Why the low coolant light go out after bringing to proper level in 2001 Monte Carlo 3.4 V6 engine?

The low coolant light in your 2001 Monte Carlo 3.4L V6 goes out after you bring the coolant level to the proper level because the sensor that triggers the light is simply detecting the coolant level in the overflow reservoir (or expansion tank). It's a simple float switch or a level sensor that activates when the coolant level drops below a certain point. Once you add coolant and the level rises above the sensor's threshold, the light turns off.

However, this doesn't mean the underlying problem is solved. The reason your coolant level was low in the first place needs to be addressed. The light going out only indicates the *symptom* (low coolant) has been temporarily fixed, not the *cause*.

Possible causes for low coolant include:

* Leak in the cooling system: This is the most common reason. Leaks can be small and hard to spot, occurring in hoses, the radiator, the water pump, the head gasket, or even the engine block itself. Look carefully for any signs of coolant leaks (wet spots, white residue). A pressure test at a mechanic is usually necessary to find small leaks.

* Head gasket failure: A blown head gasket can allow coolant to leak into the cylinders or oil, leading to low coolant levels and potentially other serious engine problems (like white smoke from the exhaust, milky oil, overheating).

* Radiator cap failure: A faulty radiator cap can prevent the system from maintaining proper pressure, leading to boiling over and coolant loss.

* Water pump failure: A failing water pump may not circulate coolant effectively, causing overheating and eventually leading to leaks.

Simply topping off the coolant is only a temporary fix. You absolutely must investigate the *cause* of the low coolant to prevent engine damage. Ignoring the problem could lead to overheating, engine failure, and expensive repairs. Take your Monte Carlo to a mechanic to diagnose and repair the leak.