what signals a need to change ATF?

[Dragfluid]

Including the Ford 6R80 & GM 8L90.

The 8L90 is due to the original fluid being hydroscopic, like brake fluid. The official fix is the flush it with the new fluid. If no more shudder, it's fixed. If it was let go too long and shudders after the flush, it gets a converter.
Wasn't sure about the 6R80 and this issue, but I've been out of the trade for 3.5 years and probably forgot. Looked in some notes and it's there. New fluid and Shudder Fix.

 

[clinebarger]

Had a 2022 Silverado 2.7L/8L90 in recently with TCC shudder & fresh fluid fixed it....This is long after the update to blue label M1 Dexron HP.
Had a few 2019/2020 Silverado 5.3L/8L90 come in right around 100K & fresh M1 HP fixed those.

Either the updated M1 is also hydroscopic or the fluid is degrading like you discussed?

 

[Sumboodie]

I always dump fluids and filters on new to me stuff unless I can trust it's been done.

 

[Hall]

Including the Ford 6R80 & GM 8L90.

Bought a '12 Honda Civic and at a very specific throttle, speed, and gear, it would shudder. Changed the fluid (drain and refill) 1x and it solved it. Waited another few thousand miles and did it a 2nd time just for good measure.

 

[Sequoiasoon]

New AT fluid and filter in father-in-laws CRV got it back shifting correct again from neglect. It stayed working well for another probably 50k until 2nd gear didn't want to anymore. Tried some fluid changes, solenoids, checked screens. Those didn't help anymore at that point. It did have almost 270k on it when 2nd went out.

What signals change? If you know that your tranny temperature gets too hot where fluid will break down and normally runs about 50 degrees cooler. Hauling an empty 5x8 enclosed trailer (840 lbs) in slow traffic for 2 hours, followed by lots of stop signs and hills. I could smell that whiff of tranny fluid too hot at the stop signs. '19 Pilot EX-L 6 speed transmission. It's getting 30k changes at the dealer and not before. That is about 7000 miles from now. Dealer acknowledged my issues and fluid concerns and also don't feel it will last but with no trouble codes, not much they can do. HondaCare Warranty is still in effect for 18 more months.

I posted other times on it and how many changes I had done. The Honda DW-1 at least in mine gets very dark brown quickly even when I'm not towing. My towing is that trailer above 2-3 times per year, about 100 miles, each way. Even fully loaded with kids college stuff is only about 2000 lbs on scale.

I bought a Scangauge 3 to see if for some reason my PID was wrong with OBD fusion. I didn't get back to this temperature but did get to 220F and SG3 matched OBD fusion. Advantage for SG3 is it also shows TC slip % and rear differential temperatures. I haven't found those PID's yet on the forums.

 

[D60]

‐------------------
Hygroscopy is the chemical term for a substance's tendency to attract and retain water molecules from the surrounding environment. The word comes from Greek and literally means "tending to retain moisture".
----------------‐-------------------

I dunno why, but it's a G, not a D. Hygroscopic. I guess the Greeks get it.

 

[Dragfluid]

New AT fluid and filter in father-in-laws CRV got it back shifting correct again from neglect. It stayed working well for another probably 50k until 2nd gear didn't want to anymore. Tried some fluid changes, solenoids, checked screens. Those didn't help anymore at that point. It did have almost 270k on it when 2nd went out.

What signals change? If you know that your tranny temperature gets too hot where fluid will break down and normally runs about 50 degrees cooler. Hauling an empty 5x8 enclosed trailer (840 lbs) in slow traffic for 2 hours, followed by lots of stop signs and hills. I could smell that whiff of tranny fluid too hot at the stop signs. '19 Pilot EX-L 6 speed transmission. It's getting 30k changes at the dealer and not before. That is about 7000 miles from now. Dealer acknowledged my issues and fluid concerns and also don't feel it will last but with no trouble codes, not much they can do. HondaCare Warranty is still in effect for 18 more months.

