3 different 75w/90 gear oils, are they all similar enough?
3 different 75w/90 gear oils, are they all similar enough?
(OP)
Hey all,
Having an issue trying to determine if gear oil C is similar enough to be a replacement for A and B. Oils A & B are both Porsche Approved for use in their trans axles and differentials but they are generally difficult/expensive to purchase. All 3 of them are GL5 rated but Porsche does not specifically ask for GL5 they only want you to use oil A & B.
Oil C is recommended by it's own manufacturer for use in Porsche transaxles & differentials. Below I am listing the data/specs that I could find for all 3 and I have looked at many other GL5 oils as well. It seems that the bigger difference with these three oils from other GL5 75w/90 gear oils is these 3 seem to have lower viscosity at lower temps while still having higher flash points than others I have seen. Also the two approved oils A and B seem to have a lower Brookfield -40 C Viscosity than oil C as well as other oils I have looked at.
How big of a difference would this Brookfield/dynamic viscosity make in actual use. Is oil C close enough that it could be used in place of A & B?
I appreciate any and all feed back.
Thank you in advance!
A:
SAE Grade 75W-90
Viscosity, cSt at 40 ºC 77.2
Viscosity, cSt at 100 ºC 14.5
Viscosity, cSt at 0ºC (measured) 590
Viscosity Index 197
Brookfield Viscosity at -40 ºC, cP 20,000
Pour Point, ºC -48
Flash Point, ºC 212
Copper corrosion, 3 hr at 150ºC 1B
B:
SAE J 306 75W-90 SAE Viscosity Grade
0 2 ISO 3104 81 Kinematic Viscosity @40 C mm /s
0 2 ISO 3104 14.9 Kinematic Viscosity @100 C mm /s
ISO 2909 194 Viscosity Index
ISO 9262 35000 Dynamic Viscosity mPa s
0 3 ISO 12185 879 Density @15 C kg/m
0 ISO 2592 205 Flash Point (COC) C
0 ISO 3016 -45 Pour Point C
C:
Specifications and approvals:
API GL5 · MIL-L 2105 C · MIL-L 2105 D
Technical data
SAE class (gear oils) 75W-90
SAE J306
Density at 15 °C 0,855 g/cm³
DIN 51757
Viscosity at 40 °C 80,9 mm²/s
ASTM D 7042-04
Viscosity at 100 °C 14,3 mm²/s
ASTM D 7042-04
Viscosity at -40°C (Brookfield)
<= 150000 mPas
ASTM D 2983-09
Viscosity index 184
DIN ISO 2909
Pour point -60 °C
DIN ISO 3016
Flash point 190 °C
DIN ISO 2592
Color number (ASTM) L 1,0
DIN ISO 2049
Having an issue trying to determine if gear oil C is similar enough to be a replacement for A and B. Oils A & B are both Porsche Approved for use in their trans axles and differentials but they are generally difficult/expensive to purchase. All 3 of them are GL5 rated but Porsche does not specifically ask for GL5 they only want you to use oil A & B.
Oil C is recommended by it's own manufacturer for use in Porsche transaxles & differentials. Below I am listing the data/specs that I could find for all 3 and I have looked at many other GL5 oils as well. It seems that the bigger difference with these three oils from other GL5 75w/90 gear oils is these 3 seem to have lower viscosity at lower temps while still having higher flash points than others I have seen. Also the two approved oils A and B seem to have a lower Brookfield -40 C Viscosity than oil C as well as other oils I have looked at.
How big of a difference would this Brookfield/dynamic viscosity make in actual use. Is oil C close enough that it could be used in place of A & B?
I appreciate any and all feed back.
Thank you in advance!
A:
SAE Grade 75W-90
Viscosity, cSt at 40 ºC 77.2
Viscosity, cSt at 100 ºC 14.5
Viscosity, cSt at 0ºC (measured) 590
Viscosity Index 197
Brookfield Viscosity at -40 ºC, cP 20,000
Pour Point, ºC -48
Flash Point, ºC 212
Copper corrosion, 3 hr at 150ºC 1B
B:
SAE J 306 75W-90 SAE Viscosity Grade
0 2 ISO 3