Synthetic vs Dino in diffs: myth or not

[Kira]

WILDCARD: When I replaced the gear oil in my 16 year old truck I used conventional because I didn't want a new, aggressive synthetic eating the old seals away.
In other words, I applied the old, "synthetics cause oil leaks" theory to my diffs.

Hey man, Street Tribology.

 

[RDY4WAR]

Nvmd

 

[RDY4WAR]

Shouldn’t you then exercise your authority and ban me?
You must be the BITOG SECURITY POLICE!
…typed with fearful trembling hands….

When 250+ vehicles are purchased annually from a manufacturer that met bid specifications, one should adhere to specific service intervals and recommendations by that manufacturer.
That’s called developing a partnership for generous considerations related to warranty and non-warranty repairs to save taxpayers’ dollars and reduce downtime for a law enforcement-public service fleet.
I really would have been fired if that partnership would have been severed.

Don’t think it matters what a self proclaimed keyboard security policeman on BITOG thinks…

Just folks talking about their automotive stuff is all this is…

Get in touch with reality please.

Nowhere in their warranty statement does it mention the oil. To be sure though, I messaged them asking for an engineer to (once again) answer this question for us. Hopefully I'll get a response rather soon.

This is the only thing their warranty statement states about exemptions.

This warranty does not apply to products that have been modified, improperly applied or installed on vehicles used for commercial or racing purposes.

Therefore, I don't see them denying a claim because someone used synthetic gear oil since it is not specifically stated. In fact, I'd say more than half of customers violate that warranty day 1 by taking their new Eaton diff to the track and beating on it.

Warranty statement: https://www.eaton.com/content/dam/e...on-control/eaton-differential-warranty-en.pdf

In reference to "why are you here," I will regress on that comment as it was a bit much. I apologize for that. In no way did I intend for that to be taken as "get out" or anything of that sort. You have a different view on things here, and we will likely not see eye to eye, and that's okay.

 

[PontiacHO]

I hear you and thanks. Let’s keep this discussion going. I am learning from you and others.
Likewise my snarky comments were uncalled for.
I enjoy sharing our experiences and differences.
That’s why I’m here.
We are blessed to have the opportunity to have this freedom.
I’m asking you…
Why does Eaton recommend standard dino?
My guess is they fear that someone will use something that sets up clutch chatter in their diff…?

 

[wpod]

My neighbor bought a used Haybine 4 years ago and it is a 1970s model in pretty good shape, there was a few things wrong with it and we have been repairing / rebuilding it as needed and it now works great . When he first bought it one one the two gear boxes would get really hot to where you couldn't put your hand on it and the oil boiled or foamed out. The oil was a greenish new looking sticky gear lube. We decided to change the oil and look for metal in the drain pan. we drained the oil and it looked fairly new and there was no metal. We put M1 syn oil in the gear box and made some hay and the gear box barely got warm. Was it the syn oil reducing the friction or the sticky gear lube causing the heat?

 

[SwampSurvivor]

I run the cheapest gear oil possible in my Cherokee. It has 4.88s and a torqmasters locker in the front. I do water crossings a lot so I have to change the oil frequently.

 

[RDY4WAR]

I hear you and thanks. Let’s keep this discussion going. I am learning from you and others.
Likewise my snarky comments were uncalled for.
I enjoy sharing our experiences and differences.
That’s why I’m here.
We are blessed to have the opportunity to have this freedom.
I’m asking you…
Why does Eaton recommend standard dino?
My guess is they fear that someone will use something that sets up clutch chatter in their diff…?

All good. Thanks for understanding.

I've spoken to Eaton twice about this. The first time, they told me it was due to the lower friction coefficient of synthetic oil causing issues with the helical gear LSDs. The second time I was told "synthetic is too thin" which is just ridiculous and made me not want to buy from them again.

The first one I disagree with since the friction coefficient between group II conventional and group III and IV synthetic is not that much different. In a sliding couple with borided surface vs rotation speed, the difference between conventional and synthetic is ~0.010 (0.165 vs 0.155) after ~8 minutes at 20 Mpa load.

See white paper titled "Experimental Analysis of Tribological Processes in Friction Pairs with Laser Borided Elements Lubricated with Engine Oils" published in December 2020. https://www.mdpi.com/1996-1944/13/24/5810/pdf

The second reason they gave is just asinine. It takes 30 seconds to google and disprove that one. A 90 grade gear oil is a 90 grade gear oil viscosity regardless of the base oil.

