Reply to "Swirl + Surge tanks, vs. just swirl"

An expansion tank is a recovery tank that operates under pressure. Some european manufacturers like to recover coolant this way (under pressure) instead of in an un-pressurized recovery tank. Otherwise the two tanks perform the same function. As the coolant heats up & expands the volume of the coolant eventually exceeds the volume of the cooling system and the excess is relieved by the radiator cap & flows into the "expansion tank" or "recovery tank". As the coolant cools off it contracts, the excess coolant that had been relieved into the "expansion tank" or "recovery tank" flows back into the cooling system via a small valve in the radiator cap.

Removal of the expansion tank and dumping coolant on the ground has two problems:

(1) When the coolant in the cooling system cools and contracts it won't have a recovery tank to refill itself from, so it will draw in air instead. That air will eventually collect in the radiator and create over-heating problems.

(2) Coolant is sweet, it tastes like cool-aid. Any coolant you spill on the ground is liable to be lapped up by animals and it will kill them.

As Dave pointed out, for your cooling system to draw coolant out of the expansion tank you need a radiator cap with the little inner check valve that allows coolant to return from the expansion tank, I'd be surprised if your car's radiator cap didn't have this valve. The pressure rating of the cap on the expansion tank should be a few psi higher than the pressure rating of the cap on the swirl pot (system tank).

-G