If you do a lot of driving under high-stress conditions, you should check the transmission level more often and have a repair shop check the condition of the fluid. Transmission fluid often is red but can come in other colors, and as it deteriorates it tends to turn darker. It may also acquire a burned odor that could indicate it needs to be changed or that the transmission is developing mechanical problems. Another indication it needs changing is dirt or other debris in the fluid. When you take your vehicle in for an oil change or other routine service, the repair facility may urge you to pay for a transmission-fluid change or flush. Even if they can show you that the fluid is darker than original, that might not mean you need fresh fluid right now. Step back, check the maintenance schedule in your owner’s manual and see what the manufacturer recommends before you decide. This also will give you time to price shop.
Before draining or flushing you should pull the dip stick and look at the fluid. If it is dark, burnt smelling, and you see little flakes or speck in it, do not flush The fluid and transmission possibly has hard part damage, but the transmission just has not figured out it should die yet. If you flush a transmission in this condition it could fail right away. Real strange, but that is what seems to happen. If your transmission is in this condition just drive it while you save for a replacement transmission. There is no way of telling when it will fail. It might be today, next week, or next year, but it is doomed.
The goal here is to flush the transmission before the fluid gets contaminated. What you are taking out should look like what you are putting in. Do not wait for a color or smell change. Most manufacturers calls for transmission fluid change at 30,000 mile intervals. The industry standard is two years or 24,000 miles whichever comes first.
a transmission flush and a fluid change are two completely different services. While a transmission fluid change focuses on draining the dirty fluid from the pan, a transmission flush gets rids of all the fluid in the pan, the cooler lines, as well as the torque converter. While it depends how often you should have your transmission serviced, it also matters which service you choose.
Whichever service you choose, make sure that the transmission filter is replaced, the fluid recommended by the manufacturer is used, the pan is dropped and inspected for any problems.