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Stock vs Aftermarket Coolant Reservoirs: When is Your Coolant Reservoir Due for Replacement?

Let’s be honest: while it’s easy to understand the role that radiators play in regulating car and truck engine temperatures, the job that coolant reservoirs perform isn’t always as clear. The fact that they haven’t always been a standard automotive feature, and the wide variety of names they’ve inherited over the years – from overflow bottles to expansion tanks – also hasn’t done much to demystify their purpose.

Coolant reservoirs are a standard part of every modern pressurized cooling system, and regardless of what you call them, they’re just as responsible for preserving the environment as they are for regulating your engine’s temperature. Let’s cut through the terminology surrounding these ubiquitous coolant containers and take a look at what they do, what they’re made of, and how to recognize when yours might need to be replaced.

Time to Beat the Heat With a New Coolant Reservoir

Thermometer and cars driven on the bridge.

Everything begins with the liquid coolant that’s stored in your radiator. It’s the heart of your engine’s cooling system; and when it expands from a cool low-pressure state, to a warmer high-pressure one, it needs someplace to safely expand into. Your system’s plastic coolant reservoir tank is the place where this hot, pressurized coolant goes until, under negative cooling pressure, it’s drawn back into the radiator.

This simple, otherwise imperceptible process takes place every time your engine starts and reaches operating temperature. And in a country like Australia where temperatures soar and opportunities to top off on coolant can be sparse, the benefits of having a properly functioning overflow reservoir are easily quantified by:

· Always having an adequate volume of uncontaminated coolant available in the system;

· Not having to replenish a dangerously pressurized system every time your engine heats up; and,

· Preventing toxic, glycol-based coolant mixtures from being released onto the ground.

As opposed to stopping every few kilometers on hot days to refill your radiator, standard coolant overflow tanks are essential safety components for your cooling system that also happen to be significant cost and time savers. And fortunately, if you’re having a problem with your system’s overflow, you can easily find high quality aftermarket overflows for some of the most popular cars and trucks in Australia.

Superior Quality Overflows for a Range of Popular Australian Models

White Toyota Lancruiser 200 and Nissan Patrol Y62 parked in nature.

Make no mistake: Australia’s wide selection of high quality aftermarket overflow bottle and sensor combinations is due in no small part to the environment. With temperatures in many parts of the country routinely capable of reaching 35°C, taking to the road with a potentially defective coolant overflow container simply isn’t an option.

Superior quality aftermarket overflow tank combinations eliminate that possibility, and you can find tough, OE-fitting reservoirs for a full range of Australia-delivered cars, trucks, and utes online, for models such as:

· Toyota Landcruisers, Hiluxes, and Camrys;

· Nissan Patrols, X-Trails, and D21 and D22 Navaras; and,

· Mitsubishi CE and CJ Lancers, L400s, and Outlanders.

Each of these heavy duty containers is a direct replacement for your vehicle’s OE coolant reservoir overflow, and is built to meet or exceed OE performance. Understanding how they’re constructed, however, is a crucial aspect of grasping just how important these reservoirs are. They have to be able to deliver the best balance of economy and efficiency possible, and not surprisingly that comes down to the choice of materials.

The Benefits of High-Grade Polyethylene Reservoirs

Plastic coolant reservoir tank filled with pink liquid in a car

It shouldn’t come as a surprise that a well constructed coolant overflow tank is more than just a conveniently located container to capture hot coolant. That’s because, although location matters (overflow bottles should always be positioned higher than your radiator), the hot, harsh environment inside an engine compartment means that reservoirs not only have to contend with 90°C liquids, but with ambient temperatures that can also exceed 130°C.

Durable, high-grade polyethylene (PE) is the most common choice for both OE and OE replacement overflow tank construction. From a manufacturer’s perspective, not only does PE allow for quick, large-volume production, but it also offers a variety of inherent benefits that include:

· High moisture and corrosion resistance;

· High initial flexibility and impact strength; and,

· Sufficient colour opacity to allow container contents to be seen easily.

But while PE offers the best balance of all properties for a radiator overflow bottle, the principals of thermal expansion invariably mean that sooner or later every overflow reservoir needs to be replaced. It also means that you need to be on the lookout for early indicators that your coolant overflow bottle could be due for replacement. This is particularly the case if you spend a lot of time off roading, or your make and model of vehicle has a history of overheating due to an insufficiently sized reservoir.

Recognizing When Your Reservoir Needs to Be Replaced

A man standing by overheated car and talking on his phone

There’s no getting around the fact that exposure to heavy, prolonged heating cycles will eventually have an effect on both the condition of your radiator overflow tank, as well as its performance. Everything from air bubbles in the coolant system causing inconsistent cooling, to an OE tank simply being too small for the job, will all contribute to its degradation.

On inspection, the visible signs that your radiator coolant overflow tank is in trouble couldn’t be any clearer:

· Heavy yellowing and discolouring;

· Stress cracks and fissures along overflow bottle seams; and,

· Noticeable brittleness, or broken brackets.

Dirty coolant reservoir tank filled with pink liquid in a car.

In the absence of a “hands-on” reservoir inspection – one that could potentially confirm a lack of coolant in the system – the signs that your reservoir has already begun to fail can be considerably more ominous, and they might include:

· Coolant collecting under your vehicle;

· The sweet smell of coolant inside the vehicle; or,

· Hissing sounds coming from under the bonnet.

While any of these external signs are solid indicators that there’s a problem somewhere in the cooling system, your overflow reservoir tank is the first place you should check for leaks, cracks, or possibly even a defective cap. A failed reservoir is problematic, but it’s still the lesser of a whole list of probable cooling system problems.

It’s important to bear in mind, though, that if your reservoir is indeed cracked or broken, PE isn’t amenable to chemically bonded repairs. Replacing your defective overflow container with a new OE replacement is the only way to be sure that you’ve fixed the overflow problem.

The Final Word

At the end of day, while your radiator is responsible for making sure that your engine always has enough coolant, it’s ultimately the reservoir’s job to ensure that the radiator, in turn, never runs out of coolant. It’s the least glamorous, and most basic component in your cooling system, but it’s also the one that keeps your from having to deal directly with pressurized, scalding hot coolant every few kilometers.

If your car or truck is experiencing persistent, or increasingly regular problems with overheating, a new, heavy duty plastic coolant reservoir tank might be the component you need to fix it. There’s really no mystery at all about what their purpose is; and if yours is ready to be replaced, now’s a great time to do it.