The fluids in your vehicle are the blood of your car. Over time, fluids need to be changed. There are a number of factors that cause your engines fluids to degrade.
When oil goes through heat cycles, it gradually become less viscous and more acidic. Some of the fluids in your car experience worse heat cycles than others. Engine oil and transmission fluids experience extreme heat.
As pumps, engines and clutches in your engine experience normal wear, small pieces of metal, dirt and clutch material are suspended in the oil. Engines and transmission experience this a lot so they also have filters to clean out some of the debris to keep it from doing damage. Power steering systems, for example, don’t have as much suspended debris in the oil so they only rely on fluid changes to get rid of it.
Over time, your fluids absorbs foreign fluids that can corrode your vehicle’s systems. The classic example is your brake fluid. Brake fluid is engineered to absorb water to keep it from rusting out your brake’s hydraulic systems. But brake fluid can only absorb so much water before things start getting damaged. When water is absorbed into brake fluid, it cause the fluid to boil at a lower temperature. Brake’s generate a lot of heat. If your fluid get’s too old, absorbing too much water over time, your brakes heat could exceed the boiling point of the fluid which would cause you to lose your brakes.
Your coolant (or antifreeze) is designed to lubricate your “water pump”, which circulates the coolant through your engine to keep it cool. Coolant resists freezing at extremely low temperatures and also coats the inside of your engine to keep it from corroding. Old coolant gradually loses it’s ability to lubricate your engine’s water pump and can actually corrode the inside of your engine.
When should your fluids get changed?
It all depends on the type of fluid used in your car. For example, synthetic oils maintain their viscosity (slipperiness) much longer, than less expensive regular grade oil. Some vehicles come equipped with other extended life fluids designed to lower the maintenance costs of your vehicle.
The following is a general rule of thumb:
Engine Oil – every 3 months or 3k miles
Transmission fluid – 30k miles
Engine Coolant – 30k miles
Brake Fluid – 30k miles
Power Steering Fluid – 30k miles