So I have a 2002 Olds Alero with 166,000 miles on it. I bought the vehicle from a federal auction in 2004 when it had 49,000 miles on it. Although I have regularly had the engine oil changed every 3-5K miles (Moblie1 full synthetic), I don't actually know much about cars so I never had the transmission fluid drained until recently at 164,500 miles. There is no easy to check dip stick for the transmission, its apparently a sealed unit with a spot for checking fluid on the underside.
The shop wanted to do a full transmission fluid flush, but after I asked a question on this site regarding transmission flushes I opted to have them drop the pan, drain and fill. They said they put in about 7 quarts of transmission fluid. They actually recommended a transmission flush after another 6,000 miles (of course I'm thinking I could have just done that in the first place). I voiced my concerns about stirring up debris that would settle into the wrong places.
However I realize the first drop, drain and fill did not remove all the old transmission fluid. So I'm thinking I probably should have something done in another 6000 miles or so. The shop is saying that if I don't do the flush it will still be mixing old fluid with new. My question is, should I have another transmission fluid service in 6,000 miles and if so, is another drop, drain and fill the way to go vs a flush?
I'm sure I've been lucky to have not had any transmission problems so far, that may be due to the fact the I drive it very, very gently. I never speed off the mark from a stop and rarely ever drive over 70 mph. Almost all the miles on the car are freeway miles.
How you drive doesn't have that much to do with how long the transmission will last. I have 241,000 miles on my '88 Grand Caravan and I regularly drag around a tandem axle enclosed trailer that's bigger than that van, and the fluid and filter has been changed once in the life of the van, only because the $3.50 side cover rusted out so I had it apart anyway.
The fluid and filter change was always the standard procedure at every 36,000 miles or three years. There never was such a thing as a transmission flush machine until we started running into trouble with computer-controlled transmissions in the '90s. A lot of that was due to the parts being made lighter and cheaper for better fuel mileage and to save money. Flushes don't fix cheap.
We have all heard the stories about transmissions failing shortly after they were flushed. The thought is debris is washed out and circulates around, then chews up the seals it gets caught in. There's a lot of arguments against that. First of all, flush machines push fluid around the same places the transmission's pump does so if anything was going to be dislodged, that would have happened a long time ago. Next, that debris would get stuck in the filter. One guy I worked with who was teaching transmissions even went so far as to believe the "grit" that makes up the fiber clutch plates had broken off the plates and was circulating with the fluid, and it was needed to keep the clutches from slipping. If you drained it out you would have slipping problems after that. He didn't have an answer as to why that grit didn't chew up the seals, and why, if that material had flaked off the plates how they could grab at all.
My thought is not many people get their transmissions flushed for general maintenance. They show up all of a sudden after they notice some problem developing, then think the flush is going to cure everything. In reality, by the time there are symptoms the damage or wear has taken place and new fluid isn't going to help.
My suggestion is if you aren't having a problem, have the fluid and filter replaced again in another 36,000 miles, or whatever is recommended in the owner's manual. Engine oil is changed much more often because the additives wear out and there are combustion byproducts that settle in it and form sludge. We don't have that trouble with transmission fluid.
If you do develop a transmission problem it is not going to be due to not having it flushed. It is going to be due to high mileage and normal wear.