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Which fluid for G56? #5450112 06/09/20 10:01 PM
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A_Harman Offline OP
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Once again, the age-old quandary of what lube to put in the G56 6-speed manual trans in the Dodge Ram diesel.

I have been running AMSoil ATF, which is what they recommend for the application. Chrysler recommends their C+4 ATF fluid. In my opinion, Chrysler really screwed the pooch by recommending ATF in the G56, when in medium duty European trucks, Mobil Trans SHC 50 DC was recommended. There was a wide gulf of viscosity between the Mobil fluid, at 15.7 cSt, and the Chrysler C+4, which was 7.5 cSt. I have read a lot of stuff on the Interweb including some lengthy and colorful threads on BITOG that showed up in Google searches. There never is a resolved outcome of any of the discussions.

Mobil Trans SHC DC is no longer available. Nor is Mobil Trans SHC. Some equivalents from other oil companies are available that claim to be replica fluids (of the SHC, not the DC version). But they're expensive.

Now we're heading into hot weather, and it's time for a fluid change. I want something with higher viscosity, but if I want to respect the Chrysler recommendation, I could find a higher viscosity ATF.

I looked on Redline's site, and they have the High Temp ATF, at 9.5 cSt. 27% higher viscosity is a significant step up from C+4. I e-mailed a question on the Contact page, and got a reply from Dave at Redline. He recommended either the MTL or MT85. MTL is 10.4 cSt. MT85 is 12.0 cSt. I have experience with MT85 on my old truck. It gave the best shifting feel of any fluid I ever ran in the NV4500.

And then there is AMSoil MTG, which I ran in the old Dodge because of the higher viscosity. It was 14.0 cSt.

So there are fluids I have mentioned above ranging in viscosity from 9.5 to 14.0 cSt. Which would you pick?


2008 Dodge Ram 3500 diesel/G56
1985 Z51 Corvette track car 355/6-speed
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel/NV4500+GV
1972 GMC 1500 shortbed project truck 307/SM465
Re: Which fluid for G56? [Re: A_Harman] #5450156 06/09/20 10:57 PM
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MolaKule Offline
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I agree with Dave at Redline and considering this a diesel I would probably use the MT85.


"So many shows out there dumb-down the country. It's so admirable to be part of a show that wants people to think." (David Krumholtz 'Charlie Epps' of NUMB3RS)
Re: Which fluid for G56? [Re: A_Harman] #5450228 06/10/20 03:55 AM
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A_Harman Offline OP
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Now that I've slept on it some, I would rather respect Mercedes' original heavy fluid recommendation. So I'm considering Redline MT85 and AMSoil MTG.


2008 Dodge Ram 3500 diesel/G56
1985 Z51 Corvette track car 355/6-speed
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel/NV4500+GV
1972 GMC 1500 shortbed project truck 307/SM465
Re: Which fluid for G56? [Re: A_Harman] #5450282 06/10/20 07:13 AM
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Langanobob Offline
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Originally Posted by A_Harman
Now that I've slept on it some, I would rather respect Mercedes' original heavy fluid recommendation. So I'm considering Redline MT85 and AMSoil MTG.


For what it’s worth, I’m running Redline MTL in the ZF6 in my 7.3L
Powerstroke. I think Ford’s recommendation is Mercon ATF. I don’t think you can go wrong with either MT85 or Amsoil MTG.

Re: Which fluid for G56? [Re: A_Harman] #5450518 06/10/20 12:51 PM
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A_Harman Offline OP
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Just picked up 5qts of MT85.


2008 Dodge Ram 3500 diesel/G56
1985 Z51 Corvette track car 355/6-speed
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel/NV4500+GV
1972 GMC 1500 shortbed project truck 307/SM465
Re: Which fluid for G56? [Re: A_Harman] #5450605 06/10/20 02:20 PM
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nascarnation Offline
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Do these transmissions have a failure mode that you're trying to protect against?
I'd think the Amsoil ATF which IIRC is a PAO based syn would easily be a lifetime fill in a manual.

Re: Which fluid for G56? [Re: nascarnation] #5450689 06/10/20 04:40 PM
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A_Harman Offline OP
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Originally Posted by nascarnation
Do these transmissions have a failure mode that you're trying to protect against?
I'd think the Amsoil ATF which IIRC is a PAO based syn would easily be a lifetime fill in a manual.


Rolling element bearings suffer from surface fatigue. I talked to another RV transporter a few months ago that said he got 350k miles out of his G56, so they do wear out. It's hard to pick out legitimate failures out of Internet discussions because so many owners have jacked the power output way past the input torque rating of the transmission. Then they break gearteeth, spall bearings, and distort the cases. I'm not going to be one of those guys. I'm keeping the engine stock for now. It has enough power for what I'm doing. My transmission has made a rushing noise at low engine rpm that goes away past 1300 rpm. I interpret this as "bearing skidding", and
believe that it can begin the process of surface fatigue. So I drive to avoid it, and am hoping that the higher viscosity can improve bearing protection.


2008 Dodge Ram 3500 diesel/G56
1985 Z51 Corvette track car 355/6-speed
2002 Camaro Z28 LS1/6-speed
2001 Dodge Ram 2500 diesel/NV4500+GV
1972 GMC 1500 shortbed project truck 307/SM465
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