2002 70BETO Overheating Alarm at idle

[JPJ]

Stuy,

Which parts(seals) did you get again? Much appreciated!


JPJ

[Stuy1980]

Ok.
So finally got the boat out on the water today. Run it for about 30min at half speed. Then sat at idle for about 5-10 min and thought everything was fine then the bloody alarm went off again. Turned motor off and drifted for about 10min until i had to start the motor to avoid moored boats. Alarm came back on. But only lasted about 2 min then went off... Im pretty much out of options now. Can only put it down to a electrical issue or bad sensor. Does anyone know where the temp sensor is located and how easy is it to change?
Cheers

[Stuy1980]

Found the thermo switch. Pulled it out and put it in a pot of water and heated it up with a thermometer and multimeter to see if it was faulty. But it closed at about 90c so im assuming this is working. Need more ideas.
What else can i check?

[McYamaha]

Saw this post from a few years ago . I am having the same issue with a 2000 70 hp Yammi 2 stroke with 100 hrs. The motor runs fine but temperature alarm goes off when idling on the muffs and in the water after about 5 minutes. If I run the motor at 1500 rpm it goes off. I have changed the water pump impeller, top housing, stainless cup and base plate. There is a black rubber piece that sits under the top housing in the hole for the water tube to the engine. There are no seals around the drive shaft and stainless cup and impeller. Not sure if this is correct but that is how I found it. Also changed thermostat.
The problem was still evident after replacing the water pump parts ( not oem ..not sure if this is the problem). I then removed the head and exhaust cover and checked water passages and cleaned what little scale was there. I then pushed some wire down the water tube and was all clear. I also check the thermo switch operation in hot water and seemed to operate around 85 to 90 deg.
After all this the alarm still went off when idling when I took it out the other day so I’m at a lost as to what to try next other than visit a Yamaha service centre.

[SkeeterJohn]

Saw this post from a few years ago . I am having the same issue with a 2000 70 hp Yammi 2 stroke with 100 hrs. The motor runs fine but temperature alarm goes off when idling on the muffs and in the water after about 5 minutes. If I run the motor at 1500 rpm it goes off. I have changed the water pump impeller, top housing, stainless cup and base plate. There is a black rubber piece that sits under the top housing in the hole for the water tube to the engine. There are no seals around the drive shaft and stainless cup and impeller. Not sure if this is correct but that is how I found it. Also changed thermostat.
The problem was still evident after replacing the water pump parts ( not oem ..not sure if this is the problem). I then removed the head and exhaust cover and checked water passages and cleaned what little scale was there. I then pushed some wire down the water tube and was all clear. I also check the thermo switch operation in hot water and seemed to operate around 85 to 90 deg.
After all this the alarm still went off when idling when I took it out the other day so I’m at a lost as to what to try next other than visit a Yamaha service centre.

I'm having the exact same problem with my 1998 OX66 200hp. I've replaced everything water pump related. I can run it at any speed except idle just fine. I can run wide open all over the lake and it's fine. I can heavy idle, where I'm creating a little bit of wake and I'm just fine. But if I just putt around slowly running my graphs for a couple minutes the alarm goes off every time. I kill the motor and sit for five minutes then crank it and run it around and it's fine. As long as I don't idle slowly I"m good.

I'm wondering if it's an exhaust issue? Where exhaust pressure if building up at the slow idle.

[panasonic]

Hello McYamaha
Could you start a new thread with the description of the problem in the title. And include your exact model # and serial number in your first post.

Thanks

[99yam40]

to start a new thread, click this link and then the new topic button at upper left of screen
https://www.yamahaoutboardparts.com/...outboard-forum