Complete ATF Change...Best Way?

[AdmiralYoda]

Getting close to time to change my ATF in the 8L45 in my GMC Canyon. What is the best way to swap as close to 100% of the fluid out without going to the dealer? A pan drop and filter change only gets about 50-60% of the fluid.

Once upon a time on an older vehicle I didn’t care too much about I hooked a clear hose to the outlet line that went to the radiator. I started the engine and at the first sign of air bubbles (trans pump had sucked the pan almost dry) I shut the engine off and added the same amount of fluid that got pumped out back into the transmission. I did this 3-4 times and 100% of the fluid was changed over to brand new stuff.

This still a good idea? Or an I just better off draining the fluid out of the pan a few times? Thanks!

 

[John105]

I just did 2 drain/fills with the Enclave and it was pink. I don’t know the calculation on how much old is left (the Lexus is 55/31/19), but I get the feeling that just 2 is way better then 31% old and I didn’t feel the need to do a 3rd. I had to get a new drain plug that comes with sealant as I didn’t know for sure what sealant to use and the plug was < $3 at rock…

Ps Dex VI seems expensive Walmarts house brand was $9.38 yesterday…I had stocked up on 2 cases around 2017 when it was about $5/qt full synth…

 

[PontiacHO]

I used an oil vacuum and pulled out all that I could. Refilled, drove, and repeat. Used 12 quarts over 3 separate processes.

 

[JavierH19]

The best way is to not try the best way. It's genuinely not worth the hassle to do multiple fluid changes and even 95% is kind of impossible. Just a spill and fill every 30k and you'll be set.

I do a spill and fill every 65-70k on my 4l65e which is less than half as often as i suggest, But these older transmissions don't run as hot as the new ones are forced to and they're more built for it. It has 335k miles and counting since i bought it new in 05 and she's still golden. Never replaced anything inside the transmission other than just the filter, that's it. I've towed occasionally as well.

 

[JHZR2]

Fortunately my MB cars have a drain on the pan and the torque converter. Thst gets a lot out.

If it were that important, I’d suction as much as I could from the pan via dipstick, run the engine a while, then do a pan drop. Notionally then you’d have 30%-ish new in there before the pan drop, do thst, maybe flush the cooler lines, and then refill.

I personally wouldn’t worry about the rest, if anything I’d do the next OCI a bit sooner.

 

[JavierH19]

Fortunately my MB cars have a drain on the pan and the torque converter. Thst gets a lot out.

If it were that important, I’d suction as much as I could from the pan via dipstick, run the engine a while, then do a pan drop. Notionally then you’d have 30%-ish new in there before the pan drop, do thst, maybe flush the cooler lines, and then refill.

I personally wouldn’t worry about the rest, if anything I’d do the next OCI a bit sooner.

I wish every automatic had a tc plug and a spin on filter. But the 8l doesn't have a tc plug which stinks. That's what makes multiple spill and fills wasteful on some transmissions.

 

[gman2304]

I used an oil vacuum and pulled out all that I could. Refilled, drove, and repeat. Used 12 quarts over 3 separate processes.

I do this on my 2005 4L60E once a year but siphon 3 to 4 qts each time. 239,000 miles on original transmission and takes only about 15 minutes with no mess. The pan has never been off and the fluid is bright red and transmission shifts great.

 

[hrv]

The best way is to not try the best way. It's genuinely not worth the hassle to do multiple fluid changes and even 95% is kind of impossible. Just a spill and fill every 30k and you'll be set.

I do a spill and fill every 65-70k on my 4l65e which is less than half as often as i suggest, But these older transmissions don't run as hot as the new ones are forced to and they're more built for it. It has 335k miles and counting since i bought it new in 05 and she's still golden. Never replaced anything inside the transmission other than just the filter, that's it. I've towed occasionally as well.

YUP.....KISS...Keep It Simple Stupid...

 

[Hall]

Getting close to time to change my ATF in the 8L45 in my GMC Canyon. What is the best way to swap as close to 100% of the fluid out without going to the dealer? A pan drop and filter change only gets about 50-60% of the fluid.

What mileage are you at ? If it has a drain plug, just drain and refill it every 30k miles. If the only way is to remove the pan, even doing that every 2-3 years (~30k miles ??) is pretty good maintenance.

 

[nobb]

The best way is to not try the best way. It's genuinely not worth the hassle to do multiple fluid changes and even 95% is kind of impossible. Just a spill and fill every 30k and you'll be set.

This. It's not that big of a deal if you're not getting 100% of the fluid out. The fact that you're even doing a D+F puts you ahead of 90% of the population.

 

[jetman]

Getting close to time to change my ATF in the 8L45 in my GMC Canyon. What is the best way to swap as close to 100% of the fluid out without going to the dealer? A pan drop and filter change only gets about 50-60% of the fluid.

Once upon a time on an older vehicle I didn’t care too much about I hooked a clear hose to the outlet line that went to the radiator. I started the engine and at the first sign of air bubbles (trans pump had sucked the pan almost dry) I shut the engine off and added the same amount of fluid that got pumped out back into the transmission. I did this 3-4 times and 100% of the fluid was changed over to brand new stuff.

