In the previous post about automatic transmission service intervals, we presented that heat is the enemy of transmission fluid. Heat causes the fluid to deteriorate, reduces its ability to lubricate, increases friction on internal parts, and leads to shortened transmission life.
Choosing the best transmission service type or procedure can be a challenge because recommendations vary depending on whom you ask or where you research. Start with your vehicle’s manufacturer service schedule in the owner manual. It suggests your best “minimum standard” for service mileage recommendations. It also indicates if the fluid and filter should be changed or just the fluid.
Understanding the difference between the three fluid service types
There are three basic automatic transmission services:
- Machine flush service
- Drain and fill with filter replacement
- Drain and fill
During machine flush transmission service, the transmission cooler hoses are connected to the flushing machine. Clean fluid is forced into the transmission and torque converter essentially forcing out the old fluid. Some repair shops tout a flush as “the best method” because a drain and fill service doesn’t remove all the old fluid from the torque converter, which can retain between four to eight of the 12 quarts of fluid in the system. When the drained fluid is replaced and the engine started, the old fluid held in the converter circulates and mixes with the new fluid.
The logic behind flushing sounds good, but be aware that some transmission technicians do not recommend the procedure, and certain manufacturers like Honda have published bulletins against machine flushing procedures. Here are some problems flushing can create:
- Metal and particles that would normally lay in the transmission pan or other locations can be stirred up during a flush and circulated throughout the transmission causing additional wear or even failure
- Very small orifices found in some solenoids can become blocked by debris and fail to function
- Restricted transmission filters are not cleaned by flushing
Drain and fill service with filter replacement
A transmission drain and fill with a filter replacement had been the main method of transmission service since automatic transmissions were first installed in cars. Today, it’s still the most common service method used and involves removing the transmission pan, allowing fluid to drain out, replacing the filter, replacing pan gasket with a new one to avoid leakage, reinstalling the pan, and then replace drained fluid with new. Most often, this service won’t remove fluid from the torque converter, which will then mix with the new fluid on start-up.
Drain and fill service without filter replacement
Many newer vehicle transmissions don’t have a replaceable transmission filter and are equipped with a drain plug to remove and allow old fluid to drain out. Some manufacturers recommend the vehicle be driven after the initial drain/fill process to purge old fluid retained by the torque converter. Then the drain and fill is repeated providing a better exchange of old fluid volume for new.
What to consider when giving approval for a transmission flush
Flush services are a profit center for many repair shops and are frequently the procedure that is recommended for vehicles with or without transmission filters. Since it takes a technician a few minutes to hook up the machine, he can then work on another job while the flush is running. This service requires less time and can be less costly to the customer than services with transmission filter replacement.
Keep in mind:
- Check your owner manual and online OEM resources to determine if flushing is right for your vehicle. Flushing a transmission in the presence of extremely dirty fluid may result in transmission failure as an undetected problem may be the cause of excessive fluid contamination
- If your vehicle is still under manufacturer warranty, request that the repair professional make certain machine flushing doesn’t void your warranty
- Transmission service seldom fixes an existing transmission problem. If you are having shift problems the best thing to do is schedule an appointment to have the problem diagnosed before it gets worse or causes more damage
At AutoTranz Transmissions, we believe the best way to avoid costly repairs is by having your transmission serviced at the recommended intervals. We do filter replacements when they apply and otherwise offer economical and reliable drain and fill services, the safest way to make sure your hard working transmission continues to function efficiently and reliably.
Visit us online to request an appointment or call (208) 722-7429 to schedule your next service or repair.