Except for electric vehicles, car ownership goes further than starting the engine and driving it. Cars are complex machines that combine a collection of mechanical systems working in complete harmony. 

With cars’ complex mechanical nature comes maintenance, as most of their mechanical systems have specific fluids you must change to keep it running in top order. 

Our busy lives sometimes get in the way, though, and we forget all about our vehicle's required maintenance. Below, we'll cover all the risks of not changing oils and fluids in accordance with the owner's manual. 

Risks of Not Changing Oil and Fluids

Your vehicle has a wide range of oils and fluids with various purposes, ranging from lubrication to cleaning to maintaining temperatures. Most of these oils and fluids require periodic changes to keep your vehicle running at its best for the long term. 

Here's what you risk by not changing your oil and fluids at the recommended intervals. 

Risks of Not Doing an Oil Change

Your oil is the primary lifeblood of your engine. Without it, the mechanical motion inside your engine would create excessive friction and heat in mere seconds, resulting in catastrophic damage. Basically, the engine would seize up, or the components would break apart. 

As the oil in your engine breaks down, moisture, fuel, and other contaminants dilute it, decreasing its viscosity and impacting its ability to lubricate. It can also develop sludge that can increase friction and stress on the engine's moving components. 

Changing your engine's oil and oil filter at the manufacturer's recommended interval ensures you get fresh motor oil in the engine before oil breaks down enough to cause any damage. 

If you don't change your dirty oil at the automaker's recommended interval, which is generally every three months or 4,800 km to every seven months or 12,000 km, you risk the engine oil losing its ability to lubricate and clean the internal engine components. This can cause additional stress on the internal engine components and lead to excessive engine wear or possible premature failure. 

While full engine failure may take some time to occur, other early symptoms will arise, including tapping or knocking from the car's engine, the engine running rough, and reduced fuel economy. 

Pro Tip: Changing to a synthetic oil doesn't mean you can wait longer or skip oil changes. Yes, synthetic generally has a longer oil life than regular oil, but the manufacturer's recommended oil change interval is based on the engine's tolerances, not the oil you use. 

Risks of Not Changing Automatic Transmission Fluid

Automatic transmission fluid is one of the hardest-working fluids in your vehicle. It's not only responsible for hydraulic pressure in the transmission that allows it to shift gears, but it also provides lubrication, cleans the transmission's internal moving parts, and helps regulate the transmission's internal temperature. 

Most manufacturers recommend changing the transmission fluid and filter — if applicable — every 48,000 to 100,000 km. In some cases, you will need a repair facility to perform a flush using a machine, but other vehicles require you to only remove the transmission pan, drain the fluid, and replace the fluid and filter. 

If you don't replace your transmission fluid, it will break down much like engine oil and lose its lubricating and cleaning properties. This leads to high temperatures, sludge buildup, and excess friction, which can damage the internal clutches that shift the gears.

As the internal clutches wear, the friction and heat will continually increase. After enough time passes, all the friction material on the clutches will wear away, resulting in transmission slippage or failure of other internal components.

Once slippage or internal component failure occurs, a new or rebuilt transmission is the only way to get the vehicle back to normal. 

Risks of Not Changing Manual Transmission Fluid

Unlike automatic transmission fluid, manual transmission fluid doesn't have any hydraulic properties. Instead, its only purpose is to lubricate and clean the internal transmission components. 

Like most oils, manual transmission fluid breaks down over time. It can also become contaminated by outside debris and metal shavings from the transmission's internal components. 

Most manufacturers recommend changing the manual transmission oil every 48,000 to 96,000 km to combat viscosity loss and contamination. 

If you don't change the manual transmission fluid, the thinning viscosity limits its ability to lubricate the transmission's components. This can make it difficult to shift gears and put extra stress on the transmission, potentially causing early failure

Risks of Not Changing Coolant

Coolant's primary job is to regulate the temperature of the engine, but it has other functions too, including: 

  • Acting as an anti-freeze agent to prevent the cooling system from freezing up in the winter
  • Introducing rust-inhibiting additives into the cooling system to prevent rusting
  • Regulating the automatic transmission fluid temperature, which then regulates the transmission's temperature
  • Regulating the temperature of the heater to keep the cabin warm

Most manufacturers recommend replacing the coolant at least every 96,000 km, but the intervals are sometimes as short as 48,000 km. They recommend replacing it at these intervals because this is when the rust inhibitors in the coolant begin breaking down. As they break down, corrosion can start forming in the cooling system and turn the coolant from a liquid to a thick slurry. 

The slurry reduces the coolant's ability to remove heat from the engine and transfer heat to the heating system, potentially causing the vehicle to overheat or the heater to not work properly. 

