Are all full synthetic rear differential gear fluids made equal?

[4WD]

I think you could use any major brand that meets specs, including Supertech, and never know a difference. UNLESS you are towing heavy loads, i think thats where Amsoil, HPL, Redline etc, might be a good choice.

Those are top shelf - and the Mobil Delvac 1 that I run - made for heavy trucks and equipment is also very popular with the Porsche track crowd - so that’s why I started using it years ago in G80’s …
Normally get it from Summit along with enough stuff to get free shipping

 

[Rand]

Care to expand on the Lucas and corrosion testing part of what you posted? I’m not familiar.

I forget the exact specifics an independent company did corrosion testing on yellow metal strips(maybe for amsoil?).. the lucas failed alarmingly.. but it might be out of date.. they could have improved their product.. or not.

disclaimer: not a fan of anything lucas brand.

I'll stand by my claim of anything major name brand(or not so major) and syn being a good choice.
except applications that require specifics.. such as subaru transmissions that required GL-5 but also FM for manual transmission etc.

Supertech is good.. esp if you want to spend 5$ on some 75w90.

Motul, amsoil, and redline are all top tier products..
and m1, shell etc cant go wrong for standard applications.

 

[BigGeo]

I forget the exact specifics an independent company did corrosion testing on yellow metal strips(maybe for amsoil?).. the lucas failed alarmingly.. but it might be out of date.. they could have improved their product.. or not.

disclaimer: not a fan of anything lucas brand.

I'll stand by my claim of anything major name brand(or not so major) and syn being a good choice.
except applications that require specifics.. such as subaru transmissions that required GL-5 but also FM for manual transmission etc.

Supertech is good.. esp if you want to spend 5$ on some 75w90.

Motul, amsoil, and redline are all top tier products..
and m1, shell etc cant go wrong for standard applications.

I believe using GL5 in applications that call for GL4 can cause corrosion of soft metals in manual transmissions . The YouTube “Car Care Nut” has a discussion concerning this issue: Which fluid to use for Toyota Diffs,Transfer Case and Manual transmissions.

 

[rav]

After I did some internet searching, what I found was that Amsoil Severe 75W90 was the only 100% synthetic GL5 gear oil. Others just say synthetic oil. Most tests comparisons show AMSOIL at or near the top of the list.

 

[Rand]

I believe using GL5 in applications that call for GL4 can cause corrosion of soft metals in manual transmissions . The YouTube “Car Care Nut” has a discussion concerning this issue: Which fluid to use for Toyota Diffs,Transfer Case and Manual transmissions.

Most GL5 or dual spec gl4/gl5 for use in a Manual transmission wont.. but the shift quality might be terrible.
and its unneeded because nothing requires that level of EP almost all manual transmissions (cars and light trucks)
However some applications require GL5 in a manual transmission...

 

[vwmaniaman]

I have been using Royal Purple in my truck that I tow with. Also in our one ton Roadtrek camper van. Have had no problems.

 

[XCIDMigs]

Gimpy1 is right. As long as the fluid are all the same specification, the real difference is the amount of Limited Slip Additives in them. Motul has both with and w/o SL added gear fluids. The real question is what type of rear differential is on your car and what is the manufacture's specification/requirement for the differential. When in doubt, you can't go wrong with OEM fluid.

https://www.motul.com/us/en-US/products/gear-300-75w90

https://www.motul.com/us/en-US/products/gear-300-ls-75w90

If you have any type of non open dif you definitely need to use what is speced, Jeep with the quadradrive has some weird additive, my GM truck with E lockers also has a non additive spec for it which is very important it will not work correctly with LS fluid added in.

 

[2000Trooper]

Change it every 30k and you’re better off than what brand you use.

 

[sohccammer427]

If you take 75W-90 API GL-5 for example some are labeled as being LS (limited slip) and others don't mention it or even say does not contain any friction modifiers. Best I an tell Delo Syn-Gear XDM 75w-90 makes no mention of LS, while some like Mobil1 actually call it Syn Gear LS 75w-90.

Wish I knew more about it. Guess you'd really need to know what your diff or gearbox called for?

 

[sohccammer427]

Which begs the question... Does the GL-4, GL-5 category by definition require that the oil contain a certain amount of friction modifiers?

