I had my mechanic come down and do a dockside test with with his Thermometer to check out my low idle overheat issue on both engines. Of couse when he was ther it did not happen. His theory is that since we had a very cold winter, the wax in the T Stats might have hardened and it might have taken one or two times of starting and running the engines to loosen up the T Stats. Does this make sense to owners who keep their boats in cold climates? We started up the engines and after about 8 minutes, the top cylinders reached 150 deg and then quickly dropped down to 106 deg after the T Stat opened. Both engines ran at this temperature for about 40 minutes without an issue. The mechanic also took apart the PRV's and they were both clean. I still do not know if I have a problem that is intermittant or if it is solved??
Yamaha 250 SX TXRY Overheating
- Thread starter vangrady
- Start date
My boats have seen extended periods below freezing and never this issue. I would doubt his statement. When was the last time you replaced the T-stats? They should be changes every two years. When was the last time you replaced your water pump impeller? Do you fresh water flush after every use assuming that you are in salt water?
I would start with replacing the t-stats and gaskets, while you are at it take a good look at the cooling passages if there are any salt deposits you have your first clue as to what is wrong. I would bet that you have a t-stat that is fouled with salt deposits. I would also check the water pump impellers if you have not replaced them in the last 300 hours or if you run in an area with a lot of sand or mud.
I would start with replacing the t-stats and gaskets, while you are at it take a good look at the cooling passages if there are any salt deposits you have your first clue as to what is wrong. I would bet that you have a t-stat that is fouled with salt deposits. I would also check the water pump impellers if you have not replaced them in the last 300 hours or if you run in an area with a lot of sand or mud.
Hi Tashmoo;
My mechanic replaced the T-Stats, Water Pump Impeller, cleaned the PRV valve and tested the thermosensors. My boat runs in saltwater. I ran the boat this last weekend and everything ran fine so I don't know if the problem has gone away or it is intermittant.??
My mechanic replaced the T-Stats, Water Pump Impeller, cleaned the PRV valve and tested the thermosensors. My boat runs in saltwater. I ran the boat this last weekend and everything ran fine so I don't know if the problem has gone away or it is intermittant.??
I am thinking the same thing. At this point, I will change the T Stats in both engines and run the boat as much as possible to see if it overheats again.
The engine head temperature reached 150 deg and then dropped down to 106 deg when the T Stats opened. The T Stat housing temperature was 138 deg. Is it normal to have the T Stat housing temp higher than the engine head??
Thanks again guys.
The engine head temperature reached 150 deg and then dropped down to 106 deg when the T Stats opened. The T Stat housing temperature was 138 deg. Is it normal to have the T Stat housing temp higher than the engine head??
Thanks again guys.
You didn't say if the telltails were strong at idle when the problem occured.
I don't buy the cold wax idea one bit. I don't know what previous maintenance was done on the motors but the fact that both engines exhibited the problem at the same time is strange. I am leaning towards worn impellers. Were the motors in the water when the issue occured or were thay on muffs?
In any event, the fact that they ran good on your last trip is encouraging.
I don't buy the cold wax idea one bit. I don't know what previous maintenance was done on the motors but the fact that both engines exhibited the problem at the same time is strange. I am leaning towards worn impellers. Were the motors in the water when the issue occured or were thay on muffs?
In any event, the fact that they ran good on your last trip is encouraging.
Hi Seasick;
The engines have 185 hours on them and the impellers and T Stats were changed last September and the PRV was also cleaned out at that time. The engines were running in the chuck and not on muffs when they were alarming. Last year, my port engine was overheating at various rpms intermittantly and my mechanic discovered that the impeller had come apart from the plastic hub and shredded. This seemed to explain my problem at the time. On my first two start ups of this season, both engines alarmed within about 1 minute of each other at dockside idle. When I increased the rpm to 1200, the alarms stopped after about 30 seconds. I think this is why the mechanic is assuming that the T Stats wre sticking shut.
The engines have 185 hours on them and the impellers and T Stats were changed last September and the PRV was also cleaned out at that time. The engines were running in the chuck and not on muffs when they were alarming. Last year, my port engine was overheating at various rpms intermittantly and my mechanic discovered that the impeller had come apart from the plastic hub and shredded. This seemed to explain my problem at the time. On my first two start ups of this season, both engines alarmed within about 1 minute of each other at dockside idle. When I increased the rpm to 1200, the alarms stopped after about 30 seconds. I think this is why the mechanic is assuming that the T Stats wre sticking shut.
I'd check the poppet valve to make sure they're clean. I had similar issue a few years ago where the alarm would sound at idle but quit once the RPM were increased.
