Should You Have Your Car's Transmission Flushed?

in Fluid

Depending on the make and model of your vehicle, and whether you purchase a rebuilt or new transmission, replacing the assembly can cost up to $3,500. For this reason, you should do everything possible to prolong its life. As with your engine, regular maintenance can go a long way toward protecting your transmission from premature failure. The good news is that maintenance is as easy as changing the fluid.

You may have noticed that the mechanics at your dealership or local repair shop recommend transmission flushes. But is the service necessary? More importantly, could it cause a problem with your car's tranny? In this article, we'll present both sides of the issue, so you'll be able to make an informed decision about the service. We'll also provide a quick "how to" guide for changing the automatic transmission fluid (ATF) in your vehicle.

Advantage Of Replacing The ATF

Some automakers claim that drivers do not need to change the fluid in their transmissions. They suggest the ATF can last the life of the assembly. Unfortunately, this claim may not be entirely true.

The fluid is filled with chemicals that help protect your transmission during operation. These chemicals ensure the gears shift smoothly and reliably. The problem is, the heat surrounding the assembly causes the temperature of the ATF to rise. This in turn causes oxidation; the chemicals begin to break down, and provide less protection to the tranny. When this happens, the moving parts begin to generate friction, which causes the shifting to become staggered or uneven. You'll notice a delayed response, or a jerking sensation when the gears shift.

Replacing the fluid introduces a new batch of protective chemicals into the assembly. They prevent the friction that can eventually destroy the gears and other components. Thus, changing the ATF prolongs its useful life, and postpones an overhaul.

So, how often should you change the fluid? A lot depends on the conditions in which you drive. Many mechanics suggest changing it every 30,000 miles, but placing a load on the assembly will accelerate the fluid's oxidation. If you normally drive aggressively, or haul heavy items up hills, you may need to change it every 20,000 miles.

Potential Hazards Of "Flushing" The Transmission

This brings us to the question of whether flushing your transmission is necessary and safe. During a flush, a special machine is used to push solvents at high pressure backward through the assembly. The solvents and pressure help to jar loose deposits and debris that have accumulated. By cleaning the system, the ATF can flow through it more easily, providing a higher level of lubrication.

There is a danger, however, that knocking loose the deposits will cause bigger problems down the road. For example, if the deposits are pushed through the assembly, but not expelled, they can create an obstruction that prevents fluid from flowing. This will essentially starve your transmission of ATF, which can quickly lead to costly repairs (or worse, an overhaul).

It is worth noting that flushes are generally not recommended for high-mileage vehicles (those with over 100,000 miles) for this reason.

Examining And Changing The Fluid

Thus far, we have explained why changing the ATF is a good idea, and the reason flushing your transmission is a poor one. We'll now explain how to do the former.

Before you start, check the scent, color, and consistency of the fluid. If the ATF is completely oxidized, it will smell as if something is burning. Next, place a few drops on a paper towel, and examine its color. If it is darkly colored, it needs to be changed. Observe its consistency as the drops spread on the paper towel. If the fluid is static (i.e. it does not spread), oxidation has already occurred.

Place sturdy jacks under the frame of your vehicle, and lift it. Locate the pan in which the fluid sits (typically, beneath the dipstick), and loosen the bolts that are holding it in place. Position a bowl or container under the pan to drain the ATF. Then, remove the pan. Some pans will be equipped with a drain plug that can be removed in order to drain the fluid.

With the pan removed and the ATF drained, clean any residual transmission fluid that remains in the pan. You'll likely see small metal particles; remove them, as well.

Next, replace the transmission filter, and the gasket around the perimeter of the pan. Install the new filter and gasket, and replace the pan before tightening the bolts. With everything in place, add the new ATF. Add it slowly, and check the level periodically to avoid overfilling.

The takeaway is that you should check your transmission fluid on a regular basis, and replace it when it becomes oxidized. But avoid having the assembly flushed since doing so can cause more harm than good.

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Lawrence Reaves has 1 articles online

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Should You Have Your Car's Transmission Flushed?

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This article was published on 2011/01/15