What is the purpose of overflow tank?

The purpose of the radiator coolant overflow tank is to store excess coolant that is released from the radiator due to pressure build up from heat. It works similar to an expansion tank on a water heater. As you may know, an engine that is working very hard will heat up very quickly.

What size overflow tank do I need?

The general rule of thumb for proper capacity of expansion is 12% of total coolant volume for draw down and 6% of the total volume for thermal expansion. Drawdown capacity is the amount of coolant that can be lost before air reaches the water pump and is introduced into the system.

Are coolant overflow tanks vented?

A system with an overflow will have a vented radiator cap, and usually a sealed reservoir cap. The reservoir is never under steam pressure, which allows the coolant to return via atmospheric pressure.

What happens if you put too much coolant in the overflow tank?

Coolant expands as it heats and contracts when it cools. The extra space prevents damage to your engine and hoses. In worst case scenarios, overfilling your antifreeze tank can lead to electrical damage if overflow comes into contact with engine wiring.

Do you fill the radiator or the reservoir?

On all vehicles that have a reservoir you add it to the reservoir, unless it is totally empty, then you can add it to the radiator directly. Once the radiator is full you will want to finish topping it off through the reservoir. If you just need to add because it is loww, then always use the reservoir.

Do you need a coolant expansion tank?

When the radiator is high enough to act as a fill point and pressure relief an expansion tank is not necessarily required. In those applications a recovery style tank may be used instead. Liquid cooled systems are pressurized in order to raise the boiling point of the coolant.

Why is my coolant expansion tank overflowing?

Coolant, or antifreeze, is essential to regulating the temperature of your vehicle. It’s also extremely toxic and designed to stay inside a closed system. If you’re seeing an overflow, it could be due to a radiator cap, thermostat, water pump, or radiator malfunction.

Do I need a coolant reservoir?

Coolant reservoirs are required because engines go through cycles of expelling and absorbing coolant as they warm up and cool down. Because the coolant reservoir is part of the cooling system, when it has any issues it can quickly lead to issues with the engine.

Should the coolant reservoir be pressurized?

If you take off the cap when it is very hot, the pressure drops and the water may reach boiling point, spurt out and scald you. The coolant reservoir is vented to the outside and there shouldn’t be any pressure buildup in the reservoir itself.