8 speed fluid change-level the truck or level the trans?

[g2020]

The dude in the video is ‘partially correct’ suggesting to check the levels directly related to thermostatic bypass valve (TBV), but this, in my best speculative uneducated suggestion should only be done when and if the cooler is (for what ever reason) is flushed out, repaired or replaced and is emptied or oil volume in the cooler was altered from some repair. It doesn’t require this “extra check” if the cooler is full to begin with and depending on temp (I think it’s 75F) is when it opens to cycle through the cooler and transmission.

Once cooling cycles are done as TBV cools and closes, that system remains full until the next temperature spike, when it’ll open and oil will flow around again.

For anyone doing just a pan drop, the component is cold, the TBV is closed and will remain full and that level doesn’t change and it’s “fullness” doesn’t change the levels at transmission temp one settles on between 86-122F when fill plug is reinserted and at 86F, the TBV is open and flowing around anyway.

For this guy to assume we all need to check levels later because of the TBV issue would be the same thing if he felt we should recheck because the torque converter empties out when we do a pan drop and we all know that doesn’t happen.

So I think it’s all moot unless levels need to be rechecked because cooler was drained out for repairs.

Update on 2026-06-09:

After careful review of the ZF process document (see first attachment to this post), here are the findings:

1. An ATF level check, as described in Section 12 of Pan Drop Instructions, is a necessary part of the pan drop process, and is completed after the vehicle has cooled off overnight
2. During a pan drop, it is necessary to 1) overfill the transmission with 0.5 liters of ATF as shown on page 4/6 of the ZF document (see first attachment to Pan Drop Instructions), 2) drive the vehicle until the Thermostatic Bypass Valve (TBV) opens, and 3) park the vehicle & turn the engine off to allow the vehicle to cool off overnight
   1. ZF recommends an overfill of 0.5L for any vehicle in which a transmission oil cooler is present
   2. TBV opens at Trans Temp between 140°F and 158°F (between 60°C and 70°C), and Trans Temp must not exceed 167°F (75°C) when driving and then parking vehicle at the end of day #1 of the pan drop process
   3. Trans Temp at which the TBV opens is above the temperature range in which the A) timed shifting sequence and B) ATF level check are completed on day # 2 of pan drop process (between 86°F and 122°F, or between 30°C and 50°C); in other words, the vehicle must be driven at the end of pan drop day #1 to open the TBV
   4. At 12:03 in this video, the presenter discusses (separate) guidance from ZF on the TBV & transmission cooler lines
      
      
   5. Never do a transmission flush

Original reply:

Nice catch from a guy who's done no fewer than seven pan drops. You would have noticed a fluid level drop.

Let's confirm these temps and come back to this.

I think that Weber State should nominate you to be a guest speaker at the annual association conference.

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[ShadowsPapa]

So the pro is wrong and a random person is right?
And if the youtube video is correct you tell people don't worry about a recheck?

 

[ShadowsPapa]

I've seen mine up to 220f while climbing up some switchbacks. Normal driving is 190-200 on mine.

I don't know where people get the idea that any number over 200 is bad for everything from oil to coolant to transmissions. Do they just grab it because it's a nice round number, a feeling, or they read it somewhere, or is it numerology?
Old stuff like pull a cable to check your alternator (NO! NEVER do that)?
Pulled out of a hat?

This thread has gotten unreal. No need to check the level again, 200 bad, cold good.
Ignore the fact that "depending" on circumstances when that pan is dropped, fluid may drain from lines that aren't opened again until the cooler is out of bypass, and no, it's not about synthetic vs blend.
As with oils, some blends can tolerate heat better than some synthetics.

But let's try to out think experienced engineers with our own explanations.

As they say, it's your jeep, your transmission. But the level of faulty info on the internet, even forums, is scary.

 

[Maximus Gladius]

Nice catch from a guy who's done no fewer than seven pan drops. You would have noticed a fluid level drop.

Let's confirm these temps and come back to this.

I think that Weber State should nominate you to be a guest speaker at the annual association conference.

Well being nominated is going to far, if I could bring anything to this table it would be 'we all need to be a critical thinker'. For some of us (and even for career long master techs) critical thinking is impossible, we can even throw in some engineers. Look up failed structures like falling bridges and buildings, retaining wall failures, downed planes, trains and automobiles failures on engineered stamped designed and built things that killed people. @ShadowsPapa, you give too much credit to the "engineer" that obviously knows better, and zero credit to the non classroom educated critical thinker that can think outside the box (not doing damage) but thinking outside.