I posted other times on it and how many changes I had done. The Honda DW-1 at least in mine gets very dark brown quickly even when I'm not towing. My towing is that trailer above 2-3 times per year, about 100 miles, each way. Even fully loaded with kids college stuff is only about 2000 lbs on scale.

I bought a Scangauge 3 to see if for some reason my PID was wrong with OBD fusion. I didn't get back to this temperature but did get to 220F and SG3 matched OBD fusion. Advantage for SG3 is it also shows TC slip % and rear differential temperatures. I haven't found those PID's yet on the forums.

View attachment 282927

220F is too **** hot!

 

[TomYoung]

Changing the fluid and filter every 30k miles for any automatic transmission will ensure you get the most life out of it. If you’re towing, check the transmission fluid every 5k miles, and make sure it doesn’t smell funny. If it starts to smell slightly burnt or acidic, just change the fluid, because if it smells funny, it means the fluid is starting to break down from heat, and it can also mean your clutches might be starting to slip slightly. You never want to get to this point and then try to change the fluid, because damage has already been done if fluid smells burnt or acidic.

A/T fluid has to lubricate all the planetary gears, bearings, clutches, it also has to remove heat from internals, and also maintain the proper viscosity to allow proper fluid pressure for gear changes, and has to maintain proper viscosity which allows proper pressure to hold gears.

Just change the fluid every 30k miles. Cheap insurance. No reason to really use any boutique AT fluid. Just change the fluid often enough with any good fluid that meets your transmission’s spec, and you’ll be fine.

I just do not see a reason why we should go 60k miles or even longer when good fluid and filter is very affordable and easy to swap out compared to a transmission rebuild or a replacement. Automatic Transmissions are incredibly complex and intricate, and to get it rebuilt or replaced will cost an arm and a leg. Frequent fluid changes are all we DIY people or just people who care about their vehicles can do to make it last.

This is solid advice, although for some vehicles, 30k intervals might be a little punishing. Definitely tighten what the manufacturer recommendation is, but most cars out there will go 50k on transmission fluid.

 

[TomYoung]

Fluid changes on A/T with unknown history, when fluid change would be good and when it would be detrimental?

I’ve already done a thread on my specific vehicle and the consensus was that I could probably do a drain and fill for better shifting, longevity, etc etc. More generally, is there a telltale way to know that changing your ATF would reap benefits or if it’ll cause neutral soup? This is without dropping the pan so really only by examining fluid scent/colour on the dipstick. Or maybe an extractor and inspecting fluid in a jar

I would state this question differently. The question is, essentially, "When should I replace my transmission fluid?" Then gets into a discussion on the state of the fluid and how it can be tested. As other responders have noted, the transmission is a complex, expensive system that should be treated well. I think we all know after spending some time on BITOG, you want to change your fluid when it is still clean, still working perfectly. If you send clean, nice fluid that has delivered, say, 40,000 miles, off to recycling, you should be happy. Trans fluid is a little different than motor oil in that it sometimes does not show its age by capturing combustion products, and may look new. There is never any detriment to swapping fluid, although I would allow that a 10k interval would be excessive. You can test the fluid, but why? It is certain that once you can smell or see a color that is untoward, once you suspect you are approaching "neutral soup," you have gone far too long. If you get some manufacturer that claims fluid is for a lifetime, reject that. I'd go with 80k, or less.

 

[SumGuy]

My "fleet" consists of 5 different Chrysler 300m's (2000 to 2004, one of each year). One I bought new in 1999, the others I've bought used about 5 years ago. They have the 42LE 4 speed automatic. I've only ever had the new one have a transmission oil change according to the book, the others I have no idea their oil change history. They all have between 100 and 200k miles on them now (two are maybe 80 - 90k). I can say the same thing about the brake fluid (ie possibly still original fluid in the cars that have not had their brake lines replaced).

Now I have been much more focused on the differential oil. I understand that on some cars, the differential shares the same sump, same oil as the transmission, where others separate the two. I have changed the differential oil, 70W90 gear oil is called for.