What does a coolant recovery tank do?
In simple terms, a coolant recovery tank is a reservoir designed to collect hot coolant from the
radiator as the coolant expands. Once the engine shuts down and the coolant in the radiator contracts, vacuum developed in the radiator draws coolant back into the radiator so it’s full at all times.
The confusion about whether coolant expands
Despite what other “experts” have stated, engine coolant does in deed expand as it heats up—all liquids do. The people who say water doesn’t expand as it heats really don’t understand the unique thermal properties of water (engine coolant is approximately 50% water). They assume that since water expands as it freezes that it can’t possibly also expand as it heats. They’ve heard that water reacts the opposite way of all other liquids. That’s not really true.
Water is a truly a unique liquid. It expands when heated and contracts when cold—but not at all temperatures. Water behaves oddly between 40°F and 32°F. As water cools from 40°F to 32°F (freezing) it expands as the water molecules crystalize and turns into ice. As the ice warms from freezing 32°F to 40°F, it shrinks. Above 40°F it acts like all other liquids and expands with as it heats.
Two types of coolant recovery tanks; pressurized and un-pressurized
Traditional radiators use a radiator cap that holds pressure until it reaches its preset pressure threshold. Once cooling system pressure exceeds the cap rating, the cap releases coolant until pressure falls to less than the cap rating. In older vehicles without a coolant recovery tank, the excess coolant gets dumped onto the pavement and is lost forever. So the next time the engine starts with cold coolant, the coolant level in the radiator is low. Car makers weren’t concerned about the low level because the remaining coolant would expand to fill the entire radiator once the engine warmed again.
As car makers moved to more aerodynamic body styles with swept hood designs, they were forced to change radiator types from the traditional down-flow radiators to a cross flow design. The down flow radiators were simply too tall to fit the modern swept hood designs. Cross flow radiators have a much lower height profile but are wider to provide adequate cooling.
At the same time, car makers started installing more 4-cylinder engines to improve fleet mileage ratings. Car makers also decreased cooling system capacities to speed up warm up times; again to improve mileage ratings. That’s because a cold engine requires a much richer fuel mixture. The faster the engine can get up to operating temperature, the less fuel it uses. One way to speed up the process is to reduce the overall cooling system capacity so the engine is heating less coolant. Then, to keep the engine from overheating during driving, the cooling system circulates the coolant at a slightly faster rate and uses multi-speed radiator fans to remove more heat at the radiator. The end result is that newer cars contain less coolant.
Car makers add a coolant recover tank and a new radiator cap
To keep the radiator full at all times and eliminate the loss of coolant, car makers developed
a new radiator cap and installed a coolant recover tank. The radiator cap operates just like the older versions to open and bleed off excess coolant. But instead of expelling the coolant onto the ground, the drain tube flow the coolant into a recovery bottle/tank. So far, the cap operates just like the previous caps. However, as the engine cools and the coolant contracts, it creates a vacuum inside the radiator. A vent mechanism in the cap allows the vacuum to draw coolant back into the radiator from the recovery tank.
The recovery tank in these vehicles are simply storage containers. They are not under pressure at any time. The tank closure is simply a plastic snap lid to allow the user to replenish coolant if needed. The tank also contained COLD and HOT markings so the user can keep the coolant at the proper level.
Body style changes cause cooling system changes
As car makers moved to transverse mount engines and swept hood designs they faced and an under hood space problem. One way to gain more space was to move the radiator forward.
Unfortunately, that limited access to the radiator cap. So car makers decided to move the radiator cap from the radiator to the recovery tank. In this design, the radiator, upper radiator hose, drain hose and recovery tank are all under pressure. The recovery tank is a much sturdier design and can handle more than 15-psi. The coolant tank cap once again acts
like the older design, venting excess coolant to a drain line that empties onto the pavement. However, it has no return vent.
This recovery tank is usually mounted higher than the top of the radiator so it gravity feeds coolant back to the radiator as the coolant cools and contracts. If the tank were mounted lower than the radiator, it would siphon coolant from the radiator.
Why goes wrong with coolant recovery tanks?
Both the non-pressurized and pressurized tanks can develop leaks along the seams. The leaks are most noticeable when the coolant is hot. So you may face a condition where you refill the coolant reservoir, drive the vehicle. Then, when the vehicle cools down you notice it’s low on coolant with no indication of a leak at the tank. One way to confirm a tank leak is to wrap a paper towel around the tank and check it for wetness when you stop.
How to replace a coolant recovery tank
Since pressurized recovery tanks are positioned in the engine compartment above the radiator, removing and replacing the tanks is fairly easy. Simply disconnect the drain line, remove the retaining bolts and swap in the new tank.
Un-pressurized tanks can be a bit more challenging since car makers often hide them inside the wheel well. In those cases, simply remove the wheel well liner to gain access to the tank mounting bolts.
Where to buy a coolant recovery tank
Recovery tank leaks are fairly common on older vehicles, so common that several aftermarket suppliers now offer replacement tanks at a fraction of the price of the dealer. In addition, many of the aftermarket tanks include improvements to prevent repeat failures. So you’re better off buying an aftermarket tank rather than a used tank from a junk yard, since the junk yard part will most likely fail like in the same way as the original. Search aftermarket sellers like rockauto.com for a replacement tank.
Replacement coolant recovery tank cost
A genuine GM replacement recovery tank for a 2010 Buick LUCERNE costs $88.68 from the dealer. An aftermarket replacement tank from rockauto.com costs $33.79. The labor guide shows 0.6 hours to replace the tank. With parts markup and a labor rate of $100/hr, coolant recovery tank cost should run about $200.
©, 2017 Rick Muscoplat
Posted on by Rick Muscoplat