1994 Yamaha 115HP 2 Stroke Alarm at high rpms

[ezzrider]

My 94 115HP 2 stroke runs fine at low to moderate RPMS or Speed but when I go to higher RPMs the alarm goes off and the motor reduces RPMs, Runs like that for a minute then no alarm and runs fine then alarm again. I do not run it much when this happens. The water pump is not that old and the stream comes out very hard. I do still have the oil injection hooked up though I can run all day a lower RPMs. I use in fresh water. My gauges do not work.

[pstephens46]

Do you have gauges? Are they indicating what the problem may be? Low oil? Overheat? Etc...

missed the last part. No gauges.

[ausnoelm]

Almost certainly partially blocked cooling passages, some will post about using acid/vinegar/ssaltaway and so on, but, in the end, pulling the heads off, and any other access points to dig out the built up crud is your best fix, then take care of possible broken bolts.

[ezzrider]

Do you have gauges? Are they indicating what the problem may be? Low oil? Overheat? Etc...

My gauges do not work unfortunately. Alarm works though! Oil reservoir tank has plenty of oil.

[pstephens46]

Perhaps the thermosensor can be disconnected while alarm is sounding. To confirm it is the issue and not oil. Others will add shortly.....

[pstephens46]

Due to age most likely temp, agreed. Still would be good to confirm 100%. What is the exact model number?

[ezzrider]

Due to age most likely temp, agreed. Still would be good to confirm 100%. What is the exact model number?

115 TLRS is the model number.

[dray0151]

Do you have a service manual for the engine? Not the owners manual.

[ezzrider]

Do you have a service manual for the engine? Not the owners manual.

I have one of those aftermarket manuals but can't lay my hands on it right now dang it. Can't figure out how I can run for hours at low to medium speed no issues until I hit the higher RPMs. Seems like if overheating would happen at the lower RPMs over such a long running time.

[dray0151]

https://www.vansoutboardparts.com/se...a-shop-manuals

Try the link here for your manual. It may be the 115S if it is a 94. It may have better info than one of the aftermarket ones. As stated you might want to start looking at blocked water passages but if this is a freshwater engine they re not as bad as saltwater use. To bad gauges don't work that would help some too. Not a 2 stroke user but just because an oil tank has oil it may not be getting enough through to the engine at rpm's. the manual also has a couple of pages on troubleshooting.

[donsmarine]

1st i'd run it on a portable tank with premix and touch the cyl heads with my finger, careful it might be hot. i think the buzzer turns on around 200 degrees.

[ezzrider]

1st i'd run it on a portable tank with premix and touch the cyl heads with my finger, careful it might be hot. i think the buzzer turns on around 200 degrees.

Thanks. Unfortunately I do not have a portable tank dang it. You think may be the oil not mixing properly from injection system? I am going to pull the boat back out of the water in morning and take a look at the oil lines.

[Jason2tpa]

Use the service manual from link provided above for instructions to test oil alarm sensors and thermosensors. You'll need a multimeter. The easier and less messy of the two alarm systems to test is temp. Pull out the 2 bank sensors to confirm their proper function. If both are good then you've ruled out this being a temp issue, or vice verse.

[panasonic]

I have one of those aftermarket manuals but can't lay my hands on it right now dang it. Can't figure out how I can run for hours at low to medium speed no issues until I hit the higher RPMs. Seems like if overheating would happen at the lower RPMs over such a long running time.

The engine running at low to moderate rpm is making a certain amount of heat that is being removed by the flow of water through the cooling passages. At high RPM the engine is producing much more heat as it is working much harder and the flow of water must increase to remove the heat. So if the cooling system is not working properly and can't keep up, then the engine will overheat.

Sounds like you have partially blocked cooling passages or a bad impeller. It works good enough to keep it from overheating at lower rpm's but not at high RPM. Not unusual.

The manual will tell you how to test the thermoswitch. It may be giving you a false alarm and putting the engine into rpm reduction mode...OR it maybe working the way it is supposed to, sensing the overheat, and putting the engine into rpm reduction like it should.

The oil tank alarm is for low oil level. If the oil tank is low.....that alarm would be sounding at all RPM's. It does not know if the auto lube system is actually working or not.

If the engine is not getting enough oil mixed in with the gas at any RPM there will be no alarm, just a seized engine.

Hope that makes sense.

[zenoahphobic]

The engine running at low to moderate rpm is making a certain amount of heat that is being removed by the flow of water through the cooling passages. At high RPM the engine is producing much more heat as it is working much harder and the flow of water must increase to remove the heat. So if the cooling system is not working properly and can't keep up, then the engine will overheat.

Sounds like you have partially blocked cooling passages or a bad impeller. It works good enough to keep it from overheating at lower rpm's but not at high RPM. Not unusual.

The manual will tell you how to test the thermoswitch. It may be giving you a false alarm and putting the engine into rpm reduction mode...OR it maybe working the way it is supposed to, sensing the overheat, and putting the engine into rpm reduction like it should.

The oil tank alarm is for low oil level. If the oil tank is low.....that alarm would be sounding at all RPM's. It does not know if the auto lube system is actually working or not.

If the engine is not getting enough oil mixed in with the gas at any RPM there will be no alarm, just a seized engine.

Hope that makes sense.

And of course you might be able to check if oil deficiency is the problem by adding 50 to 1 oil to your tank ( mix a small amount if you can empty your tank somewhat), then run to see if alarm doesn't activate.