Canton Racing Blog has put together some great tips for helping you wrench. We are going to highlight their article on stting up your cooling system and the differences between expansion and recovery tanks. If you are familiar at all with cooling set ups you are probably aware of water cooled and air cooled systems.
An expansion tank is part of the pressurized section of the coolant system. An expansion tank can easily be recognized by the neck and cap used. Since the tank is under pressure it will require a pressure rated cap and neck, (Shown right). The pressure relief in the expansion tank should be the highest point in your coolant system.
An expansion tank is designed so there is space in the tank for the coolant to expand. If an expansion tank is overfilled it will discharge coolant when the system is at operating temperature.
An expansion tank can also be used as a fill point for the system. When an expansion tank is used the radiator doesn’t require a pressure relieving cap. The expansion tanks cap will perform the duties that the cap on the radiator traditionally did. Increasing the capacity of the system and providing a more convenient fill point are among some of the benefits of an expansion tank.
Recovery/Reservoir Tank Set Up:
In contrast, a recovery/reservoir tank typically features a vented cap and is not required to be above the cylinder heads. The job of the recovery/reservoir tank is to hold the coolant that is discharged from the systems pressure relief when the coolant is hot and expanding. When the system cools, the cooling affect creates a vacuum that pulls this coolant back into the system.
A coolant recovery/reservoir tank gives the system the ability to discharge and recharge coolant when needed to maintain the appropriate pressure. This allows the system to maintaining full coolant capacity at all times.
A recovery/reservoir tank can be used in conjunction with an expansion tank or can be plumbed off of a radiator that features a pressure relief.
A recovery/reservoir tank should not be confused with a catch tank however. A recovery/reservoir tank will either be plumbed at the bottom of the tank or have a hose internally that runs to the bottom so coolant can be drawn back into the system. A catch tank, on the other hand, usually features plumbing into the top of the tank and does not have a hose that goes to the bottom. A catch tank serves to collect expelled coolant to be drained from that tank at a later point. While both a recovery/reservoir tank and a catch tank hold excess coolant, a recovery/reservoir will automatically put the coolant back in the system, where as a catch tank will hold the coolant until it can be emptied.