OK I did a coolant flush on my 2001 four months ago along with a new radiator, recently I've been noticing bubbles in my overflow tank when I revv the engine, I replaced the read cap with one from autozone, and still bubbles, the car does not overheat what could be the problem?

 

either theres alot of trapped air thats making its way out still or your headgasket is blown and youre getting combustion gas in the rad. the bubbles in the overflow tank is the combustion gas opening your rad cap and making its way out

if you changed the coolant 4 months ago and theres still air, i would bet headgasket. best to get a kit to test it. not overheating, but bubbles when you rev are a sign of a early failing HG. had the same thing on my Crown

 

Did you do a new radiator because the old one went out and the car over-heated?

 

The car has never overheated, I replaced the radiator because the old one was clogged and and started leaking in the aluminum part of the radiator, but the car temp was normal the whole time, the bubbling is not always, its only sometimes. What do you think it could be
The car doesn't have any head gasket symptoms

 

When the engine is cold, remove the radiator cap and check the coolant level in the radiator. It should be completely full.

If it isn't and you have coolant in the reservoir tank, you have a leak somewhere.

I find it amazing that you would have air pockets in the engine left over from changing the radiator 4 months ago. As such, I think you may have a blown head gasket. Get a pressurized leak down test performed on your car and find out.

 

when a headgasket fails early, you have no symptoms. on my Crown, i never burnt any coolant in the city, no milky oil, no smoke out of the exhaust, nothing. only on the highway would it push combustion gas into the cooling system and flood my coolant reservoir. the headgasket was just going bad, it would pass a combustion gas test at idle but fail if revved above 4000rpm. because i caught it so early, i only had to replace the gasket. nothing warped or overheated

if you incorrectly bleed a vehicle, over time the air should eventually make its way to the radiator and get pushed into the coolant reservoir. i cant see alot of air making its way out 4 months later