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Discussion Starter #1
I have a 95’ Yamaha 115 2 stroke on my 1979 Mako 20 CC. At lower RPMs the bot runs perfect and will run all day. My RPM gauge is broke however the speedometer is around 13-14mph where I can cruise and I have no issues. When I run at high RPMs at around 26-30mph the boat will sound the over heat alarm rather quickly and go into limp mode, 5min give or take. I simply put the boat in nuetral rev it up a little to circulate the water, turn boat off and back on sometimes let sit for a minute and alarm is off. I’ve boiled the temp sensors and they’re working, cleaned the pop-it, and had a new impeller put in (pisses like a race horse) and still the problem. The last thing I was told to check is cavitation. My transom bracket can drop down 1 more hole, and the lower unit has a whale tail on it that I just never took off from the guy I bought it from. So I’m thinking I have a cavitation issue and going to drop the motor to the bottom transom hole and possibly take the whale tail offf the lower unit if this could possibly be aerating the water? If anyone has had this problem or has any suggestions please let me know. I’ve also read about some leaky seals possibly and that’s out my mechanical abilities so any guidance for a good shop or mechanic would be great. I love my little boat and just want it running top notch so any help is appreciated. Thanks guys
 

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If its peeing then its taking in enough water. You could have corroded/blocked water passages in and around the heads.

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I have limited mechanical knowledge. Is this something I can check easily by pulling the head covers or should I use a shop? If I need a shop I would really appreciate a recommendation. I’m from LA and moved here in December. I don’t mind paying The right price for the right work.
 

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Discussion Starter #4
If its peeing then its taking in enough water. You could have corroded/blocked water passages in and around the heads.

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i was just reading about some stuff called Nuetra-Salt. Remove the thermostats and pour directly in. Let sit for 1-2 hours and then take water hose and flush straight into the thermostat hole. Then muff the motor and run to flush it out. Have you heard of this and do you think it’s a safe solution without messing up the power head?
 

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Check the intake screens on the lower foot. I removed my lower foot to replaced water pump, then i decided to paint it. I removed the intake screens and when i put them back on the foot, i put them on backwards. The screens will fit either way forward or backward and you can't really tell if they are on wrong. Motor would do exactly what you have described at high RPM. Mechanic took one look at it and immediately knew the screens were on wrong. I put the screens on right right and she purs like a kitten.
 

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Discussion Starter #7
Check the intake screens on the lower foot. I removed my lower foot to replaced water pump, then i decided to paint it. I removed the intake screens and when i put them back on the foot, i put them on backwards. The screens will fit either way forward or backward and you can't really tell if they are on wrong. Motor would do exactly what you have described at high RPM. Mechanic took one look at it and immediately knew the screens were on wrong. I put the screens on right right and she purs like a kitten.
Can you give me a little more description of the intake screens? I pulled the whole lower unit to do the water imepellar. Are you saying just remove the bottom section of the lower unit by the propeller? If the intake screens are backwards would that affect the power of the pee stream? Bc like I said it has a very stron pee stream
 

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There was a well known member on the Hull Truth that made a thread showing him flush his motor in a barrel of vinegar water. The vinegar supposedly would dissolve corrosion in the passages. He used several gallons of vinegar and would run the motor till the barrel got pretty hot. Shut it off and repeat the process for several days. At the end he wound up with some grayish powder residue in the bottom of the barrel that he said was corrosion. I am not saying it is good or bad to do, just passing along the info. The motor he did this on was also a 115 or 130 Yamaha.
 

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THe screens are where you place the ear muffs. They are probably held in place with a single Phillips head screw and captured nut.
 

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I am havìng a problem with my 30hp outboard and ordered StarBrite Engine Flush. Got it today so I will see if it works and report back.
 

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i was just reading about some stuff called Nuetra-Salt. Remove the thermostats and pour directly in. Let sit for 1-2 hours and then take water hose and flush straight into the thermostat hole. Then muff the motor and run to flush it out. Have you heard of this and do you think it’s a safe solution without messing up the power head?

If the motor is not really hot then one or both of the thermostat are bad giving a false reading. You can test by unplugging one at the time. while running. I would run the boat and than when you get the alarm unplug one. We did this on the same motor belonging to a cousin. He had one that was bad. we replaced both. I think they were about 15.00 ea.
 

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Discussion Starter #12
If the motor is not really hot then one or both of the thermostat are bad giving a false reading. You can test by unplugging one at the time. while running. I would run the boat and than when you get the alarm unplug one. We did this on the same motor belonging to a cousin. He had one that was bad. we replaced both. I think they were about 15.00 ea.
I pulled both my thermostats and boiled them in water and they both popped out, I thought this means they are still good?
 

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Discussion Starter #15
Exactly what murfpcola said. Single Phillip's head screw - where you put the earmuffs
AWEOSME!!!...I’m offshore until the end of next week and my fingers are crossed this is the problem. The minute I get in it’ll be the first thing I check and I’ll do a follow up.
 

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I pulled both my thermostats and boiled them in water and they both popped out, I thought this means they are still good?
It just means they opened. But did they open at the right temperature?
Do you know if the sensors are good? Sensors and thermostats are different things.
 

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Discussion Starter #17
There was a well known member on the Hull Truth that made a thread showing him flush his motor in a barrel of vinegar water. The vinegar supposedly would dissolve corrosion in the passages. He used several gallons of vinegar and would run the motor till the barrel got pretty hot. Shut it off and repeat the process for several days. At the end he wound up with some grayish powder residue in the bottom of the barrel that he said was corrosion. I am not saying it is good or bad to do, just passing along the info. The motor he did this on was also a 115 or 130 Yamaha.

Thermostats don’t plug in.

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8611A6D6-2900-4BFF-848D-00D0675857F6.png
It looks like my screens are orientated properly so I guess I may need to do a thorough flush w somevinegar and salt away. I just don’t understand there being blocked passages w the pee stream being so strong.
 

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Discussion Starter #18
It just means they opened. But did they open at the right temperature?
Do you know if the sensors are good? Sensors and thermostats are different things.
Here’s what I boiled and it popped open. I didn’t not check temp. I guess these are the sensors I thought they were the thermostats
1070344
 

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The item in the picture is a thermostat. The thermostat opens at a specific temperature to allow water to circulate.

The temp sensors are an electrical item. They send a signal to a temperature gauge and/or signal the alarm to sound when the sensor determines that there temperature is too high.

The 'pee' tube is in a specific position in the circuit that the cooling water takes through the engine. The pee tube can often show a strong stream while something downstream from the pee tube has an issue. Depending on where the pee tube is in the circuit or path, that something could be a thermostat that is opening properly or completely. There could be some other form of blockage in a cooling passage.

Or, the engine could actually not be overheating - a sensor could be giving a false reading.



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I don’t know the route the water takes but “most” motors pee as soon as you start them up so the stream has no indication of thermostat function. Just $.02
 
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