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Poor Cooling year 2000 40 HP 2 stroke

S

swamphox

New member
I have owned this motor for several years and it seems to have always had a cooling problem. And the cooling problem seems to stem from poor water flow caused by low water pump head pressure (if that is an apt term in this space). I have a couple questions about the whole water pump/cooling system.

I have a new water pump installed with new housing and everything associated with the water pump parts...just have to saythat because everyone is going to tell me to change the impeller. Its new.

I have just run 4 hours of descaling and I don't even know if it needed it. Even with No thermostat in the housing it always has very weak pressure from the tell-tale unless the RPM are relatively high. The motor will overheat (alarm) if sitting idle in the water (not on a hose) for 5 minutes.

I have no clogs, I have a run the motor with a hose attached to the pipe that comes from the water pump with the lower unit removed and the motor just runs great this way. Of course there is none of the load from the shaft or the impeller and that help a little I am sure. I put the lower unit on and after just a few minutes, the water starts to steam on a hot day in July. Not Good.

Are there high performance or high(er) flow water pumps made for these motors? I know I have a cheap chineseum water pump kit in there now. Could an Yamaha OEM water pump provide that much more flow than a cheap knock off can? I need to fix this problem.video without lower unit running
Lower unit with drill powered pump
Without know what speed at which the shaft is spinning in the drill compared to idle rpm, I think the water volume and pressure is rather weak.

Any help is appreciated.
 
Buy an EOM Yamaha kit. You wasted countless time to save a few bucks.

And when installing the pump cover twist the driveshaft clockwise looking down while pushing the pump cover down. This wil fold the vanes the correct direction.
 
I am looking for better performance not seeking the basic installation and I am well aware of the rotation direction of the water pump impeller. The only part that has been changed out on the water pump is the impeller. You are telling me that the yamaha impeller is of superior quality and tolerance that this will increase performance boost pump pressure to a level not seen in this motor, ever. I have much doubt.
 
You can believe what you want.....
I have seen many people push the vanes over & squash the cover down. Vanes end up going both ways & don't flip over in use. The best way is a film of oil or grease in the pump cup, then rotate the shaft CW as you push it down..... just saying.
Amazon Chineesium junk is junk.
Yamaha did build & still builds a quality motor. Their OEM parts work.
 
Your 1st post in paragraph 2 states:
I have a new water pump installed with new housing and everything associated with the water pump parts...

Your 2nd post states:
The only part that has been changed out on the water pump is the impeller.

You can't have both.
 
I agree. However, these pumps seems to be way under performing. The pressure coming from the lower unit seems insufficient by a large amount.
 
The reason I am hesitant to pull off head cover and water jacket cover is that fear of snapping a bolt. I know the torque is pretty low on these head cover bolts but....
 
swamphox said:
The reason I am hesitant to pull off head cover and water jacket cover is that fear of snapping a bolt. I know the torque is pretty low on these head cover bolts but....
Click to expand...
Start with the cylinder head first, it will tell the story, if its clean then you can dig deeper.
 
Its under performing because it does not move enough water to cool the motor unless the motor is operating at a high RPM. The flow of water seems very good when I have a hose attached to the pipe that goes to the powerhead. I connected a drill to the drive shaft and spun the pump and what appeared was very weak pressure and volume out of the water pump. Very unscientific I would expect a higher amount of water.

The original question was about getting a higher performance or higher pressure/volume water pump for this motor. AND, is the OEM that much better than a cheap copy. I have the original housing and plate, everything else is new. I change the impeller every year and really only run the boat for one week a year. It always overheats if at idle for several minutes and the tell tale is really weak at low RPM, give it a little throttle and the tell tale pressures right up.
 
Well, maybe that when you ran the engine with the lower unit removed and had a water hose coupled to the water tube, you were exceeding normal water pump pressure and the engine ran cool. I'm in the camp that you have deposits up stairs that has nothing to do with the impeller. It would explain a overheating condition at idle and adequate cooling at higher speeds since water pressure increases with RPM's.
 
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