Tohatsu water telltale pressure

[mattsaks]

On my 90hp, when it runs higher rpms it loses pressure out of the water telltale. Is this normal? It still flows but not as strong as at idle.It has a new water pump. Thanks

 

[Navigator]

Re: Tohatsu water telltale pressure

Mattsaks,<br /><br />Lower water pressure at higher RPM's are usually a sign that the water pump impeller blades are bent in the wrong direction. (water pump impeller installed incorrectly) When this happens, the pump pumps strong at idle, when it is acting in the compression pump mode, but when RPM increase and the pump turns into a centrifugal pump, the pressure drops considerably. As you lower the RPM, and the pump switches back to the compression mode, the pressure will return to a strong stream.<br /><br />Pull the lower unit and check the direction of the impeller blades. The blades should be bent forwards (towards the direction of rotation) when the engine is running. <br /><br />If they are facing backwards, simply reinstall the impeller and all should be great.<br /><br />Nav

 

[mattsaks]

Re: Tohatsu water telltale pressure

ok, i have it apart. the impeller blades were ponting in the same direction as the driveshaft rotates. now when i put it back together and turn the driveshaft by hand (with the hose on it!) the blades flip over and end up facing the other way. this way looks right to me. is this how they should be? does this mean that it was installed wrong to start with and somehow didnt sort itself out? or is it the wrong way now?

 

[Navigator]

Re: Tohatsu water telltale pressure

The blades should always be pointing towards the direction of rotation. The impeller should also be a real snug fit. <br /><br />Typically, there is not enough room for the blades to "reverse directions". If yours reverses when you turn it by hand you may want to check the following:<br />1.Is the impeller the correct one for that engine?<br />2.Is the impeller housing corroded or is it smooth inside?<br /><br />Turning the shaft while dry could cause the blades to reverse, but you said you had the hose on it. If there is any corrosion on the inside of the pump housing, it could catch the blades and cause them to reverse.<br /><br />It sounded like they were facing the correct way when you started. I check everything once again and reassemble, making sure of the blade direction.<br />Test run it again and see if you're still having the pressure loss now that you know everything is installed correctly.<br /><br />One more thing, you said it was a new water pump impeller. What happened to the old one. Was it damaged or simply worn out? If you still have it around and it was just worn, compare the two impellers to make sure they are identical. you could even put the old one back in and see if you get the same drop with it.<br /><br />Let us know what you find out. If all is good we can look at what else might be the problem. either way, we can rule out the impeller as the culprit.<br /><br />Nav

 

[TOHATSU GURU]

Re: Tohatsu water telltale pressure

The blades should be pointed away from the direction of the driveshaft rotation.