Water pump impeller questions

[Mr. K]

Hello:

We were late in winterizing our engine this year due to a cold snap soon after haulout. After running a heater in the engine compartment overnight to defrost things, we ended up getting the engine started, but it wasn't pumping the antifreeze in. So we opened the water pump cover and saw the impeller was in pieces.

We had great difficulties in getting the old impeller off. We ended up cutting it away, taking the circlip out, and then we had to pry, twist and otherwise force the metal ring off the shaft. The spare impeller we have appears to be the right shape, but is too small and looks like it would have to be pressed in to fit.

My questions are:

1) Should the impeller remove and reinstall easily or does it have to be forced on/off?

2) Should the shaft be able to come out of the water pump housing? We were able to pull it out to a point, but it wouldn't come out the rest of the way.

3) DO I need another type of impeller than the one we have? The engine serial number is 198356 and the model number is 5111. The water pump cover says Oberdorfer on it.

4) In the short-term (due to more damage just the impeller) should I be thinking about just putting the pump cover on, filling the engine with antifreeze and waiting till the spring?

5) Any more damage I should be worried about?

Thanks,
Chris Krepski
Ottawa, ON

[Don Moyer]

Chris,

Here are the answers to your questions:

1) Should the impeller remove and reinstall easily or does it have to be forced on/off?

2) Should the shaft be able to come out of the water pump housing? We were able to pull it out to a point, but it wouldn't come out the rest of the way

Changing an impeller with the pump installed on the engine is always a bit problematic, depending almost entirely on how much access you have, or don't have. In the case of Oberdorfer, the shaft should have come out of the pump, which would have made removal of the impeller itself somewhat easier. The fact that your shaft did not come out as you pulled on the impeller suggests that there may be considerable scouring between the shaft and the housing. I recommend that you remove the pump for a more thorough inspection.

3) Do I need another type of impeller than the one we have? The engine serial number is 198356 and the model number is 5111. The water pump cover says Oberdorfer on it.

All Oberdorfer pumps used on the Atomic 4 are either a 202M or a 201M series pump, and both series use the same impeller. The engine mounted pump just aft of the accessory drive is a model 202M, and the belt driven pump in front of the engine on freshwater cooled engines would be a model 201M. The fact that your spare impeller is smaller than your Oberdorfer impeller suggests that it's not an impeller for the Oberdorfer pump.

4) In the short-term (due to more damage just the impeller) should I be thinking about just putting the pump cover on, filling the engine with antifreeze and waiting till the spring?

It would be better to repair the pump now, so that you can pump antifreeze through the engine and exhaust system for more effective winterizing. Be sure to check the 90 degree elbow on the discharge of the pump, the "T" fitting in the center of the water jacket side plate, and the thermostat for pieces of impeller.

5) Any more damage I should be worried about?

Depending on how hard the freeze was in your area, I suppose you could worry about a crack on one of your water jackets, although I really consider this to be unlikely this early in the winter.

Regards,

Don