When it comes to keeping your automatic transmission in great shape, preventative maintenance is an absolute must. It doesn't take long for transmission fluid to break down under the intense heat and stress, which is why having it replaced every 30,000 to 60,000 miles is so important.

So when it comes time to change your transmission fluid, should you click here for info about the process and have it done by way of a transmission flush or should you opt for the more traditional "drain and fill" procedure? The following explains the benefits and drawbacks of a transmission flush and whether or not you should have it done for your vehicle.

Flushing vs. Drain and Fill

During a fluid change, your mechanic will drain the transmission fluid via the pan and replace the transmission filter. However, this "drain-and-fill" method only removes a portion of the old transmission fluid. Up to half of the transmission fluid could be trapped in hard-to-drain places, such as the torque converter and transmission cooler lines.

It's not uncommon to see a mechanic drain and refill a transmission multiple times just to dilute the old fluid to acceptable levels with new. Transmission flushes, on the other hand, remove all of the old fluid in one fell swoop. During a transmission flush, a specialized machine helps push the old fluid out of the transmission while feeding new fluid inside. Some machines feature a pump that actively flushes the transmission fluid, while others use the vehicle's own power to flush out old fluid.

With a transmission flush, it becomes much easier to flush out old fluid that's trapped within the torque converter and other various crevices. A flush can be done in under an hour, in most cases, making it a quick way of changing your transmission fluid. On the other hand, a transmission flush usually costs more to perform than a simple drain and fill. According to Angie's List, the average flush costs $100, whereas the price tag for a drain and fill may be limited to the cost of the fluid and transmission filter, especially if you decide to change the fluid yourself.

When to Flush

Here's the best time to flush your transmission fluid:

• When your vehicle approaches its recommended transmission service interval (30,000 to 60,000 miles)
• If the old transmission fluid still looks relatively healthy (reddish color, minimal odor and no signs of metal flakes)

Before you take your vehicle in for a flush, it's a good idea to take a look at your transmission's dipstick. As explained below, you don't want to flush your fluid if it looks to be in bad shape.

When Not to Flush

The whole point of a transmission flush is to clean the fluid before it breaks down or becomes contaminated. So if your transmission fluid has a nearly-blackish appearance, smells burnt and has little flakes of metal in it, then the opportunity for a transmission flush has already sailed by. In fact, you don't want to change your transmission fluid at all.

As strange as it might sound, changing your transmission fluid after it's gone past the point of no return will likely cause it to fail in short order. This is because the old transmission fluid has the clutch material that's worn off as the fluid deteriorated. Flushing the transmission in this state removes that clutch material, which may cause the transmission to start slipping or even fail outright.

Another reason to avoid flushing your transmission is if the manufacturer specifically prohibits it. Your manufacturer may have another way of changing your transmission fluid and, in some cases, may even avoid your warranty if it's done improperly.