Atf+4 vs Dexron vi

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Originally Posted By: Johnny2Bad
91 RAM? Are you sure Chrysler/Dodge recommends ATF+4?

+4 is basically a Mercedes-spec trans fluid and was introduced during the MB/Chrysler years around 2000 or so. My 96 RAM spec's ATF+3 in the manual, which is a substantially different lubricant.

If your rebuilder suggests Dextron 3, I'd follow his advice, although jrmason's post is interesting. You definitely don't *have to* run ATF+4 in a '91; that fluid didn't exist when your truck rolled off the assembly line. Check your manual (or download one).


ATF+3 has been discontinued for about 10 years now. ATF+4 supercedes +3 and is similar in performance characteristics except +4 retains the characteristics for at least 100,000 miles where as +3 typically was only good for 30k miles.
 
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How many pan drops am I looking at to have all the dexron III out and the new fluid in? Each pan drop I've done requires 6 quarts to fill it back up, and I believe the transmission holds 12 maybe 13 quarts total.
I'm not against running +4, I just thoutht that dexron vi was a better fluid, and I also thought dexron vi would perform closer to dex III in my transmission.
I like the way my transmission performs with dex III, the shift qaulity is great. I just want a better fluid. So I'm still leaning towords dex vi.
 
Just disconnect the line coming out of the trans cooler, stick it in a 5 gallon bucket, and have someone start the truck. You may have to put it in neutral to get the fluid circulating. As soon as the fluid starts "spitting" have your assistant shut the truck off. You can now drop the pan with out making a huge mess and you'll have evacuated about 2 gallons out of the system (give or take a quart or so.) You can loosen the valve body and let it drip over night if you want to get another quart or two out of it. Even leaving it sit over night with a catch pan under it will net a little extra. This is the only way I do a trans flush/fill. Dropping the pan only gets a fraction of the fluid out of the system and then every time you drop the pan after your draining partially new fluid.
 
Isn't it bad to run the transmission in neutral with fluid pumping out of the cooler line? I thought I've heard that can burn them up.
 
Doing the above procedure doesn't run anything dry as long as you shut the truck off when you see the flow of fluid in the cooler outpit line interrupted. That's why you need an assistant, one to watch the flow under the truck and one in the drivers seat.
 
Originally Posted By: jrmason
Doing the above procedure doesn't run anything dry as long as you shut the truck off when you see the flow of fluid in the cooler outpit line interrupted. That's why you need an assistant, one to watch the flow under the truck and one in the drivers seat.


So as soon as I start to see the fluid that's coming out of the cooler line slowing down have them turn the truck off?
And you recomend +4 over dex vi. Which one of the two fluids would provide a firmer shift? I'd have to imagine that dex vi would probly feel a little former right?
 
ATF+4 is not the correct fluid. DexronVI is the correct fluid. If you want to deviate from that, use something synthetic that meets a DexronIII or better equivalent.

There's nothing wrong with ATF+4, it's a great fluid for the electronic transmissions it was designed around, but it's simply not the correct coefficient of friction for a transmission that specifies any Dexron/Mercon fluids.
 
Yea this subject is a little hard to understand because the 727 was specd for dex II and dex III for a long time, then the A-518 came out which is a 727 with overdrive and it still specd dexron from 1989 to 1993, then in 1994 or 1995 chrysler changed the A-518 to the 46re, basically same transmission but much more electronically controlled and that's when they changed the spec to +3 and +4.
I'm going to go ahead and try the dex vi and see how it performs and feels in my transmission. Still not sure if I want to try pumping it in nuetral with a cooler line disconnected. A couple pan drops would do the same thing, specially if I got a pan with a drain plug.
 
The only reason your truck was ever specd for DEX is because Chrysler didn't make their own ATF at the time that was suitable for torquflite transmissions. Around 93/94 when ATF+3 was released it was deemed backward compatible to DEXIII, and highly recommended. DEXIII is an ancient fluid with horrible shear properties. I dont know that you'll notice a difference in shift quality with DEXVI but DEXVI is a thinner viscosity fluid compared to DEXIII and ATF+4 (see my first post). For that matter, DEXVI is the thinnest fluid on the market out of all the OEMs. While your transmission is probably fine to run just about anything, I'd be more inclined to stay close to the viscosity of the OEM specd fluid. DEXVI is not close (see above post).

As for evacuating the ATF out the cooler line, many shops have been doing this for years. Its an old trick to get as much of the fluid out of the system as possible. Doing pan drops when you need to exchange all the fluid is wasteful, time consuming, and inconsistent. Not bad when doing PM work but not the best practice at all when all the fluid needs exchanged.
 
