2000 Daewoo Nubira Coolant is boiling and gushes all out of

Engine Cooling problem
2000 Daewoo Nubira 4 cyl Automatic 94,000 miles

The only way to add coolant to this car is through the expansion tank.

So I add the correct amount of 50/50 and after minutes of driving it starts boiling in the expansion tank and it gushes out of the tightly closed cap.

There appears to be no leaks, crack, or holes in the tank or hoses.

I've let my car cool down and filled it back up with coolant, drove it and it happens again and again.

The temperature reads normal when driving the car, just sits at the middle, never higher.

I've read all around and everyone says it could be a bad Thermostat, Broken Water Pump, or a Clogged Radiator.

Everyone also suggests to get it pressure tested.

I just bought this car, and it runs perfect, the fans turn on, and the a/c is ice cold. The previous owner had just gotten the heads done.

How can I make sure the heads aren't blown. What do I look for, and what can prove that the heads and engine is just fine.

I checked my oil and it doesn't look like a milkshake, its dark and normal looking.

When the coolant boils, it gushes all out of the reservoir tank and empties all out. I also noticed very little steam coming from the place where you check your oil.

Did I get ripped off?
Or is this an easy fix?

Thanks alot