20K and ATF Degradation @ 65,000

The transmission is "sealed" but still vented to atmosphere, else your seals would leak anytime you change elevation or the barometric pressure changes. Atmospheric air has water vapor mixed in to it (not sure I know if anywhere that is 0% humidity), so moisture is constantly being introduced in to the transmission. The heat cycling of the transmission causes some of that moisture to condense, introducing water in to the case. The transmission fluid has additives in it to absorb that water, but those additives are in limited supply - once they are all used up they are all used up. BUT... water can be evaporated by means of introducing heat up to the boiling point of water, which can then be pushed back in to the air in the transmission case and vented to atmosphere. This relieves the additives of some of the water they have absorbed, freeing them up to absorb moisture that will continue to be introduced in to the transmission via atmospheric air and heat/cold cycles. However, if your transmission fluid never reaches water boiling temperature, the only tool at your disposal for removing moisture is the fluid itself, so it degrades faster and needs to be changed sooner.

The same principles apply to crankcase and engine oil. This is why short trips and particularly short trips at low temps qualify as severe duty for maintenance schedules.

Just food for thought...

Edit: Also, fluid that is thicker creates more cushion between parts, with the downside that it can create too much cushion between frictions and steels in the transmission. Fluid viscosity is spec'd very specifically so the the line pressures and piston apply areas are tuned to overcome that viscous cushion at certain rates and pressures. Increasing that viscosity can increase the clutch/steel engagement time (meaning it takes longer between the times the apply piston starts to apply the clutch to the steel, and when the clutch and steel mesh completely and lock together), causing more friction and wear between the two parts. Counterintuitive as it may seem, it's how it works...

 

Please quantify how much air is introduced to a 5.7l engine working at 1500-2000 RPMs, and to its transmission via breather hole and main seals over a course of, say, 30k miles? I'd expect it to be somewhere in the range of 10-20 orders of magnitude, but please go ahead with your calculations. Also quantify water vapor generation potency loss by driving ATF temp down from 195 to 165 F. I wouldn't further complicate it by mentioning a higher temperature at torque converter and presence of heat exchanger where ATF is heated closer to a coolant temperature, which is around 200F for your information, so any traces of water have sufficient time to evaporate. I wouldn't complicate it even further by mentioning that soluble gas won't just leave the fluid until its partial pressure in the full pressure of the air trapped in transmission is significantly less than its partial pressure in the fluid. Separation is not happening actively in the engine's crankcase where water is really present if there's no vacuum there and water vapors are not removed promptly, aka PCV is broken. This is how engine oil becomes watery even if it is heated close to water boiling temp.

 

You are welcome to quantify things for your own knowledge discovery trip. I think kids these days jus like to ask for the answer rather than discover things on their own..

 

When I went on a first date with my now fiancée, I asked if it was carpet or linoleum down below decks.

She said rather than tell me I should find out for myself.







A good time was had by all.

 

Is this conversation still about transmission fluid and ATF degradation or are we talking about something else?

I honestly don't care what you all do on the pinned vs not topic, but I recently bought a new chair, and it's leather, which means I'll be cooler sitting in it. Won't use it until after I get around to smearing WS on the seat cushion so it can withstand the swamp ass and thunder farts. Open to other ideas.

 

Proof or it didn't happen!

 

I don't want to see that! Yikes!

...and you know he'll do it.

 

It's not though. Water is a byproduct of the combustion process, that is what leads to moisture in the motor oil. Combustion is the reason engine oil changes are so much more frequent than transmission fluid, t-case or diff oil changes.

 

This is true. But it is not the only reason for moisture in the crankcase. Cars that have low miles still time out on oil changes whether they are driven or sitting; the oil doesn’t go rancid like cooking oil or anything silly like that. Cars sitting still creates condensation in the crankcase from temperature fluctuations and humidity in the air. Apparently that creates enough condensate to call for an periodic oil change based solely on time.

I’m not trying to tell anybody that they are wrong or a dumb dumb - I’m just illustrating some of the ongoing processes that affect vehicle maintenance and longevity.

 

Yea but if there is a penalty written into the maintenance book to change it more often then there is likely a penalty written into the code for degradation.

 

Solid advice from a Toyota mechanic, Thank you Dave.

 

Do you say ATF degrades more quickly when heated slightly less? And what do you mean exactly by degradation here? Heat breakdown or friction wear?

 

here's what I'm presently pondering...

no cooler - I ran 220's unladen - flat road. sometimes - 240 in Africa-type Houston summers.

cooler un-pinned- I ran 195 no matter what the weather.

cooler pinned - I run 165

my quandary -
It would appear the cooler never opened given the above data
or if it did, it opens and closes a lot. you would think that once the thermostat opens, the trans temp will drop to 165.
but when it's un-pinned it stays very stable @ 195.. explain that.

and (pinned open) it also appears that the Trans heating up has a strong correlation to the engine temperature, because once I've been driving for say 15 minutes....the trans is stable @ 165-ish - regardless of ambient temp.

