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 contonie 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 thendown almost to the Cin 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?

Could this be the new water pump that they put in or a clog heater core? Any ideas or solutions to dagnose further would be appreciated.

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Are YOU surethe cooling system is topped off properly? If the overflow tank is empty when cold, then you probably have air in your system. This will cause a swinging gauge. When the vehicle is completely cooled down. Pop the radiator cap off and ensure the radiator is completely full. After verifying that the radiator is full, top offthe overflow tank to the FULL COLD mark. Use a minimumof a 50/50 coolant/water mix. Drive the vehicle for an hour or so with the heater on HOT to let the coolant burp all of the air out of the system. Any air in the system will be replaced by the coolant in the overflow tank as the engine cools down. Re-verify both levels in the morning. The radiator should be full to the top and the overflow tank at the FULL COLD mark for a properly topped off cooling system. This should eliminate your fluctuating gauge and

 

There is no doubt that you have air in the system. This one must have a vacuum pulled on the system and then refilled by the same procedure.

 

I have the same problem. How would a person “have a vacuum pulled on the system� ?

 

I have the same problem. Two weeks with a full radiator and expansion tank and the air still wont purge. Sounds like its in the heater core. even thumps for a bit after turning the engine off. How do I get the air out?

 

Some shops have a vac/lift tool to remove the air from the system and refill with the same tool. I have one in my tool box. They cost about 100 dollars, so don't think everyone has one. Most of your busier independent shops should have on. Ask around and see if you see to know what you are talking about. If they tell you that you don't really need one to fix that problem, walk away.