mineral base oils better in gear oils?

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Jasper Engines thinks so. To keep their warranty on an axle assembly you buy from them they ask that you use the Shell dino gear oil that they send with the units. And they want you to use it on replacement also.
 
I keep hearing this but have never gotten a satisfactory explanation as to why. Gp II base oils do hold additives very well... possibly better than syns and gear oils are all about boundary lubrication so that's an important aspect. I'm not sure what "pressure-viscosity coefficients " are exactly but I guess that makes for an interesting bit of research.
 
My experience tells me that's balony. Most pickups come with synthetic gear lube in their diffs and also many big trucks(18 wheelers) come with synthetic gear lube as well. Synthetics will lower the diff temps, last much longer between changes, and reduce wear compared to dino. Now if dino was better wouldn't you think these manufactures would know that?
 
Hi,
friendly_jacek - Well all sorts of stories abound - this is the real World. I can tell you that my experiences over several decades debunks this arguement. That said, there may be certain applications (severe shock loading) where mineral based gear lubricants may have an advanyage

I my experience and in the experience of Eaton Corp (Reference back to 8/93) synthetic gear lubricants offer huge advantages over mineral gear lubricants. This relates to lowering operating temperatures and tolerating much higher operating temperatures. Seal life is greatly enhanced as is low temperature gear selection and with lower cold "drag"

This was confirmed by me in actual operations over many many millions of kiliometers in many vehicles and covering very low and very high loads/temps and in severe use applications. I had such lubricants in individual use for "whole of life" (up to around 2m kms) using UOAs and Manufacturer's condemnation OC levels

ZF and MB found this too many years ago in their heavy vehicle equipment/Divisions

Be careful what you read on the Internet......................be very careful about what you believe!!!
 
As usual, people are commenting on a quote taken out of context. Read the whole article and learn how people decide what gear oil to use when no OEM recommendation is available for the machinery being used.
 
Thanks, reading some more, sounds like synthetic gear lubricants are superior at high or low temps, bur slightly inferior at mild to moderate temps near 50C. However, the difference is not huge and easily offset by increased OCI and efficiency.
 
Hi,
friendly_jacek - The advantages of synthetic gear lubricanst are real for most users.
Suprisingly most diffs and gearboxes run quite cool - too cool in many cases IMO

Im my heavy trucks the "normal" temperatures were expected to be around 120C with the warning level at 150C. Mostly the semi-trailers were at 42.5t

In reality the average gearbox temp was 86C, front diff (tandem drive) 90C and the rear diff 94C. The maximum recorded was 100C on a long climb (ambient 28C) (gearbox and front diff) and the lowest was 60C (gearbox) on a flat road at 35C ambient

All ideal for synthetic lubricants - overall the ambients here ranged from -10C to 45C

When running synthetic gear lubricants over many years I never experienced any wheel bearing failures which are quite common in the trucking industry!
 
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Towing my enclosed trailer (8,000 lbs) back to San Diego with my motorhome (Ford F53 460 cu in, 4 speed auto, gearvendors)one very hot summer day I was in a big hurry and keeped it floored until I got to the top of the mountain grade, about 13 miles. I smelled a funny odor when I got home and looked underneath. The diff housing had turned a dark color from overheating and the sway bar bushings that bolt to it were melted. Amsoil 75-140 was in the diff and no ill effect came from it other than the melted bushgings. I looked at the oil and it looked like the day I put it in. I suspect mineral oil would have left my on the side of the road with destroyed gears.
 
A friend called today to tell me he got his 94 Dodge Ram 4WD truck back from a rear axle/transfercase/manual gearbox specialist guy I had sent him to locally. He was telling me how happy he was with the rear axle rebuild job that he had done. He mentioned that this guy did not believe in synthetic gear oils, and I remember this from before. He worked for Richmond gear in Liberty, SC for 30 years before going out on his own. He builds race axles, etc too. His work is excellent and prices reasonable.

He put a limited slip diff in another friend's 2500 Silverado and refilled with Lucas conventional gear oil. It was the non-clutch (gear only) type of LS unit, and it chattered like crazy on off ramps after a good hot run on the interstate. My friend replaced the Lucas with some of that synthetic purple gear oil and problem solved... never chattered again. He never called and told the builder like I suggested. I would think that would have been some useful feedback.
 
I have seen neglected, yet quiet diffs and gearboxes' lubes replaced with synthetic lubes and then leak or fail later. Not sure if the syn lube was involved or what. So, I much prefer to change lubes or replace with syn before lube degrades too far or too much wear material has built up in the lube and the unit. If an automotive diff has been neglected for 200k miles or more, it may be best to just keep it full and save money for the inevitable rebuild. It may just hold up until something else causes one to replace the vehicle.

Also, I like the Schaeffers Syhnthetic Plus 75W-90 GL-5. It is a blend of PAO and Group II or II+ I believe, so maybe it is the best of both worlds? It is by far my favorite GL-5 75W-90.
 
