Why Flushing Old Fluids is More Important to Your Car Than You Think

Have you ever had a mechanic tell you that your car needed some type of fluid flushed out and replaced?

You may have thought “What a scam”, only to find out later that it wasn’t a scam?

Maybe you did the recommended flush, but you wondered if it was really necessary.

In today’s article, we are going to talk about all the fluids in your car, why and when they need to be flushed, and everything else you need to know about this important maintenance item.

Is It Fluid Flush or Fluid Change? What the Heck is the Difference? 

This is probably where most people get confused. One person may tell you that all you need to do is change the fluid, while someone else says you need a flush. What’s the difference and how do you know which is correct?

First, changing the fluid simply means draining and replacing. An engine oil change is one example. You simply drain out the old oil and replace it with fresh oil, correct?

A flush, however, is a much bigger job.

Flushing a fluid means that after the mechanic drains out as much of the old fluid as possible (let’s say brake fluid for this example), the mechanic uses a device that flushes or washes out every bit of the old brake fluid, so the system is completely clean. New brake fluid can then be added.

What Fluids Need to Be Flushed? 

Not all fluids in your vehicle need to be flushed and some only rarely.

For example, your car’s engine is rarely flushed. If it was contaminated in some way (let’s say your neighbor’s kid poured a can of rubber cement into the motor) then it will need to be flushed, but this is not common because it isn’t really needed.

The three major components that require regular flushes are as follows: 

1. Coolant

While the cooling system in your car is sealed, coolant does wear out over time. Most people simply top off their coolant with a bit of water should it become low.

However, keep in mind that coolant comes in many colors and those colors really matter. Depending on the year of your vehicle, you will need a different colored coolant and NO, you cannot mix them!

If you see any sludge, if your coolant takes on a dirty brown color, or if it’s been more than 30,000 miles, you should definitely have the entire system flushed.

Flushing a coolant system not only removes old coolant, but it removes rust and scale that has built up over time.

Most radiator or coolant flushes cost less than $130 and it’s well worth the expense.

2. Automatic Transmission Fluid

Many people are under the impression that automatic transmission fluid lasts forever. This is 100 percent false.

Your automatic transmission fluid, or ATF, should be a red, nearly transparent color. When your ATF becomes really dirty, it turns a dark brown or very dark no longer clear red color.

When ATF wears out and becomes very dirty, it can no longer protect and lubricate the internal transmission parts. This allows varnish and sludge to form inside the transmission.

While most transmissions have filters that can be changed and some fluid that can be drained, the majority of the dirty transmission oil is inside a large tank called the torque converter, which holds about 3-5 quarts of transmission fluid. The torque converter has no drain plug and the only way to remove all of the dirty trans fluid is to flush the system.

A complete flush may cost as much as $300, but this is well worth the price when you consider what a transmission overhaul costs. Flushing the system will remove all of the old, dirty transmission oil and remove all the sludge and metal particles that can damage the transmission.

The best news about a transmission flush is that you probably only need to do this every 50-60,000 miles. Check your owner’s manual for the recommended mileage for your year and model.

3. Brake Fluid

No one would argue that the brakes on your car are extremely important, so you want to keep them in the best possible working order.

Most people are unaware that brake fluid is hygroscopic, which means that it absorbs moisture from the air, even if the container appears to be tightly sealed.

Water inside your braking system causes brake parts to rust from the inside out, which is something you can’t see. Unfortunately, rust will not stop until the part is completely eaten away.

One indication that your brake fluid may have accumulated too much water is brake fade. If you have to push harder and harder on the pedal to get the car to stop, but the brake pads are fine, you may need to have the fluid flushed.

You can inspect the brake fluid reservoir on the top of the brake master cylinder. The fluid should be a slight yellow color but completely clear. If you see little black floaters, these are rubber pieces that are deteriorating inside the system. You might also see a reddish/brown goo on the underside of the cap. These are all signs that the brake fluid has been contaminated and needs to be flushed.

Most brake fluid flushes cost about $125, and they should be done about every other year.

Other Fluids

Most other fluids do not need to be flushed unless they become contaminated. Some other systems in your vehicle that may require a flush include:

• The power steering system. While this system doesn’t often need flushing, in older cars, the pressure hose can deteriorate over time and fill the system with tiny rubber particles. If this happens, you will need to flush the system.

• Motor oil. As we mentioned earlier, the engine doesn’t usually require flushing unless it was somehow contaminated. Sometimes, if the head gaskets leak, it can allow oil to enter the cooling system or coolant to enter the motor. Your mechanic may want to flush the motor in this instance to ensure that both systems are clean and ready to be repaired.

• The windshield washer. Flushing this system doesn’t take much more than some compressed air and it rarely needs to be flushed, but if a family of bugs somehow made the windshield washer bottle their home or if a hole in the system filled it with dirt or other items, flushing this system is quick and easy.

The Bottom Line

You might hear some people say that you can do fluid flushes at home, but we don’t recommend that.

You need the proper equipment, the proper cleaning products (Dawn dish soap isn’t going to cut it) and you need to use the correct replacement fluids for your year and model.

At Hong Kong Auto Service, when we flush any system in your vehicle, we also inspect it for leaks, any possible damage, and we can make repairs right on the spot before your vehicle breaks down and leaves you stranded.

Take your car, truck, or SUV to the professionals at Hong Kong Auto Service. Call us today for an appointment and your car will be ready for wherever the road takes you.