What Are the Different Fluids in Your Car? When Do You Change Them or Top Them Off?

February 17th, 2024 by

Oil is shown being poured from a container at a Ford service center.

A Ford has a lot of fluids coursing through it at any given time. Each plays a crucial role in keeping the vehicle operating at its peak. Over time, though, the fluids can get dirty or run low. This means either changing or topping off fluids yourself or bringing your vehicle to a Ford service center.

Failing to do routine automotive fluid maintenance will greatly increase your chances of having bigger, more expensive problems down the road. To stay on top of this, you need to know what fluids are in the vehicle, what they do, and why it’s essential to monitor these fluids regularly. While some fluids, such as engine oil, are widely known, some drivers might not realize there are also fluids for the transmission, the brakes, and even the steering system. Overlooking them can be dangerous to your vehicle’s long-term health.

At Jim Ellis Ford, we want every Ford owner to enjoy many years of great performance from their vehicle. This guide will introduce you to the different fluids in a vehicle and offer recommendations on how often to change them, check them, and top them off. The exact intervals of when to change automotive fluids depends on multiple factors, including the vehicle’s design and your driving habits. Consult your operator’s manual for the official maintenance schedule.

Engine Oil

This may be the most important fluid in your vehicle. As motor oil travels through the engine, it lubricates essential parts such as the valves, pistons, and timing chains so they work smoothly. Engine oil also cools these parts and removes dirt particles. Your oil cap typically lists what oil weight your vehicle uses (5W-20, 10W-30, etc.).

You have a choice of conventional, synthetic blend, and full synthetic motor oil. The general rule is to change conventional oil every 3,000 miles, blended synthetic oil every 4,000-5,000 miles, and every 5,000-10,000 miles for full synthetic oil. However, if your oil level is running low—which you can check using your dipstick—you should change your oil immediately to prevent damage.

Engine Coolant/Radiator Fluid

This is another fluid that helps keep the engine from overheating. It circulates through hoses to absorb engine heat and remove excess exhaust fumes. In turn, the radiator fins help remove heat from the fluid. Engine coolant is a mix of water and a chemical-based antifreeze, so it remains a liquid in cold winter temperatures.

The general recommendation is to change your engine coolant every three years or 50,000 miles, whichever comes first—though some newer vehicles can go up to 10 years/100,000 miles. When changing coolant, the old coolant must be completely flushed out of the system, or it will significantly reduce the lifespan of the new coolant. You should also check the coolant level regularly and top it off if it’s below the fill line.

A smiling mechanic is shown holing an oil container.

Transmission Fluid

Just as engine oil lubricates the engine, transmission fluid lubricates the transmission, keeping the gears, bearings, seals, and other parts from generating excess friction inside the gearbox. Automatic transmission fluid (ATF) is thinner and faster-flowing than manual transmission fluid (MTF). They also are different colors—ATF is dark red while MTF is brown or amber.

Some modern vehicles have transmission oil that can go up to 100,000 and even 150,000 miles between changes. On older vehicles, you should change the fluid when the vehicle gets to 60,000 miles, then at 30,000-mile intervals from there. If the fluid looks low or dirty, you should immediately get it changed, as failing to do so can lead to permanent damage. Debris in the fluid could also be a sign of an existing transmission problem.

Brake Fluid/Hydraulic Clutch Fluid

All hydraulic brake systems—which are found in nearly all vehicles on the road—use brake fluid to help the vehicle stop. Pressing on the brake pedal forces the fluid through the brake lines to your calipers, which then apply the force to the wheels. In cars with manual transmissions, the hydraulic clutch system is often pressurized using brake fluid as well. As such, old fluid or low levels can lead to a “soft” brake pedal, less stopping power, and shifting difficulties.

For most vehicle manufacturers, brake and clutch fluid should be changed every two years, completely flushing the old fluid before adding the new fluid. You should check the fluid every time you change your oil and top it off if the level looks low.

Power Steering Fluid

This works in much the same way as brake fluid but for your steering system. It hydraulically links the steering wheel and the front wheels, and it keeps other power steering parts, such as the pump and gearbox, lubricated. When fluid levels are low, turning is much harder, as your vehicle has basically reverted to an old-school manual steering system.

Steering fluid is generally only changed on an as-needed basis. The three main reasons for a change are if the fluid is contaminated, if you’re trying to correct another issue, or if part of the system has been repaired. As with brake fluid, you should check the power steering fluid at each oil change to see if it’s running low and look for signs of contamination.

Windshield wiper fluid is shown being poured.

Windshield Washer Fluid

When your windshield gets dirty, and there’s no rain in sight, this non-freezing fluid helps you clean it. In most vehicles, pulling on the windshield wiper knob releases washer fluid onto the windshield and simultaneously runs the wipers to clear away grime and streaks for better visibility. Some cars also let you use washer fluid on the headlights.

You don’t ever need to change washer fluid, but you will need to top it off regularly—you don’t want to be stuck with a filthy windshield and an empty fluid reservoir. Again, checking the washer fluid level when you’re getting your oil changed is a good rule of thumb.

Rear Differential Fluid

Also known as gear oil, this is especially important for vehicles with four-wheel drive or all-wheel drive. The differential/transaxle accounts for the difference in turning radius between the outer and inner wheel, adjusting power to each for smooth handling. Differential fluid keeps the internal parts cool and well-lubricated. It looks and feels like a thicker version of engine oil. What gear oil you’ll use depends on whether the vehicle has an open differential or a limited-slip differential.

The fluid changing and top-off rules for the rear differential are the same as the transmission, which can be anywhere from 30,000 to 150,000 miles. Low fluid will cause grinding and excess friction in the differential gearing. Since there’s no filter, you can end up with metal shavings in the fluid that can cause further damage.

Vehicle Service at Jim Ellis Ford

Staying up to date on Ford fluid maintenance will ensure your car, truck, or SUV performs its best. A quick check-up or maintenance appointment can save you time, money, and heartache later.

Whether you know you’re due for an oil change or are unsure of the transmission fluid status, you can schedule all your Ford vehicle maintenance at Jim Ellis Ford. Our service center is staffed by factory-trained Ford technicians, and we always have the right fluids and tools needed for your vehicle model. Our certified oil changes include fluid top-offs, so you know your fluid levels are where they should be. We also offer vehicle pickup and delivery plus a loaner fleet to get you where you need to be.