Dexron VI fuel efficiency?

[TexAndy]

So I was reading up on Dexron VI, and saw this claim

Dexron VI is of a slightly lower viscosity when new compared to the prior Dexron fluids (a maximum of 6.4 cSt at 100°C for Dexron VI and 7.5 cSt for Dexron III), but the allowed viscosity loss from shearing of the ATF during use is lower for Dexron VI, resulting in the same lowest allowed final viscosity for both Dexron III and VI (5.5 cSt).[SUP][5][/SUP] The lower viscosity is intended to gain improvements in fuel economy by lessening parasitic drag in the transmission.

I'm curious to know if this would amount to a noticeable, real world improvement in the fuel efficiency of a 1009.

I could do a quasi-scientific test, except I don't know for sure what's already in my cucv. Got it from GSA auction in San Antonio last year, so it probably has whatever the military put in it.

Also, if I do change the transmission fluid and filter and see a real improvement in fuel economy, it won't really indicate a conclusive result, as I'll have more than one variable at play (fresh ATF/filter AND updated ATF formula)

Has anyone else tried this? What was your result?

 

[98G]

I strongly suspect the difference is well to the right of the decimal point. Far enough to get lost in random variations...

 

[quickfarms]

I strongly suspect the difference is well to the right of the decimal point. Far enough to get lost in random variations...

Spoken like a real world engineer who has been out of school for a few years.

 

[TexAndy]

I suspect you're right.

I was planning to change the fluid anyways since it's still running on the same ATF it had when I got it.

 

[rustystud]

The new Dexron VI is basically for the hybrid transmissions. We use it on our bus hybrids. It is a synthetic blend and not worth the amount of money they are asking for it. It really won't help your TH400 work better and in fact could actually be too slippery for proper clutch engagement.

 

[TexAndy]

The new Dexron VI is basically for the hybrid transmissions. We use it on our bus hybrids. It is a synthetic blend and not worth the amount of money they are asking for it. It really won't help your TH400 work better and in fact could actually be too slippery for proper clutch engagement.

I haven't seen any claims of Dexron VI being any more slippery than Dexron III. Only of having a lower initial viscosity at a given temperature.


And the geared clutch disk thingies are swimming in ATF in normal operation, anyways, aren't they? How much more slippery could one ATF be over another, especially when the newer one is advertised by GM to be backwards compatible with older GM transmissions?

For the sake of argument though... where can I find actual Dexron III for sale? Is it even still made?

I see plenty of things which claim to meet Dexron III transmission requirements, none of which are actually Dexron III.

 

[cucvrus]

I have been using the Dexron VI for the past couple years. I purchased 4 - 5 gallon buckets at a sale I was at when a local dealership closed up. No issues that I am aware of. And I bought some surplus Dexron VI that was out dated.

 

[the skull]

You're talking about fuel mileage with 30 year old
extreme duty equipment. I'm getting 11-14 mpg with
my M1008, depending on the load, trailer, etc. My diesel
guy has a newer 7.3 Ford and gets 9-10 no matter what.
I hope he doesn't sabotage my injector pump when he
rebuilds it.

 

[rustystud]

I haven't seen any claims of Dexron VI being any more slippery than Dexron III. Only of having a lower initial viscosity at a given temperature.


And the geared clutch disk thingies are swimming in ATF in normal operation, anyways, aren't they? How much more slippery could one ATF be over another, especially when the newer one is advertised by GM to be backwards compatible with older GM transmissions?

For the sake of argument though... where can I find actual Dexron III for sale? Is it even still made?

I see plenty of things which claim to meet Dexron III transmission requirements, none of which are actually Dexron III.

When I used to build racing transmissions we always used Ford transmission fluid. It had a higher coefficient of friction allowing the clutches to grab harder. Dexron always has had a slippery formulation and now it is even more slippery. You need to have the clutches be able to grab to prevent slippage. Slippage causes burning of clutches. In the newer transmissions this is accomplished with higher clutch pressures and tighter clearances between clutch packs. The older designed TH400 has an average of .60" clearance in it's clutches. Also the return springs are not as strong as the newer designs. As far as buying Dexron III , I've seen it at 'O' Reilys Auto.

