Just as a note, that's the same as drain/refill, when using the same amount of oil. Old fluid will mix with the new one in torque converter, drain pan...
This is not toothpaste to be pushed out unmixed.
Lexus Toyota "Lifetime ATF" - baloney
- Thread starter JeffKeryk
- Start date
This is not toothpaste to be pushed out unmixed.
I bought a Lexus GX460 last February with 72k miles. When i got it home one of the first things i had done was the trans fluid.
About 4000 miles later I used it to tow my travel trailer and, in typical Toyota fashion, my fluid hit 245*F multiple times in fairly cool weather. Shortly after that trip I did a bunch of drain and fills with Valvoline MaxLife and the fluid that came out was extremely dark with only 5k miles on it.
The 2019+ Tundras have a really poor transmission cooler setup and TFLTruck saw temps in the 240’s on a fairly cool day as well.
So yeah, if you tow or do anything rugged with your Toyota, change the fluid.
About 4000 miles later I used it to tow my travel trailer and, in typical Toyota fashion, my fluid hit 245*F multiple times in fairly cool weather. Shortly after that trip I did a bunch of drain and fills with Valvoline MaxLife and the fluid that came out was extremely dark with only 5k miles on it.
The 2019+ Tundras have a really poor transmission cooler setup and TFLTruck saw temps in the 240’s on a fairly cool day as well.
So yeah, if you tow or do anything rugged with your Toyota, change the fluid.
IMO every Toyota used for towing needs to have an auxiliary cooler installed. Their transmission coolers are not adequate for towing.
I base this by my own transmission temperature measurements on a few models. Temps over 200 degree F, for sustained periods, are crazy in my book.
Using synthetic is just "fixing" the oil varnishes problem (maybe), but the seals are still baked at over 250+ degree F.
Yes, but when you run 14 quarts through, there‘s not much of that original fluid left.
What comes out at the end is cherry red - looks like new fluid.
Similar to when you change your engine oil, there will be a small amount of the old oil that you can’t get out.
I don’t think the small leftover amount has much effect in either case. In both cases, for all intents and purposes, you have replaced the system’s fluid.
Is it better than doing a ”spill & fill” at more frequent intervals? I don’t know. I guess you’d have to do a controlled test to get the answer to that question. Some guys here prefer that method, especially those who do a lot of towing and hauling. Perhaps on some failure-prone transmissions, doing both might be a good idea.
Personally, I prefer to swap the entire system capacity at less frequent intervals, on my truck, especially since I don’t do heavy towing and hauling (couple of motorcycles or a U-Haul from time to time), and it mostly serves as my commuter on my 36-mile highway round trip commute 4-5 days per week.
And I changed diff fluid at the same time.
You can do exactly the same with successive drain/refills (with drives in between) in amount of 14 Qt.
None is "better" or "worse" IMO.
MolaKule
Staff member
The newer formula LV's and ULV's not only incorporate higher percentages of higher Group fluids, but also have improved and more stable DI and VII components which means higher shear stability, more stable Friction Modifiers, improved Anti-Oxidation, and better Metal Inhibitor and Anti-Wear chemistry.
The viscosity reduction from 7.5 cSt to 5.9 and 4.5 cSt's gives a fractional increase in fleet fuel efficiency. While the viscosity was decreased, the chemistry was much improved and gets incrementally improved with each new ratchet down in viscosity.
The LV and ULV ATF's, while they have a lower starting viscosity, will remain in grade at much higher temperatures.
And their low temperatures properties are superior as well with Brookfield viscosities well below 12,000 cp.
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MolaKule
Staff member
Some prefer to incrementally do drain and refills to slowly clean neglected transmissions, that is, those with high mileage on the fluids.
Transmission specialists will prefer to do a complete fluid exchange in order to remove ALL of the oxidized fluid, including fluid in the torque converter, and which also removes most of the particulates (clutch and metal buildup) that have accumulated.
Wouldn't be better to start at the SAME viscosity, as specified by manufacturer, and remain in grade? I know that, for example, AMSOIL has a normal viscosity synthetic ATF.
I prefer to save money in transmissions than on a fractional gas mileage improvement.
MolaKule
Staff member
The Dexron VI series use the improved chemistry, as well as the Amsoil ATF and the fuel efficient LV ATF (ATL), as do the Redline series of fluids.
If you are concerned that a fractional decrease in viscosity results in increased internal wear, then your concerns are misplaced.
Fractional being 21%.
So... possible reduced pressure on internal clutches/bands is no biggie? Because we have a strong fluid that protects the metallic gears?
My post was about people using LV in transmissions that were not designed for that.
Viscosity is very important in a transmission that works using that viscosity to create pressure differentials inside the valve body.
MolaKule
Staff member
It seems you have changed the cause-and-effect discussion to a different topic.
When Dexron VI was introduced GM stated it could be used in any of their Automatic Transmissions, that is, it was back-speced, so apparently GM drivetrain engineers had tested Dexron VI in the older, loosey-goosey transmissions of yore and found no pressure problems with its use.
Exercise for you: Take a Dexron III-H of 7.5 cSt@100C, at an AT internal pressure of 150 psi, and recalculate for the resulting pressure for an ATF of 5.5 cSt@100C. All temps are at 100C. What is your answer?
Who makes that pressure? Let me tell you - the resistance to fluid flow. If there is no resistance, the displacement pump makes zero pressure.
The same way, an open water hose has no static pressure inside either. Only when flow is restricted (friction pressure drop in a valve) you get some static pressure inside that fluid.
So yes, friction is super important in how a hydraulic circuit maintains the pressure.
It's fluid dynamics 101, some dude, Bernoulli figured it out a while back.
MolaKule
Staff member
Anyone who has investigated AT hydraulic systems knows it is the pump that creates hydraulic pressure, but that is not the question. The question was/is: If a lower viscosity fluid of the same volume is placed inside the AT, what will be the pressure change within the original transmission in question?
I'll give you the answer since you seem not to be able to determine it.
The pressure change will be essentially zero and the pressure measured at the same point would be 150 psi. Using ratios and proportions would yield an answer of 108 psi but that would not be correct, because...
Transmission Hydraulics: Main PR Valve Line-Ups | Sonnax
Hydraulics are critical for transmissions, and one of the most significant components is the main (primary) pressure regulator valve. Read more today!
or
Hydraulics Fundamentals: Main pressure regulator valve lineups - Transmission Digest
Forces, pressures and flow rates are critical considerations in all stages of a transmission’s lifecycle.
www.transmissiondigest.com
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Amsoil blue cap SS in my 15 Tacoma. I also use it in my wife’s 19 Honda Pilot that uses DW1.
I suspect those charts may be old data. The trans in my truck is regulated to 205F nominal, with a life expectancy of under 50k per the chart. Thats either alarmist or old data. Ive had a couple of town and countries with an instrumented trans.... those guys start at 160F and spent plenty of time 180-220F, and alarmingly more on a hot hill climb with the AC on... 240+.... those were undercooled! They were not considered robust units, but both my vans were high miles, one did some towing, and they certainly made it farther than the chart suggests. My tundra (2006) towed heavy all day long between 160-180F, again, with a 3rd party gauge on the cooler line. With the AC off on a daily basis it might reach 130, never went over 160. I know the new ones run warmer by design.
Some OTR professional drivers will pay more attention to diff temps. Those get hot and are not actively cooled. Ive experienced similar when towing on grades with a heavy trailer.... trans at 205 and heat just pulsing off the diff, and grease leaking out of sealed axle bearings. that was an eye opener. The weak spot was not the trans...
Some OTR professional drivers will pay more attention to diff temps. Those get hot and are not actively cooled. Ive experienced similar when towing on grades with a heavy trailer.... trans at 205 and heat just pulsing off the diff, and grease leaking out of sealed axle bearings. that was an eye opener. The weak spot was not the trans...
Not saying this is right or wrong, but for as long as I can remember, my Dad has had both a car, and one ton diesel 4x4 to. About every 10,000 to 15,000 kms he drops the transmission pan, new filter, puts the pan back on, and refilled with new ATF. Not sure what percentage of the oil actually drains out, as only some of it does. His theory is that doing it often, will after some time ensure that most of it gets replaced with new fluid, before it gets too old. He has never had a transmission problem, and he works his trucks hard.
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I mean, I never went to that extreme but I once owned a Honda Accord with the old “trouble transmission” and I changed the fluid once a year. It averaged out to be 15,000-25,000 miles, depending on how much I drove that year. You couldn’t drop the pan on those, so they were just simple drain and fills. Never had a problem with that transmission as long as I owned it (289,000 miles). And those cars/transmissions were known to fail between 70,000-120,000 miles. Class action suite. Black eye for Honda.
Not one one single problem in 289,000 miles...wait. I did have to replace a transmission switch at 285,000 miles, but it was a two minute fix and cost me like $35 bucks.
Run a pump with an open hose, no restriction. What pressure do you have on that open hose?
Any mechanical engineer knows that pumps only moves fluid, creates flow, creates kinetic energy, but the actual head (static pressure) is from the external circuit and associated fluid friction.
Even your links show valves as pressure regulators - valves are restrictions, with local pressure drop that is proportional with fluid viscosity.
Those regulators were calibrated for a certain viscosity fluid. Slippery fluid can create a lower pressure on those regulators.
Also internal orifices (valve body) are calibrated for fluid viscosity, not for static pressure.
In extremis, imagine you run water or air at 150 psi trough that transmission. Will it work? What's different? Viscosity!
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MolaKule
Staff member
What's a slippery fluid?
You still haven't answered any of the questions and now you bring up internal orifices?
The dimensions of internal orifices in the valve body are designed for considerations with respect to mass flow rate and differential fluid pressures, basic Bernoulli physics.
Spring rates and solenoid pulsing in the pressure regulators determine line pressures.
I highly suggest you study the basic equations of viscous fluid flow through ducts, pipes, and orifices and the effect of wall friction on viscous viscous fluid flow through ducts, pipes, and orifices in order to get a basic understanding of fluid flow and how hydraulic systems function in an AT.
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MolaKule
Staff member
Those charts are obsolete because they assume first generation-type Dex/Merc fluids and do not consider fluids with the later, enhanced additive and base oil chemistry.
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