This still a good idea? Or an I just better off draining the fluid out of the pan a few times? Thanks!

yes, or 2 or 3 drain and fills

 

[dubber09]

Easiest are usually D/F multiple times but all in all - time consuming and can get expensive and wasting ATF.
I prefer D/F and then replacing rest of old ATF while draining via ATF cooler line. One time service replacing 100% fluid.

 

[SC Maintenance]

Once upon a time on an older vehicle I didn’t care too much about I hooked a clear hose to the outlet line that went to the radiator. I started the engine and at the first sign of air bubbles (trans pump had sucked the pan almost dry) I shut the engine off and added the same amount of fluid that got pumped out back into the transmission. I did this 3-4 times and 100% of the fluid was changed over to brand new stuff.

This is called a poor man's flush, and its the second best way.

The best way - IMHO - is a a poor man's flush with a helper - the helper starts the engine - you pour fluid down the dipstick at approximately the rate fluid is coming out into the bucket. The helper is there to stop if you get behind. You keep this up until the fluid coming out runs clear, button it back up, and add / delete fluid until your at the correct level.

However I agree that in most cases a drain and fill is sufficient.

 

[Passport1]

Get an oil suction unit. Suction out a measured amount and refill with the same amount. Do this several times at a reasonable distance, say 100 miles. Record the amounts in a spread sheet with total capacity as the base. You will get to 80- 90% pretty quickly.

 

[atikovi]

It's not that big of a deal if you're not getting 100% of the fluid out.

By that argument, just draining the motor oil without changing the filter would be ok? I don't think so. Doing a drain and refill every 30,000 miles is great if started since new, but op didn't mention that as the case. Assuming he hasn't changed it before and he isn't the original owner or it's been 100,000 miles since it was last changed, a pan off drain with filter replacement is the minimum service I would do. Ideally followed by drain and refills until the fluid drained looks as clean as the fluid in the bottle.

 

[SC Maintenance]

By that argument, just draining the motor oil without changing the filter would be ok? I don't think so. Doing a drain and refill every 30,000 miles is great if started since new, but op didn't mention that as the case. Assuming he hasn't changed it before and he isn't the original owner or it's been 100,000 miles since it was last changed, a pan off drain with filter replacement is the minimum service I would do. Ideally followed by drain and refills until the fluid drained looks as clean as the fluid in the bottle.

I actually agree with you analysis at 100K, however the comparison to engine oil isn't accurate simply because there are no byproducts of combustion in a transmission. You have wear particles and sheared fluid and used up detergent, but the fluid itself isn't dirty - hence why OEM's can get away with claiming lifetime fluid.

If it had a dipstick then I would do the Poor man's flush.

If it doesn't I would do multiple drain and fills.

Either way you need to drop the pan and change the filter - if yours has a filter, many don't anymore.

 

[AdmiralYoda]

Thank you for all the feedback! The truck is a 2021 GMC Canyon and has 21k miles on it and I am the second owner. The severe service schedule says change the fluid at 45k (might be 47.5k). With the questionable reputation on the 8L series transmissions I wouldn't mind putting some fresh oil in there for peace of mind. Though they supposedly had all the fixes in place in 2020 for the 2021 model year.

These trucks didn't come with dipsticks so I have to pump it out from underneath where the dipstick plug is...or just D+F which is probably what I'll do, and throw a new filter on there for the heck of it. I will be installing a dipstick while I'm at it for future ease of maintenance.

Fun fact... these transmissions do not have an internal bypass thermostat, so all the fluid goes to the radiator and external cooler if equipped 100% of the time. On a 90 degree day it takes a half hour to reach 120F on the highway and the highest I have seen the trans temp is 135F after some spirited driving. In the winter these transmissions take forever for the torque converter to lock up because the fluid needs to be 50-75F.

Some transmission service magazines have theorized that the relatively cold fluid allows moisture buildup over time and degrades the additive pack.

 

[xmanjeff]

This is called a poor man's flush, and its the second best way.

The best way - IMHO - is a a poor man's flush with a helper - the helper starts the engine - you pour fluid down the dipstick at approximately the rate fluid is coming out into the bucket. The helper is there to stop if you get behind. You keep this up until the fluid coming out runs clear, button it back up, and add / delete fluid until your at the correct level.

However I agree that in most cases a drain and fill is sufficient.

i like to do this , disconecting the cooling line going back to transmission until you see god fluid coming out

 

[tnt_motorsports]

FWIW I recommend an oil extractor pump and do the process twice if it bothers you that much. Keep in mind that a 50%+ exchange in fluid is better than many cars that go to the salvage yard will see.

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Just my $0.02

 

[nobb]

By that argument, just draining the motor oil without changing the filter would be ok? I don't think so. Doing a drain and refill every 30,000 miles is great if started since new, but op didn't mention that as the case. Assuming he hasn't changed it before and he isn't the original owner or it's been 100,000 miles since it was last changed, a pan off drain with filter replacement is the minimum service I would do. Ideally followed by drain and refills until the fluid drained looks as clean as the fluid in the bottle.

Engine oil is a completely different application with different byproducts. Obviously it would be preferrable to be able to drain out the entire ATF system, but in many cases there's still 30-50% of the fluid stuck in there and it requires substantially more effort trying to get that out.

If it was a super dirty, unmaintained system, then yes I could see a case for doing a few drain & fills to clean it up. But on a decently maintained system it's not necessary.