Yamaha 250 SX250 TXRY Overheating

[VANGRADY]

Hi Guys, I am looking for help. My boat has twin '2000 Yami 250 SX's with 180 hours. Last summer my port engine was overheating at various rpm's and after repacing the thermostats, testing the thermosensors and cleaning the PRV, my mechanic narrowed it down to a shreaded impeller. I replaced both waterpumps last fall and shut down for the winter. This weekend on start-up, both engines overheated within about 1 minute of each other at low rpm after warm-up of 10 minutes at (600 - 700 rpm). To summarize, I have replaced T-stats, PRV's and Waterpumps and now both overheat! My mechanic says that he has come across some of the machines that when they are run in the test tank are on the verge of overheat at low idle because the pumps are barely able to pump the water to the top of the head. He has used an infarred heatgun to monitor the temps and some engines are within a few degrees of triggering the temp sensor. This is good information but before all of these problems started, both of my engines could idle for long periods without overheating.
Has anyone else experienced these problems and what would be the next step?
Many thanks.

[robert graham]

sounds like your idles are set a bit low...should be in the 750 to 850RPM range...maybe at increased RPM they pump more water up to engine and cool better...it's worth a try. Good luck!

[Tucker]

If water is coming out of the telltale water must be getting to the heads right?

[VANGRADY]

Before these problems started, both engines ran without overheating for the two years that I have owned them below 800 rpm.
The telltale stream appears to be strong and the same pressure on both machines.
Thank you very much for your comments. I appreciate the time you spend trying to solve the problem.

[jb123]

are you running on the hose or in water....

[VANGRADY]

They run in salt water. I sent Yamaha the same email and they think it is an electrical problem?? This does not make sense to me because I removed both cowls and felt the cylinder heads and thermostat housing and I could only keep my hand on them for about one second. They were equally hot on each bank and on each engine. I also felt the tell tale stream and it was cold. I don't know if the stream should feel cold or warm??

Thanks again.

[jb123]

when you replaced waterpumps did you also replace the housings ?

[VANGRADY]

I was watching my mechanic when he replaced the impellers and he did not replace the ss housing or some of the brass looking washers. I did not say anything as he is a factory trained mechanic who has worked on Yamaha machines for over 25 years and I have almost zero knowledge of outboard engines.

[89 Grady White Project]

I have one of my 2003 250HPDI's overheating and it sounds we've tried the same remedies:
-- Checked for stuck thermostats
-- Good water pump impellers
-- Pressure relief valve (PRV)
I have have the Yamaha computer diagnostic tool with the USB adapter and it works great, but everything is showing up normal except the temperature just slowly climbs until it hits 194 and the computer cuts the ignition back and the alarm goes off. I have noticed the curved housing of the lower unit makes it hard for the typical hose adapter cup to make a good seal, so I've bought the Yamaha brand which helped. I have had the lower unit off and looked at the water flow up to the impeller and its not great, but it does supply enough to fill the engine and produce a stream out of the tell-tale. I noticed the grommet in my PRV was very hard and not pliable, so it may not be making a good enough seal which means not enough water is circulating in the engine. It's a quick check for most of your mechanics, so I would give that a try. Good luck.

[VANGRADY]

Thanks for the information guys. I spoke with my mechanic and he is going to take the pumps apart again on July 10 and see if he missed something. He feels that cause has to be in the waterpump or PRV. He is going to check to see if the grommet on the water supply tube is seating fine and if it is in good shape. He mentioned that when you slide the lower end back on the upper leg, that the grommet can sometimes roll over and obstruct the end of the tube??

I will let you know how I make out.

[Tucker]

I believe if the PRV is stuck open water will come out the bypass ports below the powerhead. Need the pros here to confirm this. Stabing the water discharge pipe in the water pump grommet is a leap of faith if it's like mine. You can't see it when sliding the lower unit on. But, if you have strong tell tail I would doubt that's the problem. My money's on the PRV. Mine was crusted over with salt deposits. It still sealed but I was on borrowed time. July 10! WTF!! You're going to miss July 4th weekend on the boat! What, your guy wants to work more profitable jobs first before he comes back to a problem he can't diagnose??

Help!!

I have a 1988 yamaha 225excel. I am having overheat problems on the right bank of the outboard. I tested the thermo sensors and found it was not the problem. i put new thermostats in both sides and replaced the water pump last year. I have not used the boat since last year and have not had any problems with the motor. I can not keep my hand on the top of the cylinders on either side of motor. the water coming out is cold and not warm. I know its the starboard side of the motor because i have swapped the port sensor with the stapboard and alarm was still coming off the starboard side. What could this be? please help I am writing this for my father and want to have it fixed for 4th of july weekend!!