Which should you do?

The automatic transmission in your car or truck is one of the key drivetrain components.  It needs to stay working well.  Sadly, it’s often overlooked when it comes time to track the maintenance. Service intervals on an automatic transmission can be 8-10 times longer than your engine.  So, it’s easy to see why most people don’t remember to change the transmission fluid on time.

When it comes time to change the transmission fluid, there are a couple of considerations.  One consideration should be whether the manufacturer of your vehicle recommends just a fluid change or a complete system flush.  Your owner’s manual should list which is required.  Depending on the mileage of the vehicle, the type of service may be different.

What is an Automatic Transmission Fluid Change?

Transmission Fluid Change or Flush

A transmission fluid change is exactly as it sounds. You simply change the fluid in the transmission oil pan.  Depending on what vehicle you have, you may have a drain plug in the transmission oil pan that can be removed to drain out all of the transmission fluid sitting in the pan.

It’s common on older vehicles not to have a drain plug.  If there’s no drain plug, remove the fasteners holding the pan on to the transmission and allow the fluid to spill out.  Your vehicle manufacturer may suggest changing the transmission filter based on the mileage on the vehicle.  If you remove transmission oil pan, the filter is easily accessible once the fluid is drained.  Without removing the transmission oil pan, the filter can’t be removed and replaced.

The Transmission Oil Pan

The transmission oil pan fluid change will remove approximately 50% to 70% of the transmission fluid from the complete system. The transmission may have lines that run from the transmission to the front of the vehicle.  The lines cycle the fluid through the radiator or another cooler to keep the transmission cool while in traffic.  The body of the transmission may also contain a small amount of the fluid that doesn’t easily drain out.  To remove the remaining fluid requires a complete transmission system flush.

There are additional negatives of a transmission fluid change only removing most of the fluid from the system.  You may find that your vehicle has a plastic splashguard or a metal skid plate protecting the bottom of the transmission.  It will need to be removed to gain access to the drain plug or oil pan.  If you live in a snowy climate in the winter, you’ll likely find road salt, mud, rusty fasteners, etc.  Removing the pan can also be a little messy and requires a large reservoir to drain the transmission fluid.

Advice to Make a Transmission Fluid Change Easier:

  • If you plan to remove the transmission pan, start in one corner of the pan and remove only a few fasteners. Then slowly loosen the other fasteners around the perimeter of the transmission pan.  This allows your initial corner to slowly lower away from the transmission housing.  This helps the pan tilt, allowing the fluid to drain out of the initial corner into the oil pan reservoir.
  • Drain the fluid into a large catch reservoir.  The pan should be a 5-quart pan (minimum) with a wide opening for the fluid to drain into.
  • Wear personal protective equipment (PPE).  This includes safety glasses, gloves, and long sleeves.  If the vehicle has been run recently, the exhaust piping may still be hot.  The transmission fluid may also be hot.  A simple pair of disposable gloves may be easiest to wear during the fluid change process.
  • If you plan to change the transmission filter, have it ready install immediately after removing the old one.  This reduces the chance that contaminants enter the transmission while the oil pan is off.  Don’t forget to install a new transmission pan gasket.
  • Verify the required torque for the fasteners on the transmission pan before you finish changing the fluid.  Not tightening the fasteners correctly allows future leaks to occur.  Over-tightening causes the gasket to squeeze out leak fluid.  Use a calibrated torque wrench to tighten the fasteners per your owner’s manual or service manual.

What is an Automatic Transmission System Flush?

A complete transmission flush is different than a fluid change.  It replaces 100% of the old fluid with new fluid.  The benefit to a complete flush is that every hard-to-reach spot receives new fluid.  That keeps your transmission running cooler and receiving optimum protection.  New transmission fluid has the correct frictional properties for crisp shifts.  As the fluid deteriorates over time through use, friction and cooling properties also diminishes.

