Why You Can’t Remove All of Your Old Automatic Transmission Fluid

If you have been religiously changing the oil in your automatic transmission in accordance with manufacturer recommendations, your intent may have been laudable. But if you are simply draining the oil and topping up at the other end, you may not be doing a complete job. Why is this, and what should you be doing instead?

The Need for New Oil

As time goes by, new transmission oil will begin to degrade. Microscopic particles of metal will wear away from some of the internal components due to the natural forces of friction and elevated temperatures. Many of these particles will be caught within the filter system, but some will remain in suspension and will affect the oil's ability to perform.

The lubricant will thicken as it gets older, and this will also affect its capability. If it were to be left unchanged, you could expect to see some damage as the risk of friction and metal-to-metal contact would be much greater.

Trapped within the Doughnut

Clearly, changing the old fluid and replacing it with new will make a difference. However, due to the design of an automatic transmission system, some of that lubricant will remain in place even when you remove the extraction port. Much of it will be trapped within the torque converter, a doughnut-shaped component that sits in between the engine flywheel and the gearbox. Within the converter is an impeller that spins rapidly, and flings pressurised lubricant against the inner side of the container. This lubricant will not be able to flow out when you remove the drain plug, and you will need a special device to capture it.

Extraction System

If you take your vehicle to your local mechanic, they will use an oil extractor pump that will be connected to the drain pump to perform a full flush. Some machines also pump cleaning fluid through at the other end of the gearbox, which makes sure that the internal workings of the torque converter are as clean as possible.

Worth the Effort

These days it pays to do as much as possible to look after your vehicle so that it retains its value and lasts as long as possible. So the next time you are ready to replace your automatic transmission fluid, outsource the job to your local service station. They will ensure that the vehicle is fully flushed and gets top-quality replacement lubricant.

For more information on automatic transmissions, contact a professional near you.