Shop Talk: About Engine Coolant

zerex coolant

Almost every car engine built in the last twenty years is “water-cooled”, which means they regulate their engine’s temperatures by circulating cool water through the engine, and then the radiator, where that water is cooled back down. That water is always inside the engine, rain or shine- and, in extreme weather, that can be a problem. If water freezes inside an engine, it can cause serious damage and may even crack or split the engine block. If water boils inside an engine, it can cause the engine to overheat and lead to serious damage. That’s why coolant (or, antifreeze) is critically important to your car’s performance.

Automotive engine coolant is primarily made up of a compound called ethylene glycol that, when mixed with water, lowers its freezing point and raises its boiling point. That’s the first 90% …

What Engine Coolant is Made Of

Valvoline - How Coolant Works

… the remaining 10% of coolant is made up of a balance of additives that include corrosion inhibitors, pH modifiers, scale inhibitors, buffers, de-foaming agents, and bitter-tasting chemicals that keep young kids and pets from drinking it.

To be considered effective, engine coolant should be able to withstand freezing to a temperature of -36 ℃ and keep from boiling up to 128 ℃. Most coolants can handle those temperature extremes easily. Over time, however, contaminants like rust and scale can build up in the cooling system. Those contaminants can darken and discolor the coolant, and reduce its ability to effectively protect an engine from freezing or overheating. When that happens, you have to change the coolant.

Changing an car’s coolant isn’t as straightforward as changing its oil. That’s because simply draining the coolant from the bottom of the radiator will only remove about 40-45% of the coolant in the system. It’s not enough to “drain and fill” coolant, in other words- the old coolant needs to be flushed from the system.

At my Volvo dealership, we use a special machine (Flushinator?) that keeps the system sealed during the process of removing the old coolant, cleaning the system with detergents and moisturizers that keep the seals and hoses from cracking and leaking, then refilling the car with a precisely measured amount of the correct coolant. There is always a DIY option, of course, but bleeding the cooling system (the process of removing any air bubbles that can form in the many nooks and crannies of a car’s engine bay) can make a DIY option prohibitively difficult. Even trained mechanics can- and do!- often get it wrong when the correct equipment isn’t used. Regardless of what path you choose, though, the main point is this: the coolant in your car is super important.

You can find out more about what kind of coolant is right for your car by checking your owner’s manual for brand compatibility and warranty information and Original Equipment Manufacturer (OEM) recommended coolant, check out this Valvoline/Zerex information guide, below, or- obviously- leave me a comment at the bottom of this post!

Valvoline Zerex Coolant Guide

Zerex Coolant Info

Sources | Images: Popular Mechanics, Valvoline, Wikipedia.


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