2004 XC90 2.5T Transmission Drain/Refill vs Flush

[Volvo Family]

Just had a multi-point inspection performed by Volvo. The technician said there was some sediment in the transmission fluid and recommends a transmission flush. I have scoured this Forum as well as some others and found that there is a difference of opinion when it comes to "flushing" a transmission on a vehicle with high mileage.

Is it safer to empty the fluid from the transmission drain plug and then replace with equal parts of new fluid?

If "flushing" the transmission is optimal, which method is safer for my vehicle; Manual flush or Machine operated flush? I have read conflicting reports on this and I am concerned about creating a fatal transmission problem.

Some facts to facilate your answers
My vehicle has 93,500 miles
According to the forum this is an Aisin Warner 5 speed automatic.
I just purchased this SUV. There is no evidence of a previous transmission fluid change. Carfax is clean. Volvo NA reports that previous owner had all recalls performed; no outstanding recalls/warranty issues
The fluid of overwhelming choice will be Mobile 3309 ATF
No evident transmission problems when driving.

[jimmy57]

OK, here is the WHOLE story: That gear box has no "real" filter. It has a strainer to prevent the pump for taking in particles too big for it handle without damage.
The pickup for the oil is made onto the filter and is doesn't go to the very bottom of transmission and is forward in transmission.
Part of the filtration is nothing more than letting stuff settle and sit in bottom of transmission.
Drain and refill will let some, maybe most, of the sediment out.
Drain and refill does not get the sediment out of the torque converter if there is any.
Flushing using a branded machine will involve introducing a chemical detergent and the machine will be put in the flow path to the fluid cooler and they will run the car and let the fluid go through the machine and it either catches it in a filter in machine or some machines have a centrifuge.
After a time they switch the machine over to drain and it takes dirty fluid into a storage tank while metering in clean fluid through the other line until the capacity of trans has been exchanged.
Flushing will get you clean fluid again by filling in numbers on your check.
They may use a universal fluid with an aftermarket company provided dose of magic elixir that makes the uni fluid into the manufacturer spec fluid (???). Often they will offer the use of manufacturer fluid but upcharge for that fluid.
Third choice is home flushing with no detergent and no machine.

My personal choice is drain and refill. If the fluid is really bad then get it hot, run it in and let it drain all night. Probably two extra quarts will come out as the torque converter will drain a bit in those hours.
I would do the overnight thing a couple of times close together to get it clean.
The REALLY clean solution is a combo. Two overnighters to get the sediment out and an exchange flush to get as complete of a new fluid load as possible without dismantling transmission and cleaning ALL the parts.
I've inspected a trans dismantled after a chemical machine flush didn't fix the issue and I was underwhelmed with the sediment on bottom of trans but the fluid looked clean.

The issue where a flush makes a previously working transmission no longer work is not something I have seen on these 5 speeds.

The lowest risk is the simple drain and fill. Changes the fluid more gradually.
Next is overnight drain and refill.
Next is o'night plus home flush to exchange it all

[MoVolvos]

-
Here is a recent discussion on Transmission fluids.

https://www.matthewsvolvosite.com/forums ... =1&t=47877

Blessings,
BKM
-