- There may not be enough expansion room for the coolant to flow into - If the coolant level in the radiator is too high, it may not have enough space to expand upwards into the overflow bottle so that it can be drawn back into the radiator as it cools down. Check the coolant level in the radiator and make sure it is filled at or below the "Full" mark.
- The overflow bottle cap or hose may be clogged - If either the overflow bottle cap or the hose that connects the overflow bottle to the radiator becomes blocked, the coolant won't be able to flow into the overflow bottle. Check the cap and the hose for any obstructions or damage and clean or replace them if necessary.
- There's a leak in the overflow system - If there is a small leak in the overflow hose, you may see coolant dripping under the car in the area below the overflow bottle and radiator. Check the overflow system for any signs of leaks and repair as needed.
- Water pump failure - A faulty water pump might reduce coolant circulation, leading to overheating in the engine block where the radiator is located while leaving less coolant for the overflow tank.
If you are still having trouble after checking these potential issues, it may be best to take the car to a professional mechanic for further diagnostics.
