a brand new replacement water pump with another impellor and all the other water pump components including the housing.
Installed it ran the engine again no improvement. I begin to doubt my sanity !
There must be some serious internal problems so remove the engine from the boat. Remove the power head, pan, engine sump and inspect. First problem water tube which carries water from the pump up to the power head is badly corroded. Attempted a soldered repair of this copper pipe because a replacement was not easy to obtain or easy to fit. Reassembled the engine and installed on the boat .
No improvement UGH ! What is going on here ? Time to buy a new engine !!
Took the engine off again and another complete strip down of the power head, pan, engine sump and exhaust chamber and inspect again. There are many chambers in the engine sump to power head joint and I was unclear about which chambers carried the water so I use a compressed air gun from the water tube and felt for drafts at the joint this revealed which chamber brought the water to the power head.
A compressed air gun upwards into the power head at this chamber should reveal a draft somewhere eg the pisser tube or the thermostat but I could feel nothing. So there is a blockage in the power head somewhere but where ?
Looking at the port side of the engine you see a long aluminium manifold that runs from top to bottom of the power head its called the outer cover exhaust. At the top of it is the opening for the thermostat. I removed this cover to inspect. Inside I found a pristine looking manifold except for a pile of debris at the bottom of the casting. Poking around with a screwdriver I removed some light crud and then began to see the object was moving when I touched it. A bit more prodding and a pair of needle nose pliers allowed me remove a piece of crud about the size of a cigarette butt. I had no idea what it was but is was clearly blocking an important water passage.
Cleaned the passage reassembled the engine put it back on the boat everything works well. Problem solved !
I took the piece of crud to a local gathering at showed it around. A friend George Hemming recognized it immediately. It was the remains of a pencil anode installed on a brass plug in the engine water system.
The lead anode had corroded near the point where it screws into the brass plug and the remaining piece had fallen into the water chamber eventually completely blocking a hole in the water circulation system.
Many hours of work and a great deal of anxiety caused by this problem. I should have been more careful when I saw a perfect impellor ! I should have given this a great deal more thought.
I hope this tale helps someone. Incidently no mention of this anode in the engine parts book or in the service instructions. Just a brass plug is shown in the parts book. Perhaps Yamaha ran out of plugs and installed plug with anode instead !!
Tony Dix
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