 

[ShadowsPapa]

Comparing bridges and aircraft to transmissions made by the millions, evaluating failed units from the real world, and lab testing .......

If there is a one in 20 chance of the fluid being low after running at full temperature through all 8 gears and opening the cooler on the road with engine running that it may need more fluid, experience tells me, check it again.

On one hand we have it said level is critical, then almost the same sentence, no need to check it again.

Millions of transmissions of many makes go over 200 or 210 with companies, and tow people, saying fine, and I and others see those temps fairly often, that, I'm not worried about. It's not severe service.

People here accuse me of being too much a critical thinker, I know I utilize perceptual reasoning more than most of the population.

 

[Maximus Gladius]

I don't know where people get the idea that any number over 200 is bad for everything from oil to coolant to transmissions. Do they just grab it because it's a nice round number, a feeling, or they read it somewhere, or is it numerology?
Old stuff like pull a cable to check your alternator (NO! NEVER do that)?
Pulled out of a hat?

This thread has gotten unreal. No need to check the level again, 200 bad, cold good.
Ignore the fact that "depending" on circumstances when that pan is dropped, fluid may drain from lines that aren't opened again until the cooler is out of bypass, and no, it's not about synthetic vs blend.
As with oils, some blends can tolerate heat better than some synthetics.

But let's try to out think experienced engineers with our own explanations.

As they say, it's your jeep, your transmission. But the level of faulty info on the internet, even forums, is scary.

Breathe..... You'll be alright. I understand these things get you triggered. Ive never made black and white statements as you're forcing on me. Let's clear the air ...

What makes me tick or what causes me to "monitor or watch" my temp gauges is when something I do is a 'cause and effect' and what is "normal" becomes "not normal". Something changes in the temp department, ...so I watch and see.

You blame me for "old old old thinking". Your experience is what you know from old practice you became most excellent in. We all know that . You never became an "engineer" (that I know of) but you sure could put a room full of engineers to shame quite easily if you had too.

You once told me you don't have any experience with these new transmissions, your experience and career was with the old ones. You told me this when I was going through my first dramatic horror story and for some reason you and I were discussing it. You even invited me down to your place to show you how to do a pan drop if I was ever in your area, but sadly now,...I'm just one that gives faulty info and freaks out. Too bad...

I don't come up with my own conclusions out of needing to feel good but have support and much discussion with the oil analysis lab tech (40 year tech) I can go in and see anytime I feel like it and he will show me the lab's computer diagrams and printed graphs that are so far above my knowledge of understanding but not too much it's impossible to see or implement a "good proactive practice" when I see it or discuss it with the lab tech. These non status quo processes are born here, lab data compared and action taken. You see what I do, not done out of some internet idea or from freaking out.

Good practice ISN'T what others see their components do when hauling or pulling heavy. Claiming "my component can do (220-230+) isn't just some badge of honour because it did it, its understanding or as I do, question the "cause and effect" of such temps one time or multiple times. Its in the investigative realm of understanding this cause and effect that will either make you respond, or not, for what's best for the component.

It's not about "I can do 230F+", it's do I want to not deal with that, I'm deciding because I did it, I will forget about doing anything about it, "other oil manufactures products are good to 300F so I'll lump the 8/9 Speed into that category too with absolute blind faith".

"Old thinking and practice" is to maintain old practice and carry on like we've all done since forever. We have the data points, transmission characteristics of doing nothing, so we all want better but will not (stubbornly) do anything different. The definition of insanity is to do the same thing over and over, expecting a different result. If we want better results, we have to change something.

 

[Maximus Gladius]

Comparing bridges and aircraft to transmissions made by the millions, evaluating failed units from the real world, and lab testing .......

If there is a one in 20 chance of the fluid being low after running at full temperature through all 8 gears and opening the cooler on the road with engine running that it may need more fluid, experience tells me, check it again.

On one hand we have it said level is critical, then almost the same sentence, no need to check it again.

Millions of transmissions of many makes go over 200 or 210 with companies, and tow people, saying fine, and I and others see those temps fairly often, that, I'm not worried about. It's not severe service.

People here accuse me of being too much a critical thinker, I know I utilize perceptual reasoning more than most of the population.

I've never said "no need to check it", you are throwing that at me. My practice is to check it, maybe a week later or so. But as I keep doing my annual pan drops and "checking" some time after, the level hasn't changed so it becomes less and less on my radar but will be done if I feel I have 30 minutes to give to it.

