SX225 OX66 Overheating at Cruise

[stf26]

I have twin 225 OX66s on my boat and have had some issues with overheating recently. I was hoping to get some advice from someone on the site. The engines are model year 2000 and have been maintained very well including a flush after every run. I have changed the water pumps every 3 years. I just changed the water pumps before last season and had zero issues with overheating at cruise during the entire season. This season is a different story. If you run the boat for about 5-10 minutes at 4000 rpms the overheat alarm will go off. There is a good steady stream of water coming from the tell tale. If you put the engine in fast idle it stops the alarm in about 30 seconds. I have used an infrared temp gun to measure both engines to try to understand what is going on. The engine that has the overheat issue measures at 175-185 during the alarm which is definelty a problem. The other engine meausures 120-130 which seems about right. This rules out an issue with a sensor. For good measure I have replaced all of the thermostats and related gaskets. I have also checked the pressure release valve located on the water jacket and it is free and clear of any debris. After all of that it still overheats.

All of this being said my next step is to haul the boat tomorrow and check the water pump housing and impeller. I am hoping that I might have a crack in the housing or something wrong with the impeller. Hopefully it is the housing not the impeller because I will have to go searching for the impeller debris if it is really torn up.

If the impeller and housing checks out what would be the next step? Any ideas would be much appreciated.

[jb123]

you should change the pump kits every year, I also do the stats and prv's also at the same time.
if you think you have thermosensor issues, swap with the good motor and see if the issue follows the sensor.
did you recently add anything to your transom, causing any light cavitation to intake ?
lastly you could pull the water jackets, clean and reprime them.

[stf26]

Nothing new on the transom. Definetly does not seem to be a thermosensor issue because I confirmed the overheat with a infrared gun. It is definetly over 180 when the buzzer goes off. The other motor is at 130-135 when the alarm goes off.

I am going to inspect the water pump closely tomorrow to see if something is wrong with it. I might be able to get a pressure guage from my yamaha dealer that would help to make sure that I am getting the proper psi at cruise speed.

I am really hoping that I do not have any corosion in my water jackets. It really would not make much sense because I was so careful to flush it after every use.

[jb123]

what i do know is that yamahas are very finicky when it comes to cooling/water flow....they need the max., and dont like any interruption/restriction.
I had a simlar issue this weeekend....afer short wake zone, port goes off...and wont go back off...for eight miles...had to run on on starboard...tried it again and it cooled down a bit, fine for the rest of the day.
Again, i suggest replacing rather that checking.

[stf26]

I am on my way now to our Yamaha dealer to get some parts. I am definetly going to get new waterpump kits for both engines and the new and improved PRVs. I am also going to try to get a water pressure guage from them so I can test them this morning before I haul the boat. This way I will have a baseline for before and after the pump change. I am definelty crossing my fingers that the pump has something wrong with it. I am going to post the outcome of all of this once I figure it out. I hope that it will be helpful for someone else who is having the problem.

[stf26]

Well good news! I replaced the PRV with a new and improved mushroom style part. We then hauled the boat and dropped the lower units. The only visual issue that I could see with the water pump on the engine with the overheating problem was that the o-ring on the outer pump housing might not have been seated properly. No burnt outer plastic housing. Impeller was in very good condition. For good measure I replaced the plastic impeller outer housing and the gromet in the water exit tube. FYI These parts are not part of the water pump repair kit.

After dropping the boat back in the water we started the engines and I could immediately see a difference in the volume of the water coming out of the tell tale. After running the boat for 10-15 minutes at 4000 rpms I stopped and used the infrared thermometer on the motor that had the overheat issue. The temperature on the termostat housing was about 125-130 deg (f) which is well within spec.

Also, I learned a cool trick from someone at the marina on how to remove the key on the shaft. I used to use a chissel to hammer it out. A pair of wire cutters is a much better route. You can use them to pry the key out without any hammering. You can put something on the shaft if you are nervous about banging it up while prying.

I hope that this post will help someone else in the future.