 

[MarcusOReallyus]

Years ago I read an article in a car magazine. They dediced to see what kind of MPG gains they could get by using synthetics. I don't recall the car - it was a sedan. They changed out ALL the lubes in the vehicle; engine oil, trans fluid, differential, wheel bearing grease, whatever. If a synthetic was available, they used it. All Royal Purple products, BTW. I seem to recall they were checking up on RP's claims.

They gained 4 mpg, which is nothing to sneeze at, but they had to do ALL the fluids to get that.


BTW, Rusty, I just checked O'Reilly's site. Couldn't find any Dex III. Lots of Dex III/Merc replacements, but read the label - it's not really Dex III. It will usually say something like, "Suitable for use in transmissions requiring Dexron III or Mercon fluid."

 

[rustystud]

Years ago I read an article in a car magazine. They dediced to see what kind of MPG gains they could get by using synthetics. I don't recall the car - it was a sedan. They changed out ALL the lubes in the vehicle; engine oil, trans fluid, differential, wheel bearing grease, whatever. If a synthetic was available, they used it. All Royal Purple products, BTW. I seem to recall they were checking up on RP's claims.

They gained 4 mpg, which is nothing to sneeze at, but they had to do ALL the fluids to get that.


BTW, Rusty, I just checked O'Reilly's site. Couldn't find any Dex III. Lots of Dex III/Merc replacements, but read the label - it's not really Dex III. It will usually say something like, "Suitable for use in transmissions requiring Dexron III or Mercon fluid."

Don't get me wrong about "Synthetic fluids" . I have replaced all my differentials ( and manual transmissions) to synthetic gear oil and all wheel bearings to synthetic grease. I'm also running a Synthetic transmission fluid similar to Royal Purple. I also run Mobil 1 synthetic motor oil (except in the deuce I use Rotello synthetic). It's that I use a transmission oil rated to Dexron III not the lower viscosity Dexron VI,
since my 1984 Chevy 1 Ton has a TH400 transmission. If I was running a newer 6L80E or even one of the newest 8L90E transmissions I would use the Dexron VI .

 

[TexAndy]

What does the viscosity have to do with it? We're talking about parts that are literally submerged and fully surrounded by this fluid, aren't we? I could see viscosity being an issue on something like back gears on a lathe, where centrifugal force would fling it off the gear. But in this case, the part to be lubricated is literally submerged in the lubricant.

 

[frank8003]

What does the viscosity have to do with it?

Viscosity is everything.
All that has been built needs to run in whatever the engineers built it for. The specifications are the ultimate at the time specified.
Then again, What do I know, I just burn the stuff.
Automatic transmission fluid (ATF) is a special lubricant used in automatic gearboxes, hydraulic-power-assisted steering systems and in the transfer cases of 4WD systems of cars and trucks.

http://www.viscopedia.com/viscosity-tables/substances/automatic-transmission-fluid-atf/

and from http://www.zr2usa.com/mboard/index.php?showtopic=13922


Normal transmission operation makes internal clutches and non magnetic metal bushings wear and shed tiny amounts of worn material into the trans fluid. This gritty stuff flows around with the fluid everywhere the fluid is pumped. Detergents in the trans fluid keep the grit dissolved so it doesn't settle or solidify in valves, passages and seals. The trans fluid can only do this for so long before the detergents start to break down due to to prolonged heat. Given long enough the amount of grit will be so much that it starts to build up, clogging valves, passages and worse yet creating friction in bearings and surfaces that need clean lubrication.

 

[joshuak]

What does the viscosity have to do with it?

Good question, I'd like to share some of my findings.

"For effective lubrication the viscosity must conform to the speed, load and temperature conditions of the lubricated parts." Info. obtained here.

"The viscosity will determine how easily the oil is pumped to the working components, how easily it will pass through the filter, and how quickly it will drain back to the engine. The lower the viscosity the easier all this will happen. That is why cold starts are so critical to an engine because the oil is cold, and so relatively thick. But, the lower the viscosity, the less the load the oil can support at the bearing on the crankshaft. The higher the viscosity, the better the load it can support. Even this, however, has a trade-off, since the higher the viscosity, the more the drag at the bearing, and hence, potential power loss, or increased fuel consumption. So a compromise is chosen to minimize power loss, but maximize load support.
For domestic use, engine life is important, and in the main you should adhere to the recommended viscosity for your engine. For motorsport, engine life is not critical, winning is, so these high performance engines can use lower viscosity oils to maximize power output to the wheels, but then again they generate a lot more heat so may use a higher viscosity anyway." Info. obtained from here (good read I thought).

