Cooling System Header Tanks & Swirl Pots, in Motorsport

Here at Merlin we sell a wide variety of coolant header tanks. We frequently get asked why, where and how to install them into the vehicle cooling system.

See - Header Tanks and Swirl Pots

What is a header tank?

The header tank is a term given to any container which holds a “head” of water for the cooling system. Be it aluminium or plastic this container stores water for the vehicle cooling system, similar to how some household heating system water tanks work. A header tank is also a version of expansion tank.

Why do I need one?

Most vehicle cooling systems require some form of header tank for two main reasons. A: it allows a convenient place to fill and store the coolant and B: it allows the cooling system to expand under heat and any overflow and excess coolant to safely circulate. Not all vehicles require a header tank because some have a header tank built into the radiator (usually a large portion of the top of the radiator).

How to install a header tank:

The header tank needs to be situated as high as possible in the engine bay so that the water line in the tank is higher than the radiator. Securing to a bulkhead or cross member is the usual place to fix a header tank. With regards to plumbing, this can be confusing but it is pretty simple as shown below:

In brief and for all the header tanks we sell, the outlet is the bottom pipe, the inlet is the pipe at the top of the body and the overflow is the pipe on the filler neck.

Alternatives

An alternative to using the header tank purely as a storage tank is to use a swirl tank. Our swirl tanks have the added bonus of having a standard neck that accepts a standard size cap. This means you can fill the cooling system from this point too.

What is a swirl tank?

Sometimes called a swirl pot, the idea of these is to remove any air from the cooling system. The coolant enters the swirl tank and due to their design, “swirls” around the outside of the inside wall of the tank. As the coolant is heavier it naturally exits the tank at the base to continue its circulation. This then allows any air or steam to escape up through the centre of the tank and out of the over flow pipe.