bizzare thumping noise in coolant system
Hello all. I am new tto this forum and having a very bizarre problem. I recently had a coolnat leak and had my water pump replaced on my 1997 Ford explorer. I also replaced the heater control valve myself and and worried that somehow I got the hoses mixed up (though I thought I was very careful to keep things straight).
Here is the problem: As the car approaches the temperature that the thermostat opens, it starts thumping in the cooling system. I can feel a pulse in the upper radiator hose. That hose builds pressure and then all of the sudden goes limp. It seems to occur most often when the heater is on (I am not sure yet if it ever occurs with it off). Interestingly the thumping will continue for a few seconds after the car has been shut off. It sounds like a basketball being bounced. I thought it might be an air pocket, but the mechanic says he bleed the system. The temperature also seems to swing wildy up and down. I can drive the car to warm it up and then let it sit in the driveway. The guage will swing up to 1/3 up the guage and then down almost to the C in about 4 minute cycles (maybe the thermostat opening and closing, its about 40 degrees right now).
I have attached a picture of the heather control valve, the rear hoses seems to be right. In the front, the left hose goes to the thermostat area and the right hose goes down towards the bottom of the engine. Does this look right? Can someone with an Explorer look and there's and tell me if this is right.
Could this be the new water pump that they put in or a clogged heater core? Any ideas or solutions to dagnose further would be appreciated.