Mr. Frank, you beat me to the draw, I'll leave it up for more info. though or please delete mods, if unnecessary.

 

[TexAndy]

Viscosity is everything.
All that has been built needs to run in whatever the engineers built it for. The specifications are the ultimate at the time specified.
Then again, What do I know, I just burn the stuff.
Automatic transmission fluid (ATF) is a special lubricant used in automatic gearboxes, hydraulic-power-assisted steering systems and in the transfer cases of 4WD systems of cars and trucks.

http://www.viscopedia.com/viscosity-tables/substances/automatic-transmission-fluid-atf/

and from http://www.zr2usa.com/mboard/index.php?showtopic=13922


Normal transmission operation makes internal clutches and non magnetic metal bushings wear and shed tiny amounts of worn material into the trans fluid. This gritty stuff flows around with the fluid everywhere the fluid is pumped. Detergents in the trans fluid keep the grit dissolved so it doesn't settle or solidify in valves, passages and seals. The trans fluid can only do this for so long before the detergents start to break down due to to prolonged heat. Given long enough the amount of grit will be so much that it starts to build up, clogging valves, passages and worse yet creating friction in bearings and surfaces that need clean lubrication.

What does the viscosity have to do with it, given that the Dex VI has lower initial viscosity at given X temp, but the exact same minimum permissible viscosity?

If we're going just by "run it in what the engineers built it for" then Dexron VI is perfectly acceptable for use in the TH400. Because the engineers who developed it have stated exactly that. Run Dex VI in all previous GM-designed transmissions which called for Dexron II or III ATF. Which is what I plan on doing.

I was, however, trying to elicit further discussion from the person who said he didn't run Dex VI in the TH400 due to viscosity and or lubricity differences. I didn't want to put words in his mouth, but it seemed like he was equating lubricity with viscosity.

 

[TexAndy]

Good question, I'd like to share some of my findings.

"For effective lubrication the viscosity must conform to the speed, load and temperature conditions of the lubricated parts." Info. obtained here.

"The viscosity will determine how easily the oil is pumped to the working components, how easily it will pass through the filter, and how quickly it will drain back to the engine. The lower the viscosity the easier all this will happen. That is why cold starts are so critical to an engine because the oil is cold, and so relatively thick. But, the lower the viscosity, the less the load the oil can support at the bearing on the crankshaft. The higher the viscosity, the better the load it can support. Even this, however, has a trade-off, since the higher the viscosity, the more the drag at the bearing, and hence, potential power loss, or increased fuel consumption. So a compromise is chosen to minimize power loss, but maximize load support.
For domestic use, engine life is important, and in the main you should adhere to the recommended viscosity for your engine. For motorsport, engine life is not critical, winning is, so these high performance engines can use lower viscosity oils to maximize power output to the wheels, but then again they generate a lot more heat so may use a higher viscosity anyway." Info. obtained from here (good read I thought).

Mr. Frank, you beat me to the draw, I'll leave it up for more info. though or please delete mods, if unnecessary.

I'm not an expert, but I don't think it is recommended best practice to put ATF in an engine, anyways. Regardless of viscosity. Though it probably wouldn't hurt too much.

 

[Recovry4x4]

Viscosity for Dummies. Water has a higher viscosity than air. Kick your leg out in front of you as fast as you can now go get in the pool and do the same. Which area offered the fastest leg movement?

 

[TexAndy]

Viscosity for Dummies. Water has a higher viscosity than air. Kick your leg out in front of you as fast as you can now go get in the pool and do the same. Which area offered the fastest leg movement?

The reason you can move your limbs in air faster than you can water is because of fluid density. Not viscosity.

Water is a denser fluid than air.

Density and viscosity are not the same thing.

 

[Recovry4x4]

The reason you can move your limbs in air faster than you can water is because of fluid density. Not viscosity.

Water is a denser fluid than air.

Density and viscosity are not the same thing.

I agree but it greatly simplifies the common effect. Perhaps a better example would be to kick your leg in WD40 vs gear oil.

 

[cbear]

You can not buy new official Dex III, because GM no longer sells the license, the patent is expired, hence Dex VI. Dex/merc will be the closest to original.