Over heating at idle/low speeds

[Mat1]

I have a 2000 yamaha 70trly. Recently it started having this overheating issue were at idle or slow speeds it overheats. The water pump and thermostat have been replaced with oem parts. I am lost as to why this issue is happening (fresh water motor its whole life). It pees a good stream. when the thermostat was replaced I took off the exhaust cover to see if their was debri in the water jacket and it was clean. My resaerch has pointed me to a popit valve being stuck but this enigine doesnt have one. Any guess to whats wrong? Or recomendations for a water treatment to clean out weeds that could have got sucked in? (I have not hit any sand bars and their isnt much sand in the lakes i go to)

 

[99yam40]

did you ever loose pieces of an impeller in the past

 

[FishMan001]

Not quite the same, but a similar problem on my 70B.
Eventually, I took the head and head cover off, and all the channels were blocked with crud. It also extended into the channels round the bores.
It wasn't a complicated job cleaning them out, but it was quite time consuming.

 

[Mat1]

did you ever loose pieces of an impeller in the past

No, always replaced before it got that bad

 

[Mat1]

Not quite the same, but a similar problem on my 70B.
Eventually, I took the head and head cover off, and all the channels were blocked with crud. It also extended into the channels round the bores.
It wasn't a complicated job cleaning them out, but it was quite time consuming.

Im worried that might be my case too. Just did not feel like taking off the head to check.

 

[JEFF&kelly2]

I have a 2000 yamaha 70trly. Recently it started having this overheating issue were at idle or slow speeds it overheats. The water pump and thermostat have been replaced with oem parts. I am lost as to why this issue is happening (fresh water motor its whole life). It pees a good stream. when the thermostat was replaced I took off the exhaust cover to see if their was debri in the water jacket and it was clean. My resaerch has pointed me to a popit valve being stuck but this enigine doesnt have one. Any guess to whats wrong? Or recomendations for a water treatment to clean out weeds that could have got sucked in? (I have not hit any sand bars and their isnt much sand in the lakes i go to)

 

[JEFF&kelly2]

I have a 2000 Yamaha 80Hp fourstroke that had relatively the same problem. I found that the exhaust is run straight down under the motor and it sucks the water up alongside it, to keep it cooled so it dont over heat. My exhaust and water intake etc. became plugged up with lake water buildup of like calcium type stuff from over the years. Its a process because you have to pull off the power head. But ran like a top after I got it cleaned.

 

[Mat1]

I have a 2000 Yamaha 80Hp fourstroke that had relatively the same problem. I found that the exhaust is run straight down under the motor and it sucks the water up alongside it, to keep it cooled so it dont over heat. My exhaust and water intake etc. became plugged up with lake water buildup of like calcium type stuff from over the years. Its a process because you have to pull off the power head. But ran like a top after I got it cleaned.

So like beneath the motor in the lower casing is where you had build up?