flush or not to flush

What does the owner's manual say? Generally, IMO, all this flushing of crankcase, transmission, etc. is mostly a means of getting into your pocket. Having said that, Consumer Reports magazine has reported that some engines suffer from sludge formation in the lubrication system and can benefit from periodic flushing.

You might try a Google on the subject to get more information or check with a Nissan technician. The so called Service Advisors in my experience have little technical knowlege and are mainly Service Sales people. I would not trust them to KNOW the answer. They are often paid a commission for sales made so YOUR best interests may not be their primary incentive when advising you.

Good to see your sceptecism.

I'd go with drain. While your car is not old, it's not young either, and the idea that a flush can possibly ruin your tranny just doesn't sit well with me. I'm sure the lube center make you sign an agreement saying that they are not repsonsible for any potential failure of the transmission after they flush the tranny fluid.

The drain and fill routine will, as you said, leave old fluid in the tranny. Despite that, that simple maintenance will add years of life to your tranny, especially since you're doing it before the tranny has developed any problems. Why not do 2 drains? That's what I do with my cars, both of which have over 100K miles. Once in the spring and once in the fall. My tranny will probably way outlast the rest of the car from this simple maintenance, and its inexpensive and diy.

Another thing to keep in mind: some trannies, like the BMW 7 series have a completed sealed unit. They don't ever need a fluid change.

I think you're right, the shops are just looking for another service they can charge you for. Maybe a NYC yellow cab may need a periodic flush because of its intense duty cycle, but most cars don't.

CD

My understanding is that a quality flush (e.g. BG) is preferable because it not only exchanges all the fluid but flows chemical agents through the system to thoroughly clean things. The build up of particles and sludge can eventually cause clogging of the tiny hydraulic passages in the valve body which will result in transmission failure. A quality flush machine will circulate fluid via the tubing that normally circulates transmission fluid through the radiator and do so in the same direction that the fluid normally flows. The determining factor as to whether to flush or not is the condition of the fluid. If it's looks clean and smells good, then flushing is good preventative maintenance every few years. However, if there is any doubt about the condition of the fluid, then leave it alone. If there is already some sludge buildup, then flushing may loosen sludge and who knows what it might clog up. In that case drain and fill is certainly safer and the preferable way to go. Good luck. Al