How long to drive between multiple drain/fill to get fluid mixed?

[vinu_neuro]

The ZF 8-speed in our Q5 holds around 9L total and 4.5L can be drained out at once. I plan on doing three drain/fills to get to around 85-90% new fluid.

How many miles do you generally need to drive to get the new and old fluid mixed?

I want to drive it sufficiently enough to not be draining out the new fluid. Normally I would give it a week between changes, but I'm constrained by time as I am borrowing a friend's lift (2hr hours away) to do this trans fluid/filter change.

 

[JavierH19]

A mile is fine. But 3 drain and fills is unnecessary. Two is enough because of diminishing returns on the fluid exchanged. I can't find the sheet showing the percentage of fluid renewal for the fz8 but I remember it and i'm not sure if even 3 will get you to 85-90% but that doesn't matter. I only do a single spill and fill on my transmissions. Have 335k on an all original 4l65e with changes every 70k or so. Still shifts perfectly.

 

[dishdude]

That's a complete waste of time and pricey ATF. One drain and refill is all you need.

 

[JavierH19]

That's a complete waste of time and pricey ATF. One drain and refill is all you need.

Agreed. 50% exchanged every 30k is just fine. Better to save both the extra labor and fluid to do it more frequently instead. It's more productive.

 

[paulo57509]

It doesn't take much driving to get new/old to mix.

Two D&R's are enough. According to the dilution calculator I found:

 

[Deleted member 89374]

The ZF 8-speed in our Q5 holds around 9L total and 4.5L can be drained out at once. I plan on doing three drain/fills to get to around 85-90% new fluid.

How many miles do you generally need to drive to get the new and old fluid mixed?

I want to drive it sufficiently enough to not be draining out the new fluid. Normally I would give it a week between changes, but I'm constrained by time as I am borrowing a friend's lift (2hr hours away) to do this trans fluid/filter change.

If you look through my posts, I have changed ATF on numerous transmissions, includin ZF 8 Speed.
If you have an electronically controlled thermostatic valve that opens at a fiven temperatured, then you need to drive it until you reach that temeperature so fluid can circulate through the entire system. Otherwise, a nice 5 to 10 mile drive should do it. I do a minimum of 3 drains and fills as well, especially when changing ATF formulations.

 

[weaponoffreedom]

If you look through my posts, I have changed ATF on numerous transmissions, includin ZF 8 Speed.
If you have an electronically controlled thermostatic valve that opens at a fiven temperatured, then you need to drive it until you reach that temeperature so fluid can circulate through the entire system. Otherwise, a nice 5 to 10 mile drive should do it. I do a minimum of 3 drains and fills as well, especially when changing ATF formulations.

Changing formulations is a good point to the idea of the complete exchange of fluid. Not mixing brands, even though all may meet the spec, is not a good idea especially in a transmission. You are a pretty smart dude

 

[Hall]

I do a minimum of 3 drains and fills as well, especially when changing ATF formulations.

Changing formulations is a good point to the idea of the complete exchange of fluid. Not mixing brands, even though all may meet the spec, is not a good idea especially in a transmission.

The amount replaced is 100% theoretical though. It's just based on a math formula. No one can prove you're removing "old" fluid. Once new fluid is added, it's 100% mixed with old fluid and any subsequent changes are removing new fluid.

These calculators - and I use them myself - just make us feel good about what we're doing/replacing.

 

[weaponoffreedom]

The amount replaced is 100% theoretical though. It's just based on a math formula. No one can prove you're removing "old" fluid. Once new fluid is added, it's 100% mixed with old fluid and any subsequent changes are removing new fluid.

These calculators - and I use them myself - just make us feel good about what we're doing/replacing.

Agreed and 100% correct. The law of averages thing.

I have wondered.....if mixing oils is in fact bad or less "good" than using a singular brand.

 

[atikovi]

That's a complete waste of time and pricey ATF. One drain and refill is all you need.

You have no idea how old or dirty his fluid is. If you can change out only 50% of the fluid at once, it's going to take a MINIMUM or 3 changes to even see an improvement if the existing fluid was old and dark. Even if you have to do it 5 times, that's still cheaper than a hard repair.

