What Fluids in a Car Need to be Changed?

When your engine is in operation, a lot of metal parts rub against each other. This rubbing would generate a lot of friction and heat without oil to lubricate the engine’s internals. Engine oil also acts as a coolant to keep hot engine parts, like the bottom of the piston and skirts cool.

Traditional wisdom puts the oil change interval every 3 months or 3,000 miles, but this interval will differ depending on your year, make, model, and engine, as well as the type of oil you use (conventional or synthetic). Check your owner’s manual for the correct interval.

Regardless of whether you have a manual or Automatic transmission, it contains fluid that needs to be changed in intervals. This fluid lubricates the gears and synchros in a manual transmission, and does the same with clutch packs and gears in an automatic transmission. You don’t need to change transmission fluid nearly as often as oil, but it’s important to note that neglecting it can quickly lead to transmission failure, which is nearly as costly a repair as changing an engine. Most manufacturers recommend transmission fluid changes between 25-40,000 miles.

Most braking systems use hydraulic fluid with a Master Cylinder to compress Brake Calipers, which then squeeze the pads to the rotors and bring the vehicle to the stop. Brake fluid is hygroscopic, which means it absorbs water, which leads to rust, corrosion, and a lower boiling point for brake fluid, which operates at extremely hot temperatures near the caliper. Brake fluid should generally should be flushed every 25,000 miles or when the pads and rotors are replaced. Learn more about flushing brake fluid here.

Engine coolant, or antifreeze, does what it sounds like it would do: it cools your engine. Without it, the engine would overheat and seize. When you need new coolant and what coolant you need depends on what you drive, so check that owner’s manual, or read here about what antifreeze you need, or how to flush and fill it.

Hydraulic power steering systems use hydraulic fluid similarly to how brake fluid works. Over time, this fluid goes through a multitude of heat cycles, gets dirty, and begins to break down. Power steering fluid generally gets neglected the most out of any fluid, but it also tends to last the longest. A service interval of 60-80,000 miles is generally ok.

No matter what kind of car you have, you have some form of a differential, which through a series of gears, transmits the engine-to-transmission torque to the axles and wheels. 4 wheel drive vehicles generally have a front and rear differential, and many AWD vehicles have a center differential as well as a rear. This gear oil breaks down over time, gets dirty, and needs to be changed. Most manufacturers put the interval at 80-120,000 miles, so check accordingly.

Washer fluid isn’t a crucial maintenance fluid in that your car can still function without it. That said, you’ll regret not topping it up if something gets on your windshield while you’re driving. There are special formulations for removing bugs or ice and frost as well as general purpose fluids. There’s no precise interval for replacing this fluid, but you can check it under the hood and fill up as needed.

It’s important to note though, that different washer fluid has different freeze temperatures, and if you live in the northern half of the country that encounters below-15 degree temperatures, it’s important to note that not all washer fluid is equal. Summertime washer fluid, like Bug Wash, can freeze in sub-zero temperatures, rendering your washer system useless when you most need it. Once fall comes, it’s a great idea to get any summertime fluid out, and replace it with De-icer, which is always rated into negative temperatures.