could have a crack in it that is leaking under pressure
Hot water (engine coolant) expands and pushes its way back into the coolant reservoir.
There could be several answers to that question. The thermostat could be stuck closed. The reservior could be overfilled. The cooling fan may not be working. The radiator could be stopped up.
Theres to much water in your reservoir bottle, theres a mark were it should be filled up to, any more and it will flow over.
most likely the sensor in the bottom of the coolant reservoir is gone change reservoirs then see
Check the sensor located at the bottom of the reservoir.
A dirty fuel filter is one possibility.
If you want to simply remove the existing coolant and replace it with new, the procedure is very simple. If the cooling system needs to be flushed, do that first and then follow these steps to change coolant. 1. Uncap the coolant reservoir. Open lower drain plug. It is located on the lower edge of the radiator on the driver's side of the vehicle. Turn the plug several times to open the plug fully. It is made of plastic, so be careful when using any tools to turn it. 2. After the coolant has completely drained, close the drain plug. 3. Pour 50/50 water/coolant mix into the coolant reservoir. It will take a while for the reservoir to empty into the engine cooling system. 4. After adding approximately one gallon, start the engine. This will pull more coolant into the system. 5. Continue adding coolant until the level reaches and remains at the "full" level. 6. Cap the coolant reservoir.
Radiator could be plugged or restricted
Either the vent cap is no longer venting, or the reservoir is overserviced. Just a thought.
the coolant temperature sensor is faulty. It will need to be replaced
make sure there's enough coolant in the radiator.
Change the Coolant Temp sensor