![]() ![]() As temperatures and pressures increase, the expansion tank allows the cooling system to expand without bleeding any off to the atmosphere. You’ve seen these on some classic cars, like the Galaxie, or even the old Shelby Cobras.īut where an expansion tank really differs is that it is typically a sealed system, not affected by atmospheric pressure. Expansion tanks are just that: tanks that provide expansion of your cooling system, giving you up to a half gallon more coolant. Expansion tanks work in much the same manner as the overflow tank, but server a very different purpose. Some manufacturers and websites will confuse the overflow reservoir for the expansion tank, but the two perform very different functions. The reservoir is never under steam pressure, which allows the coolant to return via atmospheric pressure. With our overflow tank, the two tubes are different lengths, with the vent being much longer, allowing the level to increase before it vents off excess coolant.Ī system with an overflow will have a vented radiator cap, and usually a sealed reservoir cap. These tanks can be cylindrical, with both hoses attached at the bottom, like ours, or the factory style will enter at the bottom and the vent will be at the top. It allows the expelled coolant to fill the reservoir to a certain point before it’s expelled to the atmosphere (ground). The longest one on the outside is also the longest one on the inside. Expelled coolant will enter the tank from the bottom, and when the level rises it will expel through the vent tube.įrom the bottom of an overflow like ours, you’ll find two tubes. For this reason, overflow tanks/reservoirs,recovery tanks have their own vent. It’s really just a guide, however, filling the reservoir during cold cycles just means that you will likely end up with coolant on the ground. Many plastic tanks have a ‘cold’ and ‘hot’ mark those marks indicate where the coolant should be in the tank during cold cycles (non-running) and hot cycles (engine running). This, in turn, adds more coolant to your system and helps to keep the engine a little cooler. The process of returning coolant back to the radiator is possible because the combination of the reduced steam pressure allows the atmospheric pressure to push coolant from the tank back into the radiator through the vented radiator cap. The smaller spring that can’t be seen is how coolant is returned – through the center of the cap. ![]() The heavy spring on the radiator cap that can be seen is compressed when pressures reach roughly. Different manufacturers called them different things: overflow – to catch the overflow from the radiator reservoir – to store the captured coolant or recovery tank – to recover coolant that was expelled when the pressure increased. This was good for radiators, and much better for our environment. Overflow tanks were added to cooling systems to catch the overflow and store it, instead of leaving it on the ground. Overflow Tank – Also: Reservoir or Recovery Tank Capturing that expelled coolant meant that it could then be recovered and reintroduced back into the radiator. Adding a reservoir to that vent tube allowed the steam to be expelled, but also allowed for the coolant that came with it to be captured instead of being discarded to the ground. This process was good for the radiator, but bad for the environment. But as the steam expands, so does the pressure, and often times the vented cap also expels coolant. When coolant expands from engine temperatures rising, it typically creates steam, and the vented cap allows that steam to vent in order to protect your cooling system. Many vehicles back in the 1960s and earlier had a tube attached to the radiator’s filler neck, and that tube vented to the atmosphere (the ground). Here, we will explain both tanks and hopefully clear up any confusion about how each is used. While the names are fairly self-explanatory, and both perform similar functions, there is a difference between the two. We get the question occasionally about expansion tanks and overflow tanks. ![]()
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