Eliminating Sludge

Sludge and other contaminants are accumulated over time and deposited in the transmission filter. Performing a complete system flush allows the use of a flush additive to help clean the transmission and more effectively remove accumulated sludge and other contaminants that may be hiding inside the transmission or system. One key note to using the flush is that you do want to change the filter also as the additive can collect inside the filter while the transmission is being cleaned. If you plan to only complete a flush without a filter change, the cleaning additive is not recommended.

The complete system flush generally costs more than a simple oil pan fluid change as you are removing and replacing 30% – 50% more fluid. You also will most likely be taking the vehicle to a professional that has a transmission flushing machine. The machine will connect to the transmission lines to remove and replace the transmission fluid in the system. The flushing machine also uses additional fluid beyond the capacity of the complete system to remove all contaminants, and that extra fluid contributes to the higher cost involved.

Is There a Better Option Than a Fluid Change or System Flush?

Both of the options mentioned have downsides, and if you plan to do the work yourself you may have a 3rd option that can do a better job than either would on their own. You can do a flush yourself, and change the transmission filter, which regenerates the transmission fluid system completely. With this method, there is a little math involved to explain why this may be the best option for you:

Let’s assume that with a fluid change you remove 70% of the transmission fluid by either removing the transmission oil pan or by removing the fluid through a drain plug in the pan. If you refill the transmission to full capacity, you have a mixture of 70% new fluid and 30% old fluid. You will then run the vehicle for a few minutes while shifting the transmission through the gears. You can do this by driving your vehicle around the block, or by putting your foot on the brake and sitting in the driveway shifting the gears.

The Purpose of a System Flush

The purpose it to ensure that the new mixture flows through every part of the transmission system. At that point you can again drain the transmission fluid out of the oil pan. You will then refill the system to maximum capacity with new transmission fluid. The 30% of the old fluid will be dropped to 9% old fluid in the system (30% x 70% = 21% new fluid), and you will replace 21% of the old fluid when you refill the system the 2nd time. You will again run the vehicle and allow the fluid mixture to flow through the complete system.

Once that is complete, drain the fluid out of the oil pan and this time you will change the transmission filter after removing the oil pan. Once you replace the filter, install the oil pan with a new gasket, you will refill the system back to maximum capacity with new fluid. This complete process replaces ~97% of the fluid in the system and a new filter is installed. It is a lot of work, especially if you don’t have a drain plug to remove the fluid out of the pan, but it does the best job of all three options.

What Transmission Fluid Does my Vehicle Need?

It used to be that you only could use a specific type of automatic transmission fluid in your automatic transmission, and the worst part was that each manufacturer required something different. Ford required a Type-F fluid, Nissan needed NS type, and General Motors wanted Dexron.

Buy Great Oil takes the worry and hassle out of what fluid you need by offering AMSOIL Synthetic Transmission Fluid that can work in any automatic transmission. It doesn’t matter if it’s a small car, an SUV, or a heavy-duty truck. Buy Great Oil can help you buy just the right automatic transmission fluid for your vehicle.

What if I Have a Continuously Variable Transmission (CVT)?

The CVT type transmission has been around in vehicles for many years, and servicing the CVT is similar to the automatic transmission. It will have a filter that can be replaced and will most likely have a drain plug to make changing the fluid easier. The CVT does not have the same friction clutches inside the transmission, so the service intervals will most likely be different than a traditional automatic. Finding replacement CVT fluid is easy, and AMSOIL has a Synthetic CVT fluid that will work in most available.

What if I Have a Manual Transmission?

The manual transmission is easier to maintain that an automatic or CVT. It doesn’t have a filter that needs to be changed, and usually doesn’t have a separate transmission cooler. However, it does require a different fluid than the other transmissions, but AMSOIL Manual Transmission fluid is also sold through BuyGreatOil.com.

It doesn’t matter what type of transmission you have in your vehicle. At some point it will need maintenance, which may include a complete fluid change, a system flush, a new filter, or just removing a drain plug to drain the oil from the transmission. The best way to know when the transmission fluid should be changed is to consult your owner’s manual, a proper service manual, or talk with a professional at Buy Great Oil. We also sell quality AMSOIL products for your vehicle and can offer a complete service package to keep your vehicle running smoothly for many miles ahead.

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