I have a 1978 Mercury 500, 50 HP 4 Cylinder. The impeller on it was toast so I ordered a new one. The old impeller said 65959 on it and when I went to order a new one, that part number matched up with what was on the site for my serial number. They sent me 12-89983T as a replacement part as my old part number is obsolete. I have confirmed with them that this is the correct part.

When I slide the impeller over the driveshaft it stops about a half inch above the impeller key. I tried to use some grease and it will not go down further. It's not hitting the key. If I flip the impeller over and slide it over the drive shaft, it stops about one whole inch above the key.

Everywhere I look says that this impeller is a direct replacement for my other one, yet it does not fit all the way down to the water pump base.

Any thoughts?

Thanks in advance
Sam

The supersession from your original part number to the new one is correct.
How badly did you fry it?
Did the pump housing damage the drive shaft?
Did the old impeller slide right off?

The old impelled had zero fins left. No damage to drive shaft. In fact I'm rebuilding another Merc right now with the same lower unit. Both impellers are the same and both shot. They both fit both drive shafts but the new one won't fit either.


Old impellers came right off like butter.

Got a serial number?

4965581 is the serial number

Got me man, serial number and part supersession from Merc say the new number is correct.
Try calling Merc direct.

hit the ds w/ some emerycloth. next clean out the impellar key groove and if none of that works hmmm....... throw the impellar in boiling water???.... good luck. o and dont forget to remove the old impellar debris.