Yamaha 2-stroke 4hp overheat problem

[skarpsynt]

I have a Yamaha 2-stroke 4hp (4AC). At startup there are a nice water flow through tell tale, but after driving a few minutes I noticed the motor was slowing down and steam gets out of tell tale, so I stopped it. I replaced the impeller but it made no difference.

The history of the motor is unknown for me, I got it with a boat, but it should be said that there are cracks in the swivel brackets. They are stabilized with a hose clamp, I don't think it will cause this problem. The motor has probably not been used in salt water.

Any suggestion what to do?

 

[99yam40]

I would check/test the thermostat to make sure it operates in spec

 

[skarpsynt]

You were spot on! the thermostat was clogged. I hope that will solve the problem.

I needed to get the motor running ASAP so I posted the issue at another forum as well. Here comes a link if someone have the same problem and want to read more.

https://www.rib.net/forum/f36/yamaha-2-stroke-4hp-overheat-problem-91328.html

 

[99yam40]

You were spot on! the thermostat was clogged. I hope that will solve the problem.

I needed to get the motor running ASAP so I posted the issue at another forum as well. Here comes a link if someone have the same problem and want to read more.

https://www.rib.net/forum/f36/yamaha-2-stroke-4hp-overheat-problem-91328.html

what was it clogged with?
you may need to clean the whole cooling system if it is real bad

 

[skarpsynt]

I'm not 100% sure, but probably sand and little bit salt that reacted with the copper in thermostat. I will look closer tomorrow, there are still some of this sludge behind the thermostat. The other channels looked pretty good IMO.

I'm not allowed to upload pics here (?!) so please look at the other thread if you want to see. Thanks.

 

[99yam40]

May want to look into a chemical treatment.
Rydlyme marine descaler worked well

 

[skarpsynt]

Thanks for the advice. I suppose a mix of citric acid and water would clean some as well? (I have that at home)

 

[Chris1956]

There was an article on the internet on various chemical flushes for outboards. Some chemicals are pretty hard on the aluminum casting of the engine, and some others didn't work at all. You might check it out before flushing.

 

[crazy charlie]

Thanks for the advice. I suppose a mix of citric acid and water would clean some as well? (I have that at home)

Start with what you may already have on hand like vinegar or CLR. Dont use the dollar store products as they are all watered down with the exception of Simply Awesome cleaner which works great.Charlie