Head Gasket ?

Well the cooling system is pressurized so if you're opening the rad cap when the cooling system is hot (or even just warm) it'll spill out. Hotter it is, the more it'll spray.

 

The system is pressurized. Look at the top of your radiator cap. It will have pounds listed on it. For example lets say its 13lbs, it will hold 13psi , when it goes over 13psi it will come out the overflow tube. A sign of a bad head gasket would be, your pushing coolant out on the ground through the overflow tube, and having to continuously add coolant.

 

Still pressurized.

 

Sounds normal

 

What kind of engine?

Does it have EGR? That's the most common source of excessive pressure if the engine has EGR. Do you see bubbles in the recovery tank when the engine is running?

Are you loosing any coolant?

Take an oil sample and check for coolant products (sodium and potassium) in the oil.

 

Is the engine hot or cold when you’re taking the cap off.

 

Do a fluid test and see if it changes colors. Harbor Freight sells a kit to do it.