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Complete Guide: When to Change Your Vehicle’s Fluids

Guide to when to change your car fluidsThe fluids in your vehicle are to ensure it runs smoothly, prevent overheating of components, and in some cases, create hydraulic pressure to operate. Though fluids can last for many miles, over time they begin to break down and lose their ability to perform as well as they once did. 

Flushing these fluids at the recommended intervals help your vehicle function optimally and extends its life. With so many different fluids in your vehicle, it can be difficult to know what each fluid does and more importantly, when they will need to be changed. 

It’s been instilled in you since you started driving that the most important fluid to change is the engine oil. It’s considered the most vital fluid because it keeps internal engine components cool and lubricates moving parts to prevent metal to metal contact.

 It’s true that oil changes should be performed every 3,000 – 5,000 miles and that engine oil is important, but there are other fluids that greatly contribute to the function of your vehicle that are also important for operation. Read on to learn how each fluid helps your vehicle and when they should be replaced to keep your vehicle running as good as new.

Brake Fluid

Brake fluid is a key element in getting your vehicle to slow down or stop. The brake system is a hydraulic system that is highly pressurized. That pressure is made to increase considerably, enough to stop your car. When the brake pedal is pressed down, the brake fluid enters the pistons in the brake calipers and cylinder at each wheel. The pressure is increased sending the fluid into motion, signaling to the brake pads to press down onto the rotors attached to the wheel to stop rotation. When a vehicle is out of brake fluid, the system is unable to create pressure which is extremely dangerous as it may prevent the vehicle from stopping all together. 

When to change brake fluid: Every 30,000 miles

Power Steering Fluid

Power steering fluid is the fluid that makes turning the steering wheel much easier. The fluid is pressurized by a hydraulic pump driven by the engine and is meant to keep the internal steering mechanisms lubricated and prevent failure. Because of the heat generated from the creation of this pressure and fragments of seals, hoses, and gaskets collected within the fluid over time, the fluid begins to weaken and needs to be replaced.

When to change power steering fluid:  Every 30,000 miles

Transmission Fluid

Transmission fluid is an important fluid for several reasons. In addition to lubricating moving parts, it helps to keep the transmission cool from the heat created from friction and keeps gaskets and other components conditioned for maximum efficiency. Many vehicles today are equipped with sealed transmissions. However, sealed does not mean inaccessible. The fluid in these systems still require inspection and replenishment but are only accessible by a technician using specialized equipment to access the unit. 

When to change transmission fluid: Every 45,000 miles or every 3 years


Also known as coolant, antifreeze is a heat transfer fluid that is used to keep the engine cool and lubricated as well as prevent freezing in colder temperatures. Coolant is made to travel in and around the engine and collect heat where it returns to the radiator where heat is dissolved into the air and continues as the vehicle runs. After a great deal of use and time, coolant accumulates contaminants such as dirt and rust particulates that lessen the effectiveness of the fluid and maintaining a stable temperature of the engine. 

When to change coolant: Every 30,000 – 50,000 miles

Differential Fluid

The differential on a vehicle receives and distributes the power, generated by the transmission, to each wheel and adjusts the difference in speed and direction in each wheel. Wheels often turn at different speeds and varying distances. For instance, when the vehicle turns, the inside wheels have less distance to travel than the outside wheels. Each vehicle’s differential makeup is different. In a front wheel vehicle the differential is called the transaxle as it shares the same gear oil and housing as the transmission. Some vehicles can have as many as three differentials for both the front and rear as well as a transfer case. The differential fluid is one of the most overlooked fluids when it comes to maintenance, however, it is equally as important as engine oil because it prevents the premature wear of components from overheating and metal on metal contact.

When to change differential fluid: Every 30,000 – 50,000 miles

Diesel Exhaust Fluid (DEF)

DEF is an element required for selective catalytic reduction and is used to reduce the emissions emitted into the air from medium to large diesel vehicles. Diesel exhaust fluid is a combination of urea and deionized water that is used to convert dangerous nitrous oxide into water vapor. When added into the exhaust stream, water is made to evaporate and the remaining molecules of ammonia travel to the catalytic converter where it is transformed into water vapor for cleaner emissions.

When to change Diesel Exhaust Fluid (DEF): There is no specific mileage when this fluid should be added to the reservoir as consumption per vehicle varies. A good rule of thumb is to add the liquid every third or fourth time you refuel. 

Sun Auto Service Major Service Special

With all the different fluids in your car, it can be difficult to keep track of all the service intervals of when each fluid should be changed. At Sun Auto Service we’ve simplified the process for you. With our Major Service Special, performed every 30,000 miles, you can rest assured your vehicle’s fluids are in the best condition for its operation. The Sun Auto Service Major Service Special can save you money over having each service done individually. The Major Service Special includes these flushes:

  • Brake Fluid Flush
  • Power Steering Flush
  • Cooling System Flush
  • Transmission Flush

In addition to all the vital fluid flushes, the Major Service Special also includes:

  • Lube, Oil, & Filter
  • Tire Rotation
  • Battery & Charging System Check
  • Scan of On-Board Computer for Codes
  • Clean and Adjust Rear Brakes
  • Inspection of Throttle Body & Injection System
  • Air Filter
  • Multi-point Vehicle Inspection 

When it’s time to replenish the fluids in your vehicle, look no further than Sun Auto Service. We know how to care for your vehicle whether it’s a luxury machine, the family minivan, or a commuter car. Vehicle repairs and maintenance on every make and model is our specialty. Visit a Sun Auto Service for your vehicle’s maintenance or to create a maintenance schedule for your vehicle, today.