94 force 120 water pump problem

[shovelheadnc66]

Hey guys first post maybe y'all could help me. 94 force 120 blew head gasket from overheating replaced head gasket pump impeller and thermostat. My new impeller had the wrong inside diameter, too small so I turned the id down to the same size as my original one. Everything else was exactly the same. Put it together made sure keyway made contact started it up no water. No water with thermostat out either. Took foot off again put water hose on pickup tube water flows freely through motor. Assuming no blockage. When I take the foot off water does come back down the pickup tube. So my hypothesis is that the new aftermarket impeller is not strong enough to push the water all the way up the tube to the motor for some reason. I tried using the ear muffs and a 30 gallon or so tub still no water just steam in the thermostat housing. Does the motor itself supply enough vaccum to help the water pump pull water into the block? I don't know just shooting in the dark at this point. Thanks.

 

[MickLovin]

I have heard of the side exhaust gasket causing this problem, but others here may have other causes.

 

[Frank Acampora]

There were several different water pumps and impellers used from year to year. If the ID for the impeller you bought was too small then undoubtedly you received the wrong impeller. The smaller ID impeller was used on early Force engines and is about 1/16 to 1/8 inch shorter than the impeller for the Mercury designed water pump. Using a shorter impeller in the Mercury designed pump will prevent sealing of the top and bottom surfaces and the pump simply will not suck water and prime itself.

 

[shovelheadnc66]

You know I didn't even think about the height of the impellar I'll have to compare the two. I just figured as long as the vein tips made good contact with the housing it would be fine.