 

[dishdude]

You have no idea how old or dirty his fluid is. If you can change out only 50% of the fluid at once, it's going to take a MINIMUM or 3 changes to even see an improvement if the existing fluid was old and dark. Even if you have to do it 5 times, that's still cheaper than a hard repair.

It's a ZF 8 speed, it'll run forever on the factory fluid.

 

[atikovi]

So you actually believe transmission fluid lasts for the life of the vehicle?

 

[Chris142]

5 minutes

 

[leadcounsel]

I'd run any necessary calculations to ensure MOST of the fluid is new, it seems like about 3-4 swaps. ATF is so cheap it's not even a consideration on cost. Transmissions are on the other hand so expensive losing one can total the car. 4 Spill and Fills in short succession costs, what, $100? And needs to be done only a few times in the life of the car. This is a no brainer. Do a bunch on a new/used car, and then do 1 every 50k miles or whatever is suggested. You're talking maybe $500 on the life of ownership.

 

[wlk]

I do 3x drain/siphon and fills a couple hundred miles apart on all used vehicles I buy. Reasoning for me is adding the new fluid may help clean some and I like to clean up things slowly. Besides a couple hundred miles is only a couple weeks for me. On the last fill if compatible I add the appropriate amount of Lubegard Red. Then I do a drain/siphon every 30k from them on- w Lubegard Red if applicable. Has worked well for me for a long time.

 

[The Critic]

It's a ZF 8 speed, it'll run forever on the factory fluid.

Exactly. Design flaws or usage conditions are what kill transmissions. Not fluid changes….unless you fail to observe the OE interval.

 

[ctechbob]

It's a ZF 8 speed, it'll run forever on the factory fluid.

Except that ZF Themselves recommend something like a 60K change.

"Automatic ZF transmissions are filled with our specially developed ZF-LifeguardFluid transmission oil. At very high operating temperatures, oil ages faster than under normal conditions. Depending on driving style (e.g. sporty driving or lots of high-speed drives), ZF Aftermarket therefore recommends a transmission oil change every 100,000 km (62,000 Miles) or after 8 years at the latest."

How to Change the Transmission Oil on a Passenger Car

Transmission oil change

aftermarket.zf.com

Always found this article interesting. Maybe @The Critic could do this experiment on his Dodge:

Gears Magazine - The ZF 8-Speed Transmission Fluid and Filter Change

Changing transmission fluid after the vehicle is out of warranty is important for the life of the transmission. The issue of helping the customer understand that their vehicle’s transmission needs servicing is something different. Especially when we’re talking about the ZF 8-Speed. The dealer...

gearsmagazine.com

 

[Marcozi]

To fully replace all of the ATF find a shop that will perform a fluid exchange. This uses the pump in the transmission (this pump sends fluid to the cooler) to pump out old ATF and pump in new ATF.

"Lifetime fluids" was a marketing ploy, and not a maintenance philosophy.

 

[John105]

A mile is fine. But 3 drain and fills is unnecessary. Two is enough because of diminishing returns on the fluid exchanged. I can't find the sheet showing the percentage of fluid renewal for the fz8 but I remember it and i'm not sure if even 3 will get you to 85-90% but that doesn't matter. I only do a single spill and fill on my transmissions. Have 335k on an all original 4l65e with changes every 70k or so. Still shifts perfectly.

Agree with the mile.

I can’t find it but I recall from memory on my Lexus. % old remaining with each drain and fill looked like this.

55%
28%
19%

3 drain and fills left about 1/5 old fluid, so the conventional wisdom was 3x.

On my wife’s GM after 2 it was really pink and I never found any chart so I went with 2.

 

[rav]

I too have tge ZF 8 speed in our X5. I do a drain & fill @ 60k, then again at 10-15k. This will refresh your current fluid, to get rid of clutch material particles & replenish due to heat wear on the fluid. If you buy your fluid from FCPEURO, they will honor their lifetime warranty.