I don't tow, so I can't speak to that variable.

wait - I did tow a small covered trailer from Houston to Belton...the trans rose & stayed @ 201 with unpinned cooler. explain that one.


and for the cherry on top - I use Valvoline maxlife. I've done 2 D&F's with 80k miles on it.

 

I can't explain why yours is staying at 165F, other than the cooler is really effective at heat transfer. I keep mine unpinned and let the thermostat open and close. It opens around 195F and temperature drops to 185F and hovers around 185F-195F. Before I was well into 220F without the cooler. The fluid is always "warmed" by the warmer puck, regardless of whether or not it is pinned. 165F does seem really low though.

 

The thermostat can be in a mid position and trans fluid can flow to both the ambient cooler and the liquid to liquid cooler/warmer. There is no on/off like operation, it's variable. Think of it the same way your engine thermostat works. Would you ever remove your engine thermostat to allow it to run cooler? Of course not.

 

truth be told...they make a 160degree TS for the tundra & I contemplated that....but that's a discussion for another time.

 

Do you monitor engine oil temps?

Agreed with @Ruggybuggy that the thermostat isn't necessarily an on/off switch. What I have noticed since running a cooler (I do not pin the T-stat open) is that my transmission pan temp tracks engine oil temp at ±<2ºF. This is a function of the internal oil puck. This is how the transmission gets up to operating temp. Pinning the T-stat open simply prolongs this process because the cool air flowing over your radiator works against the warm engine oil flowing through that puck. And maybe it prevents it from occurring altogether if you're just doing easy short trips.

I guess my main point is, if your engine oil doesn't get up to 195ºF-ish, then I don't think your transmission will get there, either.

The benefit of the external cooler I observe is that the pan temps never run away from engine oil temps like they did before. And I'm a broken record on this part of it: when this transmission was designed, EVERY tow package-equipped truck came with one. I just want mine to work as originally designed, even if the 2019-2021 trucks have different lockup programming.

 

The other part to consider is what fluid is being sent to the thermostat. It appears as though the fluid exiting the torque converter goes straight to the thermostat/cooler, which makes sense. Send the warmest fluid directly to the cooler.

When im on the highway, 80mph, TC locked in 6th gear, i'll see 194F pan temp and TC outlet temp. If i go up a slight rise, TC unlocks, TC outlet temp may jump to 200-205F, pan temp does DOWN. I can watch as the pan temp will cool down to upper 180s. TC locks again, temps both settle back at 194.

If i'm sitting stationary in gear, TC outlet temp will be mid 190s. Pan temp will cool to 177F-ish.

Thats why i installed a giant trans cooler, no need to pin the thermostat. Just drive the thing.

 

you make a good point...I do monitor engine temp via SG3, and it is a normal 195-ish. which is part of my temp delta conundrum.

I would have bet a $1 that the trans would rise to 195 with it pinned....it would just rise slower.

on my recent 400 mile road trip, the trans never rose above 170. ponderous.

once we get some colder air here in Houston...we maybe might get to 32...i wonder if it will still stay at 165-ish. If so, I'll unpin.

but the real mitigating factor is getting under there and removing the cat shields. not fun.

 

I guess my conclusion is that your cooler overpowers the internal puck with the T-stat pinned.

I'm running one of the original Hayden kits that Genuine Cooling Systems offered back in Fall 2020. I understand that various kits since then have run larger radiators.

If I wanted to be really paranoid, I would be concerned with the moisture issue over the long term if my transmission never got up to the temps at which water vaporizes.

 

How are you monitoring oil temps? I thought the Tundra didn't have a temperature sensor in the oil system, only a prediction based on engine and/or transmission operating temperatures.

 

Where is the sensor that detects engine oil temperature?

 

I understood & commented on it based on engine water temp...as I knew there is no oil temp sensor.

it was a preponderousment.

 

I'm using OBD Fusion...I monitor engine oil (now that you mention it, I'm not sure how it is calculated if there is no sensor), engine coolant, pan, and TC temps.

That's a good question...how does OBD calculate engine oil temp?

 

and, lest we forget, water evaporates at all temperatures above freezing.

 

Points awarded for the word of the day: ‘preponderousment’.

 

Right. But the way I understand it, according to Toyota, moisture doesn't effectively vaporize (boil?) out of the transmission fluid until operating temp is reached.

Or are you saying we know that trace amounts of water vaporize out of a mixture of mostly transmission fluid at all temps above freezing? Why the moisture concern from Toyota about getting it up to operating temps? Maybe it's hogwash to appease our EPA overlords. Honestly, it seems the fuel economy angle is hogwash. I have never recorded measurably better fuel economy at hotter transmission temperatures. In fact, I get better fuel economy being ultra gentle on the truck, which means on many trips, I never reach transmission operating temps.

Have we reached peak ponderosity?

 

And it seems we have a contender… perhaps the judges were hasty in their zealousfullositiousness in awarding points..

 

Yes.

It's Scientifical.

 

as it relates to evaporation....take making moonshine.

Alcohol evaps at 160degrees or therabouts - which is why you do not want your mash/pot to boil....but you can never get pure alcohol, because some % of water is vaporizing @ 160degrees.

yes, I compared transmission vaporization to distilling moonshine. I should get some type of commendation.