How It Works: Vehicle Fluids

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Your vehicle runs on more than just gasoline. It contains numerous fluids, some of which should be regularly checked and changed to keeping it running right for as long as possible.

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Engine Oil

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Oil lubricates parts that are moving thousands of times a minute and with a hair’s worth of clearance between them. It also traps carbon particles caused by combustion, and helps to cool the engine. Change it, and the oil filter, according to the vehicle’s maintenance schedule.

Most auto manufacturers recommend synthetic oil. Virtually all synthetics have a fossil-fuel base, but they go through a synthetic process that creates small, uniformly-sized molecules. Oil also contains detergents, antioxidants, and anti-wear agents. It’s labelled by its viscosity, such as 5W-30 or 10W-40, which indicates how well it flows at a specific temperature. A lower first number means it won’t get too thick in cold weather, while a higher second number means it won’t thin out in the heat. The numbers are standards, not temperatures, and while many people think the W stands for “weight,” it’s actually for “winter.”

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Check the oil level after the engine’s been off for a few minutes. Pull out the engine oil dipstick, wipe it clean, reinsert it, and then pull it out and check the oil level against the marked notches on the stick. If it’s low, add oil through the filler on top of the engine (look in your owner’s manual if you can’t spot it). Add it gradually and keep checking the dipstick. Too much oil is as bad as too little.

Brake Fluid

This hydraulic fluid operates the small pistons that work the brakes. Electric vehicles don’t contain many fluids, but this is one they do: they have regular hydraulic brakes as well as regenerative braking systems. Whatever your vehicle, check your maintenance schedule to see if changing the fluid is recommended.

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The brake fluid reservoir is a clear or opaque plastic container, usually found near the back of the engine. Check the level against the minimum and maximum lines on the side of it. If it’s low, get your vehicle checked: a leak in the brake lines is dangerous.

Be cautious if you have to top up brake fluid. It easily absorbs water, even from humid air, so buy a new bottle if the one you have has been sitting for a while. Clean the top of the reservoir before opening it, so no dirt falls in. Don’t spill the fluid, as it eats paint. And never use anything other than brake fluid. Substituting other fluids will result in a huge repair bill.

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Transmission Fluid

Automatic transmissions, including CVTs, contain lubricating fluid. Check the level with the engine running; pull out the transmission dipstick, clean it, reinsert it, and check the minimum-maximum notches on it. Low fluid usually indicates a leak, so get it to a technician. To top it up in the meantime, use a funnel to pour fresh fluid into the dipstick tube. Many automakers use proprietary fluids, so be sure you’re buying the right stuff for your vehicle. CVTs get CVT-specific fluid, too.

While you’ve got the dipstick out, give it a sniff. If the fluid smells burned, or if it’s dark brown or black, your transmission  needs service. Most automakers recommend changing the fluid as part of maintenance, usually between 70,000 and 100,000 km.

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Coolant

Engines generate so much heat, they’ll damage themselves if they get too low on coolant. It’s commonly called “antifreeze,” but it has to be mixed 50/50 with water so it doesn’t go slushy in cold weather. Some coolant is sold pre-mixed for easier top-ups, but if you have to fill it often, have the system checked for leaks.

If your vehicle has an older-style radiator cap, never open it when the engine is hot. The system is pressurized, and you can be badly scalded. New cars have a coolant reservoir with level markers on the side. Scheduled maintenance will vary by automaker, but it’s a good idea to have the cooling system flushed out and refilled every three to five years, to prevent buildup of rust and sediment. The coolant flows through the heater core, a small radiator that supplies the interior heat. If it clogs up it’ll need replacement, and some are located deep in the dash where it’s very labour-intensive and correspondingly expensive to get to them.

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Windshield Washer Fluid

This system doesn’t need maintenance, but there are a couple of things to know. Nothing will go wrong if you don’t switch between “summer” and “winter” washer fluid, but they’re formulated to better tackle baked-on bugs or caked-on road salt, respectively. Never use plain water. It doesn’t do a very good job, and if it’s still in there in winter, it’ll freeze and cause damage. The coolant and washer fluid reservoirs are close to each other on many cars, so be sure you’re filling the right one. Most other reservoirs have “maximum” levels, but you can fill washer fluid to the top.

Diesel Exhaust Fluid

Known as DEF, this is used with diesel engines to reduce harmful emissions. It doesn’t go into the engine, but is automatically squirted into the exhaust system. The DEF tank  usually needs refilling at the scheduled oil changes, but if it gets low, you’ll get a warning notice in the instrument cluster well in advance. If you let it run dry, the vehicle will either not restart, or it’ll limit your speed. DEF is sold at most gas stations and auto parts stores, and you just pour it in. The filler is usually beside the fuel cap, but on some it may be under the hood.

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Power Steering Fluid

Many automakers are switching to electric power steering, which doesn’t use fluid, but vehicles with hydraulic power steering pumps do. If you’re low on fluid, the steering wheel may be harder to turn, or you’ll hear a squealing noise when you turn the wheel.

The power steering reservoir is usually located at the back of the engine. On most vehicles it’s clear or opaque, so you can check the level with the marker on the side. On older vehicles without a see-through reservoir, take off the reservoir cap, which contains a dipstick in the lid. Low fluid could indicate a leak, so get it checked.

Rear Differential Oil

Rear-wheel or four-wheel-drive vehicles have a rear differential to turn the wheels, which contains gears and is filled with special (and very foul-smelling) oil. As this oil ages, especially in a truck that’s frequently towing or hauling heavy loads, it loses its ability to properly lubricate the gears. Change this oil every 50,000 to 95,000 km, or as recommended in the maintenance schedule.