Originally Posted By: Doug Hillary


Im my heavy trucks the "normal" temperatures were expected to be around 120C with the warning level at 150C. Mostly the semi-trailers were at 42.5t

In reality the average gearbox temp was 86C, front diff (tandem drive) 90C and the rear diff 94C. The maximum recorded was 100C on a long climb (ambient 28C) (gearbox and front diff) and the lowest was 60C (gearbox) on a flat road at 35C ambient



Like I said, over 60C synthetic are better. Under 60C, mineral are better.

Backup_200403_lubeselect-tab2.gif
 
LOL, found good post on mineral gear oils here:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1105621

Quote:
"IMHO the RedLine differential gear oil's are way too thin..... whether or not they say 90-140 or not. It doesnt have the 'film pressure strength' that is pretty manditory for a street driven chassis. My first experience with this was back in the late 80's during the "Corvette Challenge Series". RedLine was a sponsor and we tried their entire line to include their gear oils... but found we had to change the "Shock Proof" differential oil in it every race. Not to mention its running temperature was above acceptable limits. If you were to use it in a track car... Id say go for it. But yours isnt... so I wont.

The best lubericants I have found in the past 15+ years or so are:

Schaffer suspended moly, straight 90wt. (Passenger cars, front ends in 4x4, light duty, cold climate).
Schaffer ISO9000 suspended moly, straight 140wt (Passenger cars and trucks, street performance, rear in 4x4, heavy duty, all climate).
Schaffer ISO9000 suspended moly, straight 250wt (Trophy trucks,Top Fuel, Funny Car, Pro Stock and maximum effort high HP applications, trucks up to 5ton).
TORCO SGO/RGO 85-140wt (If you really thought a multi viscosity really means something in a diff. BTW, it doesnt).
LE 704-9920 75-140wt (same as above).
Amsoil SG 75-140 (same as above).
Royal Purple 85-140wt (same as above).

The parrifin based oils are the ticket."


Spelling aside, that actually sums my bad experience with Redline 70W90 too.
 
My stream of conscience.

Film thickness is proportional to viscosity.
Viscosity changes with temperature, shear rate and pressure.
PAO synthetics thin more under pressure than mineral oil. (that is where pressure viscosity coefficient comes in)
Lower VI oils thin more with temperature increase.
Polymer enhanced (with VI improver) oils thin more under shear.
Gear oils contain not only base stocks but additives.
Additives are primarily responsible for wear under boundary conditions.
Base oils are primarily responsible for wear at hydrodynamic conditions.
The film thickness at which system goes from hydrodynamic to boundary is primarily related to part finish and smoothness.
Friction characteristics of friction modified is function of additives.
Synthetic can have the same friction and wear additives as mineral oils.
Just because oil thins does not mean it goes into boundary conditions.
So which is best for wear protection depends on where you begin and where you end up. Each can be better under different conditions.
BTW PAO synthetics almost always have a longer operating life with the same additives. Mineral oils almost always have better solubility seal swell.
 
Originally Posted By: DWC28
My stream of conscience.

Film thickness is proportional to viscosity.
Viscosity changes with temperature, shear rate and pressure.
PAO synthetics thin more under pressure than mineral oil. (that is where pressure viscosity coefficient comes in)
Lower VI oils thin more with temperature increase.
Polymer enhanced (with VI improver) oils thin more under shear.
Gear oils contain not only base stocks but additives.
Additives are primarily responsible for wear under boundary conditions.
Base oils are primarily responsible for wear at hydrodynamic conditions.
The film thickness at which system goes from hydrodynamic to boundary is primarily related to part finish and smoothness.
Friction characteristics of friction modified is function of additives.
Synthetic can have the same friction and wear additives as mineral oils.
Just because oil thins does not mean it goes into boundary conditions.
So which is best for wear protection depends on where you begin and where you end up. Each can be better under different conditions.
BTW PAO synthetics almost always have a longer operating life with the same additives. Mineral oils almost always have better solubility seal swell.


Well done summation!
 
I have had good luck using LE monograde mineral and mineral/synthetic blend gear oils in several rear diffs. But I can understand where someone might need or want a synthetic multi-vis gear oil for cold climates. I also understand that LE gear oils aren't your average off the shelf lube. Other than that. I think you should find one you like (syn or mineral) and stick with it.

For a part time front diff, I can understand synthetic as being preferred. 4X4 selection might require some umph to get out of a bad situation, and the lower viscosity (75W) might benefit the unit.

As far as RL 75W-90 goes, I haven't seen a good UOA yet.
 
Originally Posted By: DWC28

So which is best for wear protection depends on where you begin and where you end up. Each can be better under different conditions.


Okey?
 
Originally Posted By: INDYMAC

As far as RL 75W-90 goes, I haven't seen a good UOA yet.


I noticed that too. This is very surprising as the additive dose is 3x the standard gear oil.

It must be an issue with the base oil.
 
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