 

[ShadowsPapa]

My practice - every transmission I've ever rebuilt or had open for any reason -

Run it through the gears on the lift. Check fluid, take for test drive.
Bring it back, check the fluid again.

With the type (back in the day) that had band adjustments - do them again because you just flexed them, got everything wet and working against the drum, double-check the band adjustments.
(not a thing in many years, that's going way back)

By taking it for a highway drive, and through town a few blocks, I made sure every servo, every accumulator, every clutch pack was exercised, full of fluid, and the whole valve body had been utilized.

Necessary, probably not, but it sure kept my comeback record at 0 and the boss appreciated that his customers kept coming back.

It's your choice - do it or don't do it.

Fluid temps - also your choice, but please don't suggest or make others are burning things up or really need to do a change if they hit 210 or even 220 for a bit.

Here's something I find interesting about the transmission temperature readings on these - watch that temperature REALLY CLOSE, display it in front of your nose in the cluster.
Now pay attention to that as it changes gears, up a bit of a hill, back down, upshifting and downshifting, on the flat and so on.
Mine will jump and drop temperatures as it shifts. It's like ok, now we've got some warmer fluid coming through past that sensor then suddenly, it shifts again and the temp drops a few degrees.
I watched it fluctuate between the 170s and 180s just as it changes gears and so on.

However, as I know that in the past with "radiator cooled ATF" you were hitting engine temps with that fluid, 200-210 is nothing at all.
Heck, my Comanche used to run 215 or better - imagine fluid going through a radiator cooler if it had an automatic.

Do whatever makes you feel good, but I wouldn't use the word "prudent" for a fluid change because of 200-210 or even 220 - others look at that, all of the lurkers and people searching for answers and will say, OMG, mine hit 210 for a while today, they are saying it's prudent to do a fluid change now.

Yes, people will take it that way.

I'm officially done with this thread, unwatching and not coming back. It's gotten too messy with speculation and that sort of thing.

 

[Vtur]

New silent code. No members are allowed to respond to @ShadowsPapa after page 2 of any threads.

 

[Maximus Gladius]

Do whatever makes you feel good, but I wouldn't use the word "prudent" for a fluid change because of 200-210 or even 220 - others look at that, all of the lurkers and people searching for answers and will say, OMG, mine hit 210 for a while today, they are saying it's prudent to do a fluid change now.

Yes, people will take it that way.

I'm officially done with this thread, unwatching and not coming back. It's gotten too messy with speculation and that sort of thing.

Too bad you left the building. You have much that is good. For all the ones @ShadowsPapa says will panic and feel because I said the word “prudent” to doing a pan drop because we saw our temps 200+, I need to clarify because this key thing CANT be guessed because we think these 200+ temps are just fine because we’ve seen them. It’s bigger and more important than that.

Firstly (I didn’t come up with this, ZF did) that ‘it can make sense to change the oil at shorter intervals if one doesn’t know the history of the vehicle or if higher temps are reached’ is stated by ZF

I read that some time ago and the word “prudent” came to mind so that’s what sticks out for me. So allow me to change that word for the phrase “it would make sense” to do this. For anyone reading all I’ve said and is panicking because I said that word, I hope changing it to “it makes sense” provides some relief.

The topic of “what temperature is hot” and when does it make sense to change the oil can only be clarified, not by guessing or what normal practice is for you or what’s been long time accepted by engineers and red seal mechanics and experts that express what they know based on feelings or classroom regurgitation.

“Hot” or what is “too hot” is when oxidation is formed. Oxidation will then break down the additives and also form varnish deposits. Measurable Oxidation can only be detected by the lab. If oxidation is measurable, “hot” or “too hot” was reached.

Oxidation is a cancer. How serious do we look at it? Is a little cancer ok and do we want it in there and is doing frequent or annual pan drops going to cause harm?

 

[LouisvEarlleJT]

To answer the question about if I measured what I took out. I did but didnt go by that, more just to make sure I was in that window of refill. The fill method negates putting in what you take out. My refill amounts are around 5.5 quarts as other people report though.

Just curious, how much was drained?

 

[Stan H]

I think shadowpapa is right on transmission temps. 200 is the mean on the digital gage.

Hot days over 80F-90F mine runs 195 cold days 172-176 200 I can see on the highway running 70 uphill and its only for a minute then it will pull back down 195-197 I don't think 200 hurts em. If it did they would said something about it by now .

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