If an application called for GL-5, would that in itself be all one would have to worry about?

 

[tblt44]

Mobil 1 75w 90 comes out clean in my 10 bolt after 60k.
This is for the first 2 changes when it was new

 

[MolaKule]

Which begs the question... Does the GL-4, GL-5 category by definition require that the oil contain a certain amount of friction modifiers?

Good question.

The GL-5 rating is in essence a "protection" rating against wear, galling, and other problems for a specific type of gearset, a heavily loaded gearset such as a differential.

You could have a fluid with a GL-4 rating but that does not mean it is a proper fluid for a Manual Transmission, an MTF.

If an application called for GL-5, would that in itself be all one would have to worry about?

If the label of a GL-5 gear lubes says LS then it contain a friction modifier for clutch type Limited Slip differentials. If it does not say LS, then you may have to add an aftermarket friction modifier to it.

Please understand, the friction modification chemistry for a GL-5 LS is entirely different than one for a GL-4 MTF.

 

[MolaKule]

Are all full synthetic rear differential gear fluids made equal?

I assume you mean synthetic lubricants formulated for a GL-5 rating.

All synthetic GL-5 Gear lubes must meet minimum criteria for wear under loading, rust prevention, maximum foaming, corrosion protection, etc.

All conventional (mostly mineral oil-based) GL-5 Gear lubes must meet the same minimum criteria stated above.

Performance wise, no matter the formulation, they all have to meet the same minimum criteria.

Now, if the question is: Do all brands of synthetic GL-5 gear lubes contain the same Formulation, the answer is NO. Different formulation approaches with different chemistry can achieve the same performance criteria.

There are an infinite number of ways I can formulate any gear lube, but to market it as a GL-5 gear lube, the totality of the chemistry (Base oils and additive package) must meet the minimum performance and testing requirements set forth by the SAE using various ASTM testing methods.

 

[The Critic]

There are an infinite number of ways I can formulate any gear lube, but to market it as a GL-5 gear lube, the totality of the chemistry (Base oils and additive package) must meet the minimum performance and testing requirements set forth by the SAE using various ASTM testing methods.

If you were to speculate on the variations in performance amongst the available "Full-synthetic" 75W90's, would the differences be comparable to the differences found within the various API SP engine oils?

 

[MolaKule]

If you were to speculate on the variations in performance amongst the available "Full-synthetic" 75W90's, would the differences be comparable to the differences found within the various API SP engine oils?

I prefer to deal with actual test data and not speculate.

One would have to test for the variances in all of the marketed synthetic 75W90 gear lubes and all of the marketed API SP oils to arrive at any conclusion.

 

[Oily_Thing]

Honda's fluid for the Ridgeline is not the same.

 

[MolaKule]

Honda's fluid for the Ridgeline is not the same.

Which fluid? Please explain.

One line sentences don't tell us anything.

 

[BMW Dom]

This is like asking if all synthetic oils are the same. If it meets the requirement, then it is good enough.

 

[4MUL8R]

There is a big difference between GL4 and GL5 specifications.

Do not use GL4 lubricants where GL5 lubricants are specified. Insufficient EP protection in GL4 will potentially harm any hypoid axle gear. Insufficient antiwear protection in GL4 will potentially harm axle gears and axle gear bearings.

The GL4 specification has been obsolete for many many years. The tests outlined in GL4 cannot be performed, any more, as defined in the specification. Test hardware is no longer available, and the stated methods are not performed. However, substitute tests that explore the same measurements made in the GL4 specification are presently used to validate a GL4 lubricant, with no known issues in hardware requiring GL4 protection.

Judging between synthetic gear lubricants is challenging. If the lubricants only claim GL5, absent a full test lab, one could not ascertain any differences. If lubricant A claims GL5, and lubricant B claims GL5 and some OEM specification, lubricant B would have more and different performance testing behind it.

Brands such as AC Delco and Motorcraft have far more challenging test requirements than GL5. Tests are proprietary, and expensive.

 

[kschachn]

API GL-4 is a current specification and has not "been obsolete for many years." Where are you getting that information? That whole part about not being able to be tested is also not correct.