The waxing your mechanic talked about, I have seen that with mine. 2 years ago my port side engine lost its tail tell. and overheated at the dock. I shut it down let it set and started it up and it worked ok. I left the dock and got 5 or 6 miles off shore and it overheated. Limped in on one engine. removed the t/stats and found the wax under the stats about 1/2 inch thick. Flushed the ports out with water hose pressure, cleaned the stats worked all year ok.
Thermostats
Bottom line - t-stats are cheap in comparison to shop labor to diagnose the problem. You can do them yourself in an hour at the most. What the hell, why not?? I'd call Andy at SIM and get them winging their way to you.
Bottom line - t-stats are cheap in comparison to shop labor to diagnose the problem. You can do them yourself in an hour at the most. What the hell, why not?? I'd call Andy at SIM and get them winging their way to you.
Boats Rock said:
I believe that the mechanic was referring to the wax that is inside the thermo's expansion chamber. If you had 1/2 inch of wax in the thermo's housing, it was from something else.
Note that if the pump is working, the telltale will work regardless of whether the tstats are open or closed. In other words, they won't tell if a tstat is bad.
The engines would not reach alarm temp in a minute if the tstat didn't open. That wasn't it. Loss of water flow could result in a quick alarm. You don't have a tstat problem. Again, was there solid telltale when this happened?vangrady said:
If you had an impeller shread, the shreadded stuff can get pumped into the motor. It can plug water chambers, and foul poppet valves. I am leaning to a bad poppet valve. I don't see how both impellers could fail d at the same time, unless there were the wrong model or installed incorrectly ( a good poosibility if that was the same mechanic who told you the wax was cold
Just a wild guess but if the mechanic put the impellers in the cups with the wrong rotation that might just cause your problem, low flow at low RPM. Does anyone know if the impeller is twisted into the impeller cup with the wrong rotation if it will reset to the correct position? Or will it always bend in the wrong direction? My guess is that it will stay in the direction that it was installed. If so it would explain why both engines are having the same problem.
For both T-stats in both engines to be bad is a long shot, possible but a long shot. I would look at the mechanics work it is way too coincidental in my experience that both engines are acting up.
For both T-stats in both engines to be bad is a long shot, possible but a long shot. I would look at the mechanics work it is way too coincidental in my experience that both engines are acting up.
Tashmoo said:
Some folks say that the vanes will reset if the impeller is installed backwards. I, on the other hand, believe that not only will they not reset, but that the could be destroyed. I think the actual truth depends on the specific impeller and motor. For my Yami, I don't see how the impeller vanes could flip over without a tremendous amount of force and most likely damage to the vanes.
The ket piece od evidence in the original post is that both engines had the temp alarm at the same time. That is too much of a coincidence for me. It has to be something that was done to both engines.
Perhaps the impellers are the wrong model.
I had another thought. If the impellers were changed at the same time or even if they were changed at different times AND the wrong impellers were installed, that could explain the issues. Let's say that the impellers are smaller than required. They would not be as tight a fit as the correct ones. During layover the vanes take a set. On start up, the vanes are not making good contact with the pump housing so water flow is reduced. As the water warms up from the motor running, the vanes soften up a bit and the centrifugal force makes better contact with the housing. These impellers should be a really tight fit in the housing.
If the mechanic used the wrong impeller on one motor, there is a good chance he used the wrong one on the second motor also.
I have seen overheating issue where an impeller that was a bit less thick than the oem was used and that also resulted in overheating.
I know I have asked this several times but were the telltales weak when the engine was first started? If the impellers are incorrect, I would expect weak telltales that improved as the motor warmed up.
If the mechanic used the wrong impeller on one motor, there is a good chance he used the wrong one on the second motor also.
I have seen overheating issue where an impeller that was a bit less thick than the oem was used and that also resulted in overheating.
I know I have asked this several times but were the telltales weak when the engine was first started? If the impellers are incorrect, I would expect weak telltales that improved as the motor warmed up.
Hi Guys;
Thank you for your input into my problems. The tell tales have a strong equal flow. I have spoken to a couple of very experienced mechanics (30 yrs +) and they both say that if the impellers were installed in reverse, that they would re-orientate themselves when the engines were started. They were both replaced last September and I ran the boat twice in the fall without overheating. It only happened after the winter layup.
Thank you for your input into my problems. The tell tales have a strong equal flow. I have spoken to a couple of very experienced mechanics (30 yrs +) and they both say that if the impellers were installed in reverse, that they would re-orientate themselves when the engines were started. They were both replaced last September and I ran the boat twice in the fall without overheating. It only happened after the winter layup.