I'm replacing my water pump on a 1972 Ford 351C-4V with a Flowkooler and Robertshaw thermostat. The existing pump and replacement pump has a threaded connection next to the heater hose for what almost looks like a vacuum distribution outlet that would be found on an intake manifold, with three connections. Two of the connections are connected together with a loop of small-diameter vacuum hose, and the other has a small-diameter vacuum hose that just hangs there and is not connected to anything. Any idea what this distribution outlet is for or what it does? Seems kind of meaningless with two outlets connected together and the third with a hose that just hangs there.
Originally these went to the intake vacuum and the dual diapraghm on your distributor. It's to retard the spark advance until the engine comes up to running temp.
But it's on the waterpump, not the intake manifold. Would the waterpump create such vacuum? Since it communicates with the vanes of the pump, it appears that coolant would flow through it.
It's a temperature controlled vacuum switch. The water pump has nothing to do with creating vacuum. One of the hoses goes to a vacuum port on the intake.
To clarify a little further, the vacuum can on the OE distributor can either retard the timing or advance it. In a non-smogged engine, you'd only want to add vacuum advance to your base timing, so the vacuum source would be connected straight to the can. But for emissions control the engineers wanted to retard the base timing on a cold engine, then switch over to normal vacuum advance at operating temperatures. So they used this switch you're talking about, which is shaped like a 3-legged "F." One leg connects to a vacuum source. One connects to the retard side of the vacuum can, and the third one connects to the advance side. Inside the "F" is an air valve, which selects which side of the can will be exposed to vacuum. With a cold engine, the retard side is selected. When the engine warms up, the valve moves to close the retard side and open the connnection to the advance side.
What you observed on your engine, I'm guessing, is that a previous owner wanted to disconnect the vacuum can entirely, but felt uneasy to leave the two connectors open. So he/she connected them with the loop that you observed. Somewhere along the line the hose to the vacuum source came loose, so that explains the hose not connected to anything. Or it could be some other variation on this theme. The thing is, to disable all that needed to be done was to disconnect the vacuum source and plug it with one of those little neoprene caps. As it stands now, it sounds like you've got a vacuum leak, which will allow unfiltered air into the engine, and will also lean out the mixture, potentially causing rough running, pre-ignition, and damage to the pistons.
So I would definitely look around for a vacuum source not connected to anything and connect it to the advance side of the vacuum can.
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