1998 Ranger Engine Coolant System Problem

I have a 1998 Ford Ranger with a 3.0 liter V6. 200k miles. The radiator developed a leak and the truck ran hot while I was making it home. I replaced the radiator, radiator cap, and top hose (the bottom hose was replaced about a year ago). I flushed the cooling system with Prestone flush and refilled it. When I refilled it I did my best to make sure I got all of the air out of the system.

Now; When I check it in the morning and the engine has cooled off from driving it the day before, the overflow reservoir is full to the top and the coolant level in the radiator is low. I can top off the radiator and drain down the overflow reservoir, but the next day I find that the reservoir has filled back up and the radiator is low.

Next, I replaced the thermostat and the radiator cap (again). This did not fix my problem. The reservoir still over flows and the coolant level in the radiator still drops low.

Any thoughts? did u use the right radiator cap? spec for this engine is 16 psi.

u could still have some air trapped in the system. with the engine cold take the radiator cap off. start the engine and turn the heater control on and temp control to full hot. let the engine warm up til the thermostat opens and coolant starts circulating. then rev the engine a few times for a couple minutes. any air in the system should make its way to the radiator and burp out the filler neck, along with some coolant. top it off and see if that helps.

if not, the only other thing i can think of is that when it overheated it may of blown a head gasket. best way to check this is to pick up a 'block test kit' at a parts store and follow the instructions. this will tell if theres combustion gas in the coolant, if so theres a head or head gasket problem.
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