Can be the thermostat which is cheap to replace, or it might be the head gasket which is expensive.
replace your radiator cap...
The water in the reservoir of your car may boil out due to a few reasons such as a malfunctioning radiator cap, a leak in the cooling system, or overheating of the engine. It is important to check for any leaks, ensure proper functioning of the radiator cap, and maintain the cooling system to prevent this issue.
Low coolant, inoperative radiator fans, stuck thermostat, failed water pump, restricted radiator, head/headgasket.
A radiator may boil over in a minute due to low coolant levels, a malfunctioning thermostat, a clogged radiator, or a faulty water pump. When coolant cannot circulate properly or regulate the engine temperature, it can quickly lead to overheating and boiling over.
It could be low on water and stuff, fill it.
Engine overheated. Possible causes are: Thermostat stuck closed. Low of coolant. Defective radiator cap. Clogged radiator. Defective Water Pump.
When the radiator cap is removed, the pressure inside the radiator is released suddenly, causing the water to boil explosively due to the rapid decrease in pressure. The water in the radiator is under pressure to raise its boiling point, and when that pressure is suddenly relieved, the water can boil and turn to steam very quickly, leading to an explosive release of steam and hot water.
Excess pressure is building up in the radiator probably from a blown head gasket and is exiting through the radiator cap and into the overflow bottle.
Engine coolant temperature is cooled by the radiator, moved by a water pump and controlled by a thermostat. If there are troubles with any of those components the coolant will boil Also if the head gasket goes bad gasses from combustion inside the engine will get into the coolant and cause it to boil.
A Cracked reservoir Cap would in most cases cause your car to over heat. After your car has ran a while, and built up pressure it would begin to loose water in the form of steam. Once your car is parked and shut off it will then begin to loose water. Once parked your car looses compression which causes the water to boil instead of steam. You would then loose water at a faster rate emptying your radiator and causing your car to run hot.
You need a new radiator cap, you know that silver cap where you put the water into. The spring on the one you have is no good and is letting pressure from the water lines in the motor escape into the water reservoir hence the bubbling noise. Had the same problem and thought my car was heating up, but it turned out to be just that little cap problem.
All auto cooling systems are pressurized. The radiator cap holds the pressure in the system at about 15Lbs. The reason for it is it causes the boiling point of water to be at a higher temperature so the water doesn't boil away as easily. The big white tank beside the radiator allows boiled water STEAM to stay in the cooling system and condense back to water and return back into the radiator as it cools. Champ390