Eventually, the slurry can become so thick it blocks the veins the coolant passes through or the radiator, causing even more potential overheating issues, which can lead to engine failure. 

Risks of Not Changing Power Steering Fluid

Your car's power steering fluid is responsible for transferring the hydraulic pressure needed to turn your front wheels with minimal effort. Unlike engine oil or transmission fluid, the power steering fluid doesn't keep hot internal components lubricated, so it tends to become contaminated instead of breaking down. 

Not all automakers have recommended power steering fluid change intervals, but those that do generally recommend it every 48,000 to 128,000 km. For those that offer no suggested interval, you can visually inspect the fluid at the 48,000-km mark, then every 16,000 km after that. 

Remove the dipstick from the power steering pump and wipe the fluid on a white cloth to inspect the fluid. Suitable power steering fluid will be a bright red. If it's dark and you can see particles in it, it's time for a power steering system flush. 

Failure to flush contaminated power steering fluid can cause tears in the seals and gaskets in the power steering system and lead to leaks. Also, excessive contamination places stress on the power steering pump, which can cause it to fail. 

Risks of Not Changing Brake Fluid

Your car's brake fluid transfers the hydraulic pressure throughout the brake system to stop the vehicle. Over time, this fluid absorbs water from the surrounding air and can become contaminated with dirt and debris. 

To ensure your brakes work as intended, most manufacturers recommend changing the brake fluid every 32,000 to 72,000 km or every two to three years. 

If you fail to change the brake fluid, the water it absorbs can cause oxidation inside the lines, which can cause damage to other brake components. 

The water also reduces the fluid's boiling point, potentially causing the fluid to boil due to the heat created by repeated stops. Boiling fluid can introduce air into the system and cause stopping issues. 

Risks of Not Changing Transfer Case Fluid

The transfer case is responsible for switching between a four-wheel-drive vehicle's various drive settings, such as two-wheel-drive, four-wheel-drive high, and four-wheel-drive low. Over time, the heat and stress the transfer case goes through can break down the oil and create sludge. Contamination can also get into the fluid and cause issues. 

Most manufacturers recommend changing the transfer case fluid every 48,000 km, though there may be a more frequent interval if you tow often. 

Failure to change the transfer case oil in a timely manner can result in shuttering and whining sounds from the transfer case in the short term. Over time, this can result in full transfer case failure. 

Risks of Not Changing Differential Fluid

Your differential is the last component that connects the drive wheels to the powertrain, so it endures thousands of miles of rotation and heat every year. Over time, the fluid that lubricates the differential can lose its viscosity and become contaminated. 

This is why most manufacturers recommend replacing the differential fluid every 48,000 to 96,000 km. If you fail to follow these recommendations, you may experience loud grinding or whining noises from the rear of the vehicle as the fluid breaks down. 

After a while, the stress may become too much for the internal components to handle, resulting in full differential failure. 

Check Your Owner’s Manual for the Correct Intervals

To know exactly when you need to change any fluids in your vehicle, you can go to the “Maintenance Schedule” in your vehicle’s owner’s manual. Here, you’ll find two sets of intervals for most maintenance items, “Normal” and “Severe.” Most Canadian drivers will fall under the “Severe” category because of our frigid winters. 

Always follow the owner’s manual’s maintenance schedule to ensure a long, healthy life for your vehicle. 

Fluid Type Matters too

While timely maintenance is critical, using the right fluids is equally important. Automakers design each system to use specific types of fluids and oils, and using the wrong fluid or oil can be just as bad as not changing the fluid or oil at all. 

You can find which fluid is right for your vehicle in the "Maintenance" or "Fluids" section of your car's owner's manual. If you don't have an owner's manual, you may be able to find a free PDF copy of it on the manufacturer’s website. If there’s not one available online, your local parts distributor can point you in the right direction. 

Start With a Clean Maintenance Slate at Clutch

With a Clutch pre-owned vehicle, you can rest assured you're getting a quality vehicle with all its maintenance done correctly and up to date. This assurance comes from our 210-point vehicle inspection and reconditioning process, which includes checking the maintenance schedule and performing any due maintenance. We also ensure all fluids are at their correct levels. 

On top of getting a well-maintained vehicle, you can also get the satisfaction of buying your new car without setting foot in a dealership. With Clutch, Canada's first online car dealership, you can complete your entire purchase online, even secure financing and value your trade-in

Once you choose the right car for you, we'll deliver it and give you a 10-day risk-free test own. If you don't love your vehicle, you can return it for a full refund or exchange it for something else within 10 days of delivery.