Radiator cap and reservoir tank
The radiator cap is a pressure release valve that is set at 15 psi in cars. When the cooling system fluid is heated it expands and causes pressure build up. The pressure escapes through the cap. The cap string setting determines the maximum pressure the cooling system can hold.
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Increase in pressure opens up the valve. The coolant flows out of the cooling system via the overflow tube to the overflow tank when the pressure is high. The arrangements prevent air penetration into the system. When the radiator cools, it creates a vacuum. The cooling system opens another valve that sucks the coolant resulting into flow back from the reservoir tank.
A coolant absorbs heat generated in the engine. It operates under a vacuum effect where pressure increase allows excess coolant into the overflow tank and back to the radiator when the the pressure reduces.
How it Works
The engine operation produces a lot of heat. However, these engines are designed to work efficiently in a certain range. The work of the cooling system is to keep the engine temperature within this range for fuel efficiency and maximum performance. When the pressure in the cooling system surpasses the specified psi rate, a pressure cap allows the coolant to flow into the overflow tank using a spring-loaded valve. The valve closes to reduce pressure once enough coolant has been released from the system. This process allows the system to operate within suitable psi when the engine is running.
What happens when the engine is turned off? The engine cools and pressure reduces. The pressure cap uses the spring loaded spring to allow coolant to flow back from the overflow tank to the system. This second valve pulls the coolant from the reservoir to fill the vacuum created by the pressure drop in the system.
Basically, the pressure cap keeps the cooling system at high psi and increases the coolant boiling point. It, therefore, allows coolant to absorb more heat from the engine. The radiator cap allows excess coolant to flow to the overflow tank when the pressure is high and to flow back to the radiator when the pressure reduces. If your car engine is performing optimally, there is no need to use high psi cap. Higher psi is only ideal in some situations.
Symptoms of the bad radiator overflow tank:
- Rust formation
- Coolant Leak
- Coolant Smell
- Engine overheating
- Low coolant level
You can always inspect your radiator cap on your own using a radiator pressure tester. If this is too much a task to handle it is advisable contact a technician if you detect a problem in your pressure cap or reservoir tank.
Read more about your car’s radiator: