These Are The Essential Fluids That Keep Your Car Alive

And there's so, so much more. Like a car's fluids.

From the oil keeping the engine properly lubricated (and even cooled in some designs), to the thin hydraulic fluid coursing to the brakes to reign in the engine's primary job of propulsion. And everything in between. Let's avoid the blinker fluid jokes (though that's actually kind of a thing), and instead, quickly discuss each and every common fluid found in cars today.

We won't outline them from most important to least important (spoiler alert: They're all important!) but will skip detailing what DEF and windshield washing fluid are.

Oil is, for all intents and purposes, the lifeblood of the engine. Its duty is to lubricate the complex system of bearings, seals, and surfaces that keep it running smoothly, especially once it's up to operating temperature. Oil comes in various types (conventional, synthetic, semi-synthetic) and viscosities (5W-20, 10W-40, 0W-20, and so on)—the best way to figure out which is best for your engine is to read your owner's manual. Check out this post for more on viscosities.

Oil also actuates an engine's variable valve timing system, if it's equipped, and lubricates other components like turbochargers.

As far as its maintenance interval, every 3,000-5,000 miles is generally considered the standard. But once again, check your owner's manual. Oil breaks down and loses its effectiveness over time, and will even varnish and cause sludge buildup in the engine if not changed in time. So it's paramount to ensure the stuff that's in there is always doing its job to the best of its ability.

On the opposite end of continued motion is controlling it, which is where brake fluid comes in.

Brake fluid lives in a reservoir, is pressurized by the master cylinder, and reaches the brakes on each wheel via hard and soft lines.

Brake fluid service intervals vary, but there are some simple ways to tell when it's in need of replacement. One is poorer braking performance, usually joined by a longer/spongier brake pedal travel. Another is to open the reservoir and observe its color: healthy fluid has a light straw color. If it's dark brown, or darker, it's time to change it. Another way is to use a simple tester, which analyzes how much moisture has built up in the fluid.

This slippery substance is hygroscopic, meaning it sucks up moisture, which over time reduces its effectiveness. Some important specs to keep in mind about brake fluid is its wet and dry boiling point. Dry means when it's fresh and hasn't had time to absorb moisture, whereas wet means when it has. The standard measure for wet boiling point is when the fluid's water contamination is at 3.7%.

There's DOT 3, DOT 4, or DOT 5 brank fluid, with the main difference being the higher the number, the higher the dry and wet boiling points. Typically, performance and racing applications see DOT 4 and 5 as they both have higher dry and wet boiling points. The latter is actually considered hydrophobic (so, it doesn't like moisture) due to being silicon-based instead of glycol like the others. But it still breaks down and loses effectiveness over time.

When it comes to another vehicular motion, steering, many cars have what's called hydraulic power steering. It's largely given way to electricity, but that doesn't mean it's not still on the road. In fact, both my Audi S4 and BMW 128i have it. The root here is that hydraulic fluid—which is pressurized via a pump attached to the engine—helps you turn the wheel. Without it, steering is a real chore, ask me how I know after I bought a Land Rover Discovery 1 with a disconnected power steering system.

Though, it's not to be confused with hydraulic brake fluid—these aren't interchangeable. Power steering fluid has different ingredients and properties, and also has its own set of specifications. The best way to determine which is best for your car is, yet again, to read your owner's manual, but they're usually pretty general. Such as green power steering fluid (like Pentosin CHF11s and Liqui Moly Central Hydraulic System Oil) being a common spec for European vehicles.

Once again, service intervals vary, but it's usually somewhere around every 50,000 miles. A quick way to check the condition of this fluid is to open the reservoir and pull out a sample with something like a turkey baster, or just read the dipstick: Is it cloudly, murky, dark, brown, or anything other than the color it was when new? If so, it might be a good idea to change it.

Unless you're tooling around in something like an old Porsche or VW, your car is water-cooled, meaning there's a mixture of water and coolant moving around through a series of channels in the engine keeping it at operating temperature. This coolant stays cool by pumping through a series of hoses to the radiator at the front of the car. There's more to it, such as a thermostat that controls its flow, as well as its ability to provide heat to the cabin, but this is the general gist of it.

Coolant mixes with deionized or distilled water, usually at a ratio of 50:50, though warmer climates can run more water for improved cooling. So long as you don't run 80 percent water and then head up to some high-elevation skiing for the weekend. That's because coolants' main jobs are to prevent freezing, lubricate the cooling system, and prevent rust.