Coolant Reservoir Overflowing

A coolant reservoir that is overflowing can cause serious problems. If your vehicle is a liquid-cooled, traditional engine, it will most likely have a coolant reservoir. A coolant reservoir is a container designed to temporarily store coolant. Coolant expands as it heats up in your vehicle's engines. The coolant will expand and then be transferred to the reservoir. Once it cools, it will contract.

However, there may be problems that cause the coolant reservoir overflow to occur. Some coolant might leak out of the top of your reservoir, rather than returning to the cooling system.

STUCK THERMOSTAT

Your coolant reservoir could overflow if your thermostat is stuck. The thermostat is a temperature-based valve. The thermostat regulates the flow of coolant through it by either allowing or blocking it. This is dependent on the coolant temperature. The thermostat will be opened when the coolant reaches a temperature of around 190 to 200 degrees Fahrenheit.

Sometimes thermostats can get stuck. Coolant can't pass through a vehicle's thermostat if it is closed. Coolant will instead continue to heat up, expanding ahead of the thermostat. The coolant that is left over will enter the coolant reservoir and spill out.

COMBUSTION GAS LAKE

Your coolant reservoir could overflow if combustion gases are allowed to leak into the vehicle's cooling system. Combustion gases should follow an ordered path. Your vehicle's engine will burn air and gases to create combustion gases in the combustion chamber. These combustion gases will then be expelled from the tailpipe into the exhaust system.

A cracked engine block or a blown head gasket can cause combustion gas leaks. A cracked or blown engine block can cause combustion gases to escape from the combustion chamber into the cooling system. The coolant will be pushed into the reservoir as the combustion gases enter the cooling system.

BLOCKED RADIATOR

Even if the thermostat isn't stuck or there are no combustion gas leaks, a blocked radiator could be a problem. Your vehicle's radiator is the most critical piece of equipment. The radiator will heat up as coolant flows through it. After passing through the radiator, the coolant will become cooler.

Radiators can get blocked. For example, rust particles and sediment can build up in the tubes of your radiator. This can cause a backup of coolant. Until the blockage is removed, some coolant could leak out of your reservoir.