2001 Kia Sportage water

Removing the thermostat can cause overheating because the hot coolant doesn't stay in the radiator long enough to give up its heat. It can also cause excessive engine wear and emissions if the engine doesn't reach operating temperature.

The first thing you need to look at is if there's steam associated with that bubbling coolant. An engine won't get hot enough to overheat in just a few minutes, so if the coolant appears to be boiling that soon, it's not overheating. The air bubbles are coming from a leaking cylinder head gasket. Your mechanic can perform a chemical test at the radiator to check for combustion gases. If the test is positive, the cylinder head is warped or cracked, and / or the gasket is leaking.