yamaha overheats

iltfish

Recruit
Joined
Apr 29, 2003
Messages
3
i have a 1999 200hp yamaha saltwater series efi 2 stroke. i just did thermostats and water pump about 2 weeks ago. took boat out for the first time the other day. engine ran great all day, about 45 miles.when i was coming in to my slip at idle, my overheat buzzer went off.i shut down engine immediately and coasted into my dock. pulled engine cover and felt heads.one head was warm while the other head was extremely hot.pulled stats and both are working good.the tell tale has a good stream coming out of it. i pulled the plugs and all were oily so i don't think it is a head gasket. all help would be appreciated
 

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: yamaha overheats

Does the motor have a good pee stream? (Oops sorry you said it does). While you were out did you run aground in any sand or mud? When you replaced the impeller was the old one all in one piece, and did you replace the water pump housing and base plate also? Did you replace both thermostats (you said plural so I am assuming 2) or just check them? You said in your posts that you checked them and they are functioning, how did you determine that? Did you back flush the engine when you had it apart?<br /><br />The fact that one head was hot and the other not suggests a blockage in the cooling system. Number 1 on the list would be 1 thermostat in a multi-thermostat system. Which cylinder was hot, top, bottom, left, or right?
 

iltfish

Recruit
Joined
Apr 29, 2003
Messages
3
Re: yamaha overheats

it is a v6 and i checked the stats in a pot of water with a digital thermometer while i heated the water. i did replace the entire pump housing, base plate, orings, and woodruff key.
 

iltfish

Recruit
Joined
Apr 29, 2003
Messages
3
Re: yamaha overheats

it is a v6 and i checked the stats in a pot of water with a digital thermometer while i heated the water. i did replace the entire pump housing, base plate, orings, and woodruff key.<br />someone suggested to me that it could be a pressure relief valve stuck open. what do u think?
 

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: yamaha overheats

Someone else with more knowledge of your engine should know, I don't know the plumbing but I would say its possible. Are the pressure relief valves accessible without going into the engine? Do you have a manual, if not now is the time to get one, it is these engine specific questions that manuals can answer. Since only one bank is hot it would seen that adequate water is getting to the powerhead (not the impeller or tubing gromets) but its getting blocked on one bank. You've apparently ruled out thermostats so its either a blockage in the head or something like the pressure relief valve.<br /><br />You never did say anything about the quality of your engines pee stream.
 
Top