DexIII or DexVI?

[Maxjeep1]

I made a comment to a YouTube person that said he was having trouble with power steering noise. During his video he said he needed to add power steering fluid. I thought that might be his problem so I asked him if he put DEXIII in? He replied and said it takes DEXVI like the 4L80E transmission. He has the turbo truck and I think it’s an M1152.
Maybe I’m wrong with it not being compatible with the hydraulic/ brake system. I added DEXIII to mine after some research and asking a few questions here.

 

[Coug]

According to the newest version of the TM for ECV/REV trucks, DEXVI is used in all systems in the truck.

However:

GM put out a bulletin not long after they put out DEXVI

Bulletin clearly said only to use DEXVI in automatic transmissions.

It also clearly stated that other applications where DEXIII was used were NOT to be filled with DEXVI, and then gave alternative fluid labels (which were basically just repackaged DEXIII)


I couldn't find the bulletin, but apparently the below is from a GM owner's manual


This information applies to 2007 and prior GM passenger cars and trucks.

Dexron III is being phased out as a product name. It is being renamed Manual Transmission Fluid and carries p/n 88861800 U.S. (88861801 Canada).

If fluid p/n 88861800 U.S. (88861801 Canada) is not yet available when servicing a manual transmission or transfer case, Dexron III can be used in its place.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
Unavailability of manual transmission fluid part number 88861800 U.S. (88861801 Canada).

Recommendation/Instructio ns:
If fluid part number 88861800 U.S. (88861801 Canada) is unavailable when servicing a manual transmission or transfer case, Dexron III can be used in it's place. DO NOT use Dexron VI in place of the manual transmission fluid in any manual transmissions or transfer cases as a failure may result.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

 

[Coug]

personally, I'm running DEXIII in my power steering.

I'm not constrained like the military supply chain to minimizing the amounts of different fluids I stock for my equipment, so I see no reason to use a single fluid if there are others that are better.

 

[blutow]

personally, I'm running DEXIII in my power steering.

I'm not constrained like the military supply chain to minimizing the amounts of different fluids I stock for my equipment, so I see no reason to use a single fluid if there are others that are better.

So, Dex6 for transmission and 3 for the power steering? Dex3 for transfer case also or does it matter?

Are you able to find actual Dextron 3 ATF or using the delco stuff referenced above that has been rebranded as manual transmission fluid?

It seems that most of the ATF fluid I see available is labeled as supporting both the latest dex and merc requirements, but not sure if it's actually the best stuff to be using. Any recommendations?

https://www.amazon.com/Valvoline-Mu...=1645821722&sprefix=dextron+3+,aps,150&sr=8-5

The fluid looks new in the auction truck I recently received, but it's been sitting for 12 years so I figure it's probably a good thing to change.

 

[Maxjeep1]

I found this at O’Reillys for my power steering fluid and system.

 

[blutow]

I found this at O’Reillys for my power steering fluid and system.View attachment 859969

Thanks, I'll try to find some of that and probably just use it in everything unless there is an advantage to using the dex6 stuff in the transmission. Do you know if Dex3 is the recommended fluid for the transfer case also?

 

[Maxjeep1]

Thanks, I'll try to find some of that and probably just use it in everything unless there is an advantage to using the dex6 stuff in the transmission. Do you know if Dex3 is the recommended fluid for the transfer case also?

I don’t think it’s for the transmission of transfer case. I have not changed mine yet so I don’t know. I believe the trans/ transfer case takes the DexVI but don’t take my word for it. Maybe the 3speed trucks might take DEXIII?

 

[blutow]

I don’t think it’s for the transmission of transfer case. I have not changed mine yet so I don’t know. I believe the trans/ transfer case takes the DexVI but don’t take my word for it. Maybe the 3speed trucks might take DEXIII?

I think Dex3 was the latest greatest when many (most?) of these trucks were made, Dex6 didn't come out until 2006. I'll do some digging, a good test if I can find something in a TM that should be pretty simple.

 

[springer1981]

I've recently spent some time researching exactly these options/arguments for Dex3 vs Dex6 in both the transmission and the power steering system. I choose Dex 6 for the transmission and power steering fluid (PSF) for the steering. I suspect the viscosity of Dex 6 is what makes it a poor choice for the power steering. Here is what I've found that has swayed my decisions.

Dex 3
Viscosity is around 32
Semi Synthetic
Dex 6
Viscosity is around 29 depending on who's numbers you use
Full Synthetic
Additives for higher performance automatic transmissions

Power steering fluid vs AFT
On average power steering fluid Viscosity is 32-40
The additives in AFT promote cavitation which is not good for the power steering system in general. A quality power steering fluid helps prevent cavitation in the oil due to anti foaming additives. In performance steering systems ATF is considered a no-no. I've decided to switch to SWEPCO power steering fluid in the near future. My power steering system is running the typical power steering and hydroboost brakes. On top of that it is used for a front and rear hydraulic winch and I'm working on adding power rear steering. I'm asking a lot from the power steering system and feel the switch will be an improvement.

 

[blutow]

I've recently spent some time researching exactly these options/arguments for Dex3 vs Dex6 in both the transmission and the power steering system. I choose Dex 6 for the transmission and power steering fluid. I suspect the viscosity of Dex 6 is what makes it a pour choice for the power steering. Here is what I've found that has swayed my decisions.

Dex 3
Viscosity is around 32
Semi Synthetic
Dex 6
Viscosity is around 29 depending on who's numbers you use
Full Synthetic
Additives for higher performance automatic transmissions

Power steering fluid vs AFT
On average power steering fluid Viscosity is 32-40
The additives in AFT promote cavitation which is not good for the power steering system in general. A quality power steering fluid helps prevent cavitation in the oil due to anti foaming additives. In performance steering systems ATF is considered a no-no. I've decided to switch to SWEPCO power steering fluid in the near future. My power steering system is running the typical power steering and hydroboost brakes. On top of that it is used for a front and rear hydraulic winch and I'm working on adding power rear steering. I'm asking a lot from the power steering system and feel the switch will be an improvement.

Good info. Did you do any research on the transfer case? I'm guessing higher viscosity would be beneficial there as well.

 

[Coug]

I buy the Lucas Multi-Vehicle ATF at NAPA
Reading the tech data sheet on it, it meets DEX 1, 2 ,and 3, but not DEX 6.
Going by Viscosity, at 40C it's 38.3, so higher than the numbers springer listed above.

Also it specifically states it is recommended for use in all power steering applications with the exception of Honda.

https://lucasoil.com/pdf/TDS-Gear_Multi-Vehicle%20ATF.PDF

 

[springer1981]

Good info. Did you do any research on the transfer case? I'm guessing higher viscosity would be beneficial there as well.

Not specifically but in my recent 4L80/242 swap I chose Dex6 for the transfer case as well. The transfer case isn't affected the same as the power steering as there is no pump or high pressure line, it's basically lubrication. Dex6 should have work well in that application if we consider the heat and lubrication properties of full syn vs semi syn.

I currently have Dex3 in the power steering to be switched out for PSF. I run Dex6 in the 4L80 and 242.

 

[springer1981]

I buy the Lucas Multi-Vehicle ATF at NAPA
Reading the tech data sheet on it, it meets DEX 1, 2 ,and 3, but not DEX 6.
Going by Viscosity, at 40C it's 38.3, so higher than the numbers springer listed above.

Also it specifically states it is recommended for use in all power steering applications with the exception of Honda.

https://lucasoil.com/pdf/TDS-Gear_Multi-Vehicle%20ATF.PDF

I believe the Dex2 came in about 36-38 so that sounds about right. And I was using the 40C ratings.