Yamaha Overheating???

[Combee]

I was wondering if someone could help me with a little advise? My engine has been overheating at lower RPM’s. If I run at over 4000 RPM’s the motor runs great and doesn’t overheat, but anything below 4000 the motor will overheat. I have replaced the water pump and the thermostats and it is still overheating. The motor is a 1993 Yamaha Pro V 200. <br /><br />Any suggestions on what could be causing this? Thanks for the help. <br /><br />Dan

 

[rbu]

Re: Yamaha Overheating???

I have been going through some overheat problems lately myself. I haven't quite figured mine out yet, but it seems that I have a sensor giving erroneous readings.<br /><br />Anyway, I've found that a lot of overheat problems center around the bypass valve,(poppet valve). If you haven't opened it up and cleaned it out, I would start there. I have also heard that if the spring is old, you might want to replace that as well.

 

[rickdb1boat]

Re: Yamaha Overheating???

If you don't mind me asking, how do you know it's overheating under 4000 RPM'S? Is the horn going off or does something else happen that leads you to that conclusion?

 

[Combee]

Re: Yamaha Overheating???

Rbu<br /><br />Someone else I talked with suggested the bypass value. The problem I’m having is I’m not quite sure where this poppet value is located. Can you give me an idea what and where to look for it at?? Thanks!<br /><br />Rickdb1boat,<br /><br />Yes the buzzer is going off after I run the boat for awhile under 4000 RPM’s. I was recently in the Keys and was running in a little chop so I was keeping the boat under 3800 RPM’s. After running for about 5 miles the buzzer went off. Shut down waited a half hour ran another 4 to 5 miles and the same thing happened. By this time I was very close to the channel that took us back to our room. We shut down again and waited twenty minutes and took off. I ran at 4800 RPM’s for almost ten miles in this protected channel and the boat ran great! The whole way home I was running close to 18 psi on my water pressure gauge. When I run under 4000 RPM’s I lose water pressure for some reason????<br /><br />Thanks for the help!!<br /><br />Dan

 

[Combee]

Re: Yamaha Overheating???

^

 

[mabbott]

Re: Yamaha Overheating???

When was the last time you replaced the water pump impeller? If it is worn you may not be getting enough volume at lower rpms.

 

[Combee]

Re: Yamaha Overheating???

mabbott,<br /><br />The impeller is brand new. Both the impeller and thremostats were changed the first time the motor overheated. I think it might be that poppet value like a couple of people said. Now if I could just find it. Does anyone have an idea where to look or what to look for??? <br /><br />Thanks again<br /><br />Dan

 

[rbu]

Re: Yamaha Overheating???

The poppet valve is located just below the micro computer. There is a hose running to it. The cover looks similar to a T-stat housing on a car engine. There should be 2 bolts that hold it in.

 

[Combee]

Re: Yamaha Overheating???

rbu,<br /><br />I located it this weekend and took it apart. I’m a little worried because it didn’t look that bad. I clean what needed to be cleaned and I’m going to run the boat and see what happens. Hopefully that’s it!!<br /><br />Thanks again.<br /><br />Dan

 

[ob]

Re: Yamaha Overheating???

Combee, does fly wheel or block seem hot on engine when getting alarm.I would also consider ,after feel check on engine,changing thermo sensor if poppet valve is not problem.

 

[rbu]

Re: Yamaha Overheating???

From my experiences, they don't really go bad, they are just a plastic plug. What happens is that they stick in their seat or there is not enough water pressure to force it open all of the way or they get clogged up. I read on another forum a guy with a similar problem. He pulled the poppet valve out and ran the motor. He could not duplicate the overheat. He was told that over time, the spring can get harder to push together. Just get a new spring.<br /><br />If the poppet doesn't solve your problem, then I would suggest verifying 100% that you are overheating. My engine has been "overheating" however, when I pulled the cover and felt the cylinder heads, they were cool enough for me to hold my hands on for a few seconds. So then I pulled the leads to both thermo-switches and ran her. The rev-limiter kicked in again. So I unplugged the thermo-sensor, ran her and as expected, no rev-limiter since all heat sensors/switches were disconnected. Plugged the thermo-sensor back in and I could not duplicate the problem. Plugged the switches back in and still no overheat alarm. Who knows? Weather and a wedding kept me in this weekend.<br /><br />One last thought, just be sure your rev-limiter is not kicking in due to low oil. You don't want to be chasing the wrong problem.<br /><br />Good luck.

 

[Combee]

Re: Yamaha Overheating???

Thanks everyone! I let ya'll know how it turns out!<br /><br />Thanks again,<br /><br />Dan