Where the issues with the helical gear LSDs would show in elastohydrodynamic lubrication down to boundary lubrication which is where the additives play much more of a role than the base oil. What they likely don't want people doing is buying something like Mobil 1 LS 75W-90, which contains a friction modifier additive package, that will alter the dynamic friction of the gears under load. They don't want people using the FM, not the base oil. There are synthetic base oils that don't contain a FM pack. Red Line 75W-90 NS and Amsoil Severe Gear 75W-90 are good examples of synthetic gear oils that do not contain (or contain very little) that FM pack.

 

[RDY4WAR]

I run the cheapest gear oil possible in my Cherokee. It has 4.88s and a torqmasters locker in the front. I do water crossings a lot so I have to change the oil frequently.

The only thing that would concern me there is possible foaming issues from water dilution. Likely not a major issue being a differential, but something to think about.

 

[wpod]

For decades new semi trucks came from the factory with syn oil in the diffs and trannys.

 

[PontiacHO]

All good. Thanks for understanding.

I've spoken to Eaton twice about this. The first time, they told me it was due to the lower friction coefficient of synthetic oil causing issues with the helical gear LSDs. The second time I was told "synthetic is too thin" which is just ridiculous and made me not want to buy from them again.

The first one I disagree with since the friction coefficient between group II conventional and group III and IV synthetic is not that much different. In a sliding couple with borided surface vs rotation speed, the difference between conventional and synthetic is ~0.010 (0.165 vs 0.155) after ~8 minutes at 20 Mpa load.

See white paper titled "Experimental Analysis of Tribological Processes in Friction Pairs with Laser Borided Elements Lubricated with Engine Oils" published in December 2020. https://www.mdpi.com/1996-1944/13/24/5810/pdf

The second reason they gave is just asinine. It takes 30 seconds to google and disprove that one. A 90 grade gear oil is a 90 grade gear oil viscosity regardless of the base oil.

Where the issues with the helical gear LSDs would show in elastohydrodynamic lubrication down to boundary lubrication which is where the additives play much more of a role than the base oil. What they likely don't want people doing is buying something like Mobil 1 LS 75W-90, which contains a friction modifier additive package, that will alter the dynamic friction of the gears under load. They don't want people using the FM, not the base oil. There are synthetic base oils that don't contain a FM pack. Red Line 75W-90 NS and Amsoil Severe Gear 75W-90 are good examples of synthetic gear oils that do not contain (or contain very little) that FM pack.

Ok that certainly makes sense.
Thanks for your explanation and research.
See I don’t know everything like I think I do sometimes!

 

[73Duster]

How to select a good gear oil based on VI index.

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https://www.machinerylubrication.com/Read/28956/lubricant-viscosity-index

High or Low Viscosity Index needed?

If conditions are not constant (variable loads, variable speeds, variable ambient temperatures, etc.), then there is a need for not only the optimum viscosity but also a high viscosity index to stabilize the optimum viscosity. The more variable the conditions, the greater the need for high VI oils.

Also, keep in mind that for a great many machines there has been no past experimental or theoretical effort to identify the optimum viscosity. Viscosity selection is more of a wild guess. This too calls for a high VI lubricant.

A lubricant may merit having a high VI for one or more of the following reasons:

The optimum viscosity is not known
Varying loads and speeds exist
Varying ambient temperatures exist
To boost energy efficiency
To boost oil service life (lower average temperature)
To boost machine service life (fewer repairs and downtime)

Cheaper, lower VI lubricants may make sense if:

Speeds and loads are constant
Temperature is constant (constant ambient temperature or a heat exchanger is in use)
The optimum viscosity at the operating temperature is known and is consistently achieved

For 75w90 oils; from 2020

Mobil 1 syn gear oil has a VI of 146.
https://www.mobil.com/en/lubricants...cts/products/mobil-1-syn-gear-lube-ls-75w-90/

checking some others, Valvoline syn has a VI of 150.
https://sharena21.springcm.com/Publ...2d889bd3/cf662252-0bbd-e711-9c12-ac162d889bd1

Peak Auto syn has VI of 162 and has the lowest cost.
https://peakauto.com/wp-content/upl...ant_Oil_75W90_75W-140_Oil_Spec_Sheet_2016.pdf

Amsoil severe gear has VI of 166.
https://amsoilcontent.com/ams/lit/databulletins/g2043.pdf

Amsoil long life has VI of 143.
https://amsoilcontent.com/ams/lit/databulletins/g2042.pdf

 

[The Critic]

Amsoil Severe Gear 75W-90 are good examples of synthetic gear oils that do not contain (or contain very little) that FM pack.

Amsoil contains less FM than M1? Both advertise LSD compatibility.

(Perhaps this is why some people report needing to add additional FM with some brands, but not others.)