water pump mystery

[chucky07]

I've searched past posts and found alot about the waterpumps ..but I'm still very confused. Today as I am reassembling parts onto my new engine..i came across a small problem.. My old water pump has differences from the new one I got from Napa..and until I'm sure it's the right pump I do not want to install it.

In the pic I have the old one next to the new one. Here are the differences:

The old water pump has a hole above the water tube to the right that is blocked off (metal behind it) and the New water pump has the same hole but it is not blocked off (flows through). The old pump has a hole to the left top of the water tube that goes through..and the New pump has a hole in the same location however it is blocked off.

I've read alot about the bypass ..etc..but I'm still not sure of what's what.

Can someone please tell me if this new pump will work..and what is going on with the holes being blocked etc.....

The new pump is from Napa and the numbers on the box are 55-713.

My truck is a 52 1/2 ton..and it has the original 217 6cyl Truck engine.

Any help would be much appreciated so i can finish re installing my accesories as I'm getting anxious as to crank it up.

Thank You

[grey beard]

Based on your photo, I believe you are good to go - insofar as the w/p plate you show is concerned. Your greatest water pump problem with NAPA will be the issue of internal or external bypass type. I'll try to make this as simple as possible.

When the engine is cold and beginning to get warm, the fan belt is turning the water pump because this is a direct mechanical connection. However, the last thing a cold engine needs is water circulating through the radiator. The thermostat closes the flow from the water pump up to and into the top radiator tank.

But to block off all this water flow from the water pump is not really wanted. What is needed is coolant flow INSIDE the engine - but just inside, and not into the radiator. Here is where the coolant bypass goes to work. The only time the bypass is used is while the engine is cold and warming up, and before the thermostat opens to flow to the radiator. Once the thermostat is open, the bypass is no longer needed or used.

Early MoPar flathead engines used an external bypass of the sort that used a two-inch-long piece of heater hose to connec the water pump with the thermostat housing. You can see this as soon as the hood is opened - it's right out there in the middle eof everything. Around 1951, MoPar flathead motors were chaged to the INTRNAL bypass type. This newer feature did away with the need for the short piece of heater hose and its connection. In its place is a new water passage inside the block, right at the front of the engine, above the water pump, and is visible as a 1/2-inch bump proteuing from the front of the block with a corresponding hump on the cylinder hwad. The new style water passaage required a different head gasket with one extra hole and a "hump" at the front end of the gasket that corresponds to the block and head.

You can use an external pump and hose in an internal engine, or an external pump and hose on the old external bypass engine. Just don't eliminate both on any engine. In other words, they need one or the other but may have both.

External water pumps have a rectangular opening on the top, with two studs that accepts a gasket and an adaptor that has two hose outlets - one toward the thermostat for the short bypass hose and the other for one heater hose connection. Water pumps made for internal bypass engines have only a pipe threaded hole on the top for the heater hose nipple.

Good luck. Hope this makes sense.