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). For example, if you drive any Subaru turbo model, take a look at your factory expansion tank. As the pressure from the hot coolant builds and exceeds the rating of the radiator cap, it will compress the larger spring to expose the overflow port. 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. I knew there had to be a way for the coolant to get from the tank BACK INTO the radiator. Once the driver parks the vehicle and tur… Aluminum tanks provide the peace of mind that your expanding coolant isn’t just dumping all over the roadway, but is instead keeping your engine at the appropriate temperature. Pingback: Cooling System Tech: Overflow Tanks vs. Free delivery and returns on eBay Plus items for Plus members. An aluminum coolant tank is better suited to deal with the consistent and drastic temperature changes. Get the best deals on Aftermarket Branded Overflow Tanks Radiators. Save my name, email, and website in this browser for the next time I comment. Expansion Tank s Expansion tanks are a little more complex. As temperatures and pressures increase, the expansion tank allows the cooling system to expand without bleeding any off to the atmosphere.  With this type of system, if the radiator has a cap it will be a non-vented cap; the expansion tank will have the vented cap in case the pressure exceeds the expansion tank’s capacity. This lower pressure creates a vacuum and pulls the coolant from the overflow tank back into the cooling system via the small valve inside of the radiator cap. This was good for radiators, and much better for our environment. If an expansion tank is overfilled it will discharge coolant when the system is at operating temperature. Understanding the difference between the functions of both overflow and expansion tanks is helpful for perfecting the cooling system on any build, as well as knowing when you need to run both. In a situation where a large enough tank isn't available a recovery tank can be An overflow tank can also be referred to as a recovery tank and is the simpler system of the two. 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. Once the system balances out, you should not have to add additional coolant. The best way to determine if your vehicle is using an overflow tank would be to find out if your radiator is sporting a pressure rated cap, since this is what determines when the coolant starts flowing between the cooling system and the tank. Aluminum Coolant Expansion Tank fits Subaru WRX 2002–2007 / STI 2004–2016 Price: $231.00 (Incl. An expansion tank is designed so there is space in the tank for the coolant to expand. Expansion tanks are an improvement over overflow bottles in that they do allow the expelled coolant to return to the main cooling system as temperatures decrease. The smaller spring that can’t be seen is how coolant is returned – through the center of the cap. On page 6K-1 it describes the inner workings of the radiator cap. A stained coolant tank is not really a great look for those of you trying to keep a clean engine bay. Aluminum coolant overflow tank are great way to improve coolant capacity for vehicles requires more cooling. For this reason, overflow tanks/reservoirs,recovery tanks have their own vent. Went back to the trusty '69 Chevy Service Manual and VIOLA! Expansion Tank s Expansion tanks are a little more complex. But where an expansion tank really differs is that it is typically a sealed system, not affected by atmospheric pressure. Expelled coolant will enter the tank from the bottom, and when the level rises it will expel through the vent tube. Expansion tanks work in much the same manner as the overflow tank, but server a very different purpose. This system also relies heavily on the pressure created by the expanding coolant. 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). Here the pressure released from the hot coolant fills the top half of the tank and acts as a force to push the coolant back into the system. When it comes to coolant specifically, it also creates steam and gas pressure that needs somewhere to go. Lisa from Flex-a-lite explains the difference between an expansion tank, and an overflow tank. As environmental restrictions tightened, manufacturers had to develop ways to keep the byproducts of the internal combustion and cooling chemicals inside of the car. But try to maintain a good coolant level by adding a similar amount of straight coolant the next time you add liquid to the system. The overflow tank is also commonly referred to as an expansion tank, a coolant reservoir or an overflow canister. This article originally appeared at Mishimoto’s tech blog. In this case, a catch can or overflow can be used with the expansion tank to recapture expelled coolant. This lower pressure creates a vacuum and pulls the coolant from the overflow tank back into the cooling system via the small valve inside of the radiator cap. Just dribbling coolant and blow-by all across the roadways. Note that the cap has a large spring underneath with a small tab in the center. A system with an overflow will have a vented radiator cap, and usually a sealed reservoir cap. 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