1962 Scott 43 hp Cooling Problem

[grassgd]

Cannot get water pump to cool at idle or fast idle. Getting some water streaming from water pump tell tale hole but not enough to get water to cool motor - gets hot and not water coming out with the exhaust. New impeller, and pump housing is good shape. Seems to have excessive bypass of the impeller---can blow air backwards through pump --- I put large rubber washer between stainless steel water pump plates to force water pump plate to impeller clearance to be reduced which helped but not enough. If I put larger rubber washer in, it almost stops ability to blow air backwards but cannot turn propeller shaft/water pump due to binding of water pump impeller.......Don't know what else to try. Anyone have any suggestions?

 

[F_R]

You need to revisit that water pump and figure out which part is not to spec. You should not be needing to shim stuff. Where did you get the new impeller?

 

[flyingscott]

Did you put the waterpump in right it only goes one way? there is only an o-ring in there between the 2 stainless plates. Is the compression fitting on the water tube itself? Those use compression fittings to seal the water tube if it is split the water shoots out the seam. Does that motor have a thermostat on it? Did the old impeller come out in one piece?

 

[grassgd]

You need to revisit that water pump and figure out which part is not to spec. You should not be needing to shim stuff. Where did you get the new impeller?

I know you should not have to shim the water pump, but with the water pump installed in the lower unit and submerged in a tub of water, I could easily blow air from the pump discharge out the intake in the lower unit. Turning the shaft by hand, the pump would hardly move water out the pump discharge. I examined the SS plate that goes on top of the pump with a straight edge and noticed a slight curvature which would provide clearance around the central part of the impeller (near the shaft). I checked another water pump plate from my spare parts engine and it showed the same. I straightened out one of the plates and tried the air test and hand pump test again with a slight improvement. When I put the rubber washer between the pump SS plates which actually reduced the clearance between the water pump impeller to the plate, I saw a pretty good improvement in the air test and hand pump test. Placing a tube on the pump outlet and turning the pump as fast as I could by hand, I could only get the pump to lift the water about 30 inches which is about as high as required to reach the engine. Placing a slightly thicker (about .030 thicker) rubber washer in, the air by past test improved a lot but I could not turn the shaft anymore... I thought the impeller should perform as a positive displacement pump and not experience the by pass I am seeing. I actually have two new impellers I purchased from Langs some time back and am using one of them.

 

[grassgd]

Did you put the waterpump in right it only goes one way? there is only an o-ring in there between the 2 stainless plates. Is the compression fitting on the water tube itself? Those use compression fittings to seal the water tube if it is split the water shoots out the seam. Does that motor have a thermostat on it? Did the old impeller come out in one piece?

Yes the impeller is installed correctly. One of the run test I did at high rpm's it was pumping very good but at idle and fast idle (with the stop working to prevent high rpm in neutral) weak flow from the pee hole and none coming out with the exhaust......and that was with only the o-ring installed between the 2 ss plates. The water pump seals are in good working shape - actually made new ones from various stock rubber hoses therefor not split or leaking.. When I place a hose on the intake of the lower unit (tube inserted up the copper intake tube to the water pump connected to a garden hose, all is well, engine runs cool at idle with good water out the pee hole and the exhaust. Without the garden hose - force feeding the pump, I do get a stream out the pee hole (not nearly as strong as with the garden hose) but at idle or fast idle no water coming out with the exhaust and engine begins to run very now fast. The pee hole stream improved a lot with the rubber shim washer installed between the 2 SS plates but apparently not good enough to make it through the engine and out with the exhaust.

The old impeller was in good shape with some ware on the impeller tips but not cracked or broken.

It's a shame because the engine is in excellent shape (no corrosion) and starts with just a bump of the starter and idles/runs like a new engine.

 

[flyingscott]

How was it pumping before you replaced the impeller? Did you check the water intake? Did you put it in a barrel with the water level above the waterpump? Does the motor have a thermostat? Is the stainless plate showing a lot of wear? It sounds like you might have a blockage somewhere. There is another rubber fitting under the waterpump housing on the intake tube did you check that one?

 

[grassgd]

How was it pumping before you replaced the impeller? Did you check the water intake? Did you put it in a barrel with the water level above the waterpump? Does the motor have a thermostat? Is the stainless plate showing a lot of wear? It sounds like you might have a blockage somewhere. There is another rubber fitting under the waterpump housing on the intake tube did you check that one?

The engine has been sitting in my garage for the last 15 years or so. Ran fine back then with no cooling problems with a new impeller I installed back then. Decided to pull it out and felt a new impeller should be installed due to age and setting.The water intake is all clear - I pulled the intake tube out and re-installed - no blockage there. All the run test, air test and hand pump test i did were with a tub of water up to the top of the water pump. The SS pump liner and SS cover plate are not worn and look good other than the slight concave condition I described and tried to correct on the plate that is currently installed. I do not think there is a blockage on the system above the water pump because with the garden hose force feeding the pump while in the tub of water or without the tub (like a modern fresh water flush adapter) there is plenty of water flow through the engine and it runs cool at any condition.

I don't know if the engine has a thermostat or not- the service manual does not show where it would be located and it it is on the bottom of the power head/engine block, it's been 15 years or so since I had it apart.

 

[flyingscott]

You may have got a bad impeller and putting the rubber shim in could have made it worse, the hub could be spinning. Try the old impeller and see what happens.

 

[grassgd]

You may have got a bad impeller and putting the rubber shim in could have made it worse, the hub could be spinning. Try the old impeller and see what happens.

Pulled the Scott off the boat to install a modern outboard motor to use it now. I will pull the impeller out and verify if it may be spinning on the hub but I don't think so since when I installed the thicker rubber washer to flex the stainless steel cover plate to reduce the clearance between the plate and the impelled, I could not turn the lower unit shaft driving the pump impeller. When I pull the impelled out, I will verify if the impeller thickness is different (less) than the one I pulled out and the other new impellers I have. These impellers are smooth on the top and bottom surfaces (not the end of the blades) as compared to some modern impellers that have a narrow ridge to form a seal between the top and bottom of the impeller to the housing. I my case it appears there is too much clearance allowing water to simply by pass the impeller vanes at slow speeds. ..... It may be a while before I get to work on it again though.