Originally Posted By: jrmason
Many torqueflite builders (A727, A518, A618, etc) used to tell you to run the cheaper Dex III fluid because it is a "stickier" fluid which grabs the clutches differently than a full synth like ATF+4 will. The downside to this is, the DEX will wear out quicker and lose visc much faster than ATF+4. In the 20 hour KRL shear test, DEX III suffered a 40% viscosity loss compared to ATF+4. The builder of my 47RE initially recommended DEX for my trans when he built it for the above reason and price but those were the only reasons for his recommendation. ATF+4 is a superior fluid in every way to DEXIII. Ive been using ATF+4 @30k mile intervals for the past 100k miles and my trans has very little clutch wear when I drop the pan and the bands need minimal adjustments. ATF+4 is technically a 100k mile fluid but I change mine out more frequently due to my modified engine and the fact that it gets used to tow heavy loads.

As for using Dex VI its interesting to note the difference in viscosity. Viscosity plays an important role in TC performance and its stall characteristics.

ATF+4 cST@40C 33.24 cST@100C 7.51
DEXIII cST@40C 34.70 cST@100C 7.70
DEXVI cST@40C 29.50 cST@100C 5.83

The way I see it, you've got two valid options as you mentioned. Either DEXVI or ATF+4. DEXIII would be out of the picture if it were my transmission. ATF+4 is friction modified for the electronic control programs TCM. ATF+4 lets the TCC operate in patial lock up mode which other fluids are not capable of without slippage or shudder. None of this applies to you, however I feel ATF+4 with its group III base and patented shear stable VI improver make it a superior fluid. Just my opinion.


Just a couple of comments,

1. Shear stability - 40h KRL - % viscosity loss:

ATF +4 20.2
DEXRON III 40.1
DEXRON VI 6.3

So in terms of retaining viscosity DEXRON VI is better than either of them.

2. In partial lock-up mode the TCC is supposed to slip, that's the point of it, it's just not supposed to shudder!
 
Originally Posted By: jrmason
...DEXVI is the thinnest fluid on the market out of all the OEMs. While your transmission is probably fine to run just about anything, I'd be more inclined to stay close to the viscosity of the OEM specd fluid. DEXVI is not close (see above post)....


How about the Ford LV fluids?

Unless the transmission has excessively worn internals (loosey-goosey), I don't see how a 16% drop in viscosity is going to matter.
 
It shouldn't be a loose transmission, it was just re-built 5000 Miles ago.
So it's a 16 percent difference in viscosity between +4 and dex vi or between dex III and dex vi?
 
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Originally Posted By: pjc360
It shouldn't be a loose transmission, it was just re-built 5000 Miles ago.



Oh, good, I apologize for missing that info earlier.

Originally Posted By: pjc360
So it's a 16 percent difference in viscosity between +4 and dex vi or between dex III and dex vi?


Both.

DexronVI is 16% lower in viscosity than ATF+4@100C.

DexronVI is 16% lower in viscosity than DexronIII@100C.


ATF+4 and DexronIII/Mercon have the same viscosity@100C, about 7.3 cSt.

DexronVI has a Kinematic Viscosity@100C between 5.9 and 6.1 cSt.

MaxLife Dex/Merc ATF has a Kinematic Viscosity@100C of 5.9 cSt.

DexronVI has a Kinematic Viscosity@40C of 29 cSt.

ATF+4 has a Kinematic Viscosity@40C of 34 cSt.

Dex/Merc has a Kinematic Viscosity@40C of 35 cSt.

Valvoline MaxLife Dex/Merc has a Kinematic Viscosity@40C of 29 cSt.

So you see, there is not a whole lot of viscosity differences, only about 1 cSt.

I would recommend either a licensed DexronVI or Valvoline MaxLife Dex/Merc.
 
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I think I'm set on dex vi for now, my local Napa is having a sale on valvoline atf's right now, I can get valvoline dex vi for 5.99 a quart. I will try disconnecting the return cooler line and running the transmission in nuetral to drain the dex III out of it. Hopefully doing it that way gets most of the dex III out.
 
Originally Posted By: MolaKule
Originally Posted By: jrmason
...DEXVI is the thinnest fluid on the market out of all the OEMs. While your transmission is probably fine to run just about anything, I'd be more inclined to stay close to the viscosity of the OEM specd fluid. DEXVI is not close (see above post)....


How about the Ford LV fluids?

Unless the transmission has excessively worn internals (loosey-goosey), I don't see how a 16% drop in viscosity is going to matter.



Agreed.

And I'll add this ...

While VI and LV both are "thinner" out of the bottle, they both probably retain their vis better than the old DEX/Merc fluids, which shear quickly. I've got a lot of UOAs for the old Dex III(h) that show it drops down to the low 5's in a hurry; well below where you'll see VI or LV settle to.

As with engine oil, the vis range is important, but not something to marry oneself to as if it were the ONLY thing to worry about.

Concern yourself with how it performs and protects, not what it seems to be in the bottle.
 
4.2 cst? That's pretty thin. How many miles does it take to make dex III shear that much? I only have about 5000 miles on th dex III that's in my transmission.
 
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