Transmission Flush vs Drain and Fill
 

I've recently been asked whether a transmission service should include a flush or drain and fill. Here's the advice that I've been giving on that subject.

If the transmission has been contaminated by coolant or other foreign material, then flushing will remove nearly all of the contamination. I recommend flushing by removing the oil cooler return line from the transmission and sticking that end in a bucket versus some mechanical power flush.

With the cost of today's fluids, a flush is going to consume a lot of fluid. All of the fluid that you push out of the transmission will go to recycle. After the intial load of fluid is pushed out, I recommend adding two quarts then repeat the process. Then add another two quarts, repeat the process a second time. You basically run the engine until you see air bubbles on the line that you placed in the bucket.

The other method involves draining the fluid from the transmission. This method typically removes half of the fluid. Then, put the plug back in and top off the transmission. This method uses about half the fluid of the other method.

A third possibility is to do multiple drain and fills. Let's assume that drain and refill changes about half of the fluid. The first time around you have 50% new fluid which is good enough for most applications. If you do it again, you end up with 75% new fluid and if you do it a third time, you get nearly all new fluid.

Good advise. I'd add that the process starts with the "paper towel" test where you pull the transimission dipstick and wipe on a white paper towel to inspect for color (reddish brown is good... black is bad) and for any debris. There is also a range of opinions on how often to do this. My view is if you do a single drain fill every 50K miles you pretty much get the same impact as doing multiple drain/fills every 100K - but the frequency is open for discussion.

I agree. I just did a service on a 2012 S60 with 50k miles. The fluid was more dark brown/black than red. So, we've done a drain and refill. I've recommended another at the next oil change.

10 quart flush on my 2004 XC70. Came out clean around 8.5 quarts in.

Wow - that Mobil 3309 fluid is about $7.25 per quart (at least that's what I'm paying). So, are you saying that you used 10 quarts to flush and then added enough to refill?

I used 10 quarts total. Drain the pan, add new fluid. Pump 2 quarts out from return, add 2 new quarts. Did this with 10 quarts total. I buy the fluid from the toyota dealership. Toyota type 4 atf is the same as the 3309 just a different name. Its about $5.25 a quart.

yep, Toyota and Volvo both use Aisin transmissions for the FWD models (some Volvo AWDs have Getrag or GMs if I recall). The key is to look at your owner's manual for the fluid required for your specific model/year. For example, my 850 spec'd 3309 but my 2000 S40 spec's Mercon III. Toyota TIV type 4 should be right for 3309. You can also find 3309 spec'd synthetics if you look around (may be worth considering if you live is a really cold climate as I've found full synthetics retain their viscosity better in the cold. I did a GL4 swap to Redline MT sythetic on my Quattro a few years back and was amazed how it improved the feel of the gears on a zero degree day's cold start

I didn't realize that an 850 ever used 3309 - I thought that were all either Dexron III or IV.