Synthetic vs. Dino Diff Fluid Change - 04 Chrysler

[shadowvox6]

Group,
I have read (and heard) that the diff's in our cars require Dino Diff Fluid due to the seals in the diff are not compatible with synthetic fluid. I ran synthetic diff fluid in the 99 forever with no issues. When I got the 04, I originally put synthetic (Mobil 1) 75W90 in it. I changed it out later to put Valvoline 80W90 (Dino) in it. I keep waffling back and forth over this.

In the owner's manual it clearly states this:

Quote:

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Axle Differential (front-rear): Mopar Hypoid Gear Lubricant (SAE 80W90). Do not use synthetic gear lubricant.

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Any thoughts?

 

[unDummy]

There is an issue with certain RTV's and gear oil. There is a thread here concerning many that have leaks caused by gear oil dissolving the RTV.

What vehicle? What type of gasket material?

If you have no leaks with the synth, then use it. If you are forced to reseal your diff, then you should stick with the mineral gear oil.

I would also hope that better properly applied RTVs and the anaerobric ones don't have this issue.

 

[mikeg5]

RTV's??? never heard of the syn making things leak ---- in the diffs

 

[MaximaGuy]

Amazing in this world of synthetics a manufacturer would take short cuts in sticking in a seal that isn't compatible with syn. This isn't some vehicle manufactured in 1970's it is pretty new for a 2004 vehicle.

On top of Chrysler is offering a lifetime warranty on their drivetrain, curious what cavet's come with that freebee (I guess owners need to memeorize their user's manual in and out).

 

[shadowvox6]

Quote:

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There is an issue with certain RTV's and gear oil. There is a thread here concerning many that have leaks caused by gear oil dissolving the RTV.

What vehicle? What type of gasket material?

If you have no leaks with the synth, then use it. If you are forced to reseal your diff, then you should stick with the mineral gear oil.

I would also hope that better properly applied RTVs and the anaerobric ones don't have this issue.

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This is on a 2004 Chrysler 300M Special.
42LE Transaxle

My guess is that it is an RTV sealant (seeing how Chrysler uses it in most gaskets)

 

[Arved]

Quote:

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My guess is that it is an RTV sealant (seeing how Chrysler uses it in most gaskets)

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Is the chain lubricated by ATF, or by the gear oil? I think it's ATF. The chain cavity has a baffle fastened by RTV, and the chain cover itself uses RTV as a sealant. The only other use of RTV in the 42LE Transaxle is the the pan, but as you know, there's a TSB to use a metal sandwich gasket for that, and that's an ATF(+4) wetted area anyway.

The TSB for the pan gasket mentions a problem with uncured RTV causing foaming when it contacts the ATF+4, and the ATF+4 is a synthetic (Group III base oil), so as long as the RTV is cured, the implication is the RTV is safe when it comes into contact with Synthetic lubricants.

FWIW, the FSM specifies "Mopar(TM) Fuel Saving 75W-90 Petroleum-Based Hypoid Gear Lube." While there may be an admonition against synthetic oil in your owners manual, there's no such admonition in the FSM. Last time I checked, "synthetic" oils are still petroleum oils, if you accept the definition of petroleum being hydrocarbon compounds. Now, if you insist on petroleum refering to hydrocarbon materials originating from beneath the ground then that's another matter, but a hydrocarbon doesn't know if it came from the ground or was synthesized in a factory, and certainly doesn't behave any differently.

Note the specification in the owners manual is different from the FSM. Owners manual states "Mopar Hypoid Gear Lubricant (SAE 80W90). Notice the slight difference in viscosity, and the lack of a "Fuel Saving" labeling.

The only seals that are wetted by the gear oil are the output shaft seals (2), and one of the transfer shaft seals (there's two transfer shaft seals, one oil wetted, the other ATF wetted, and a dry space in between with a weep hole for leak detection). Unfortunately, I have no idea what material is used for these seals, or how they may be effected by Synthetic (vs. conventional) oil.

I don't mean to be arguementative - only trying to help. We've both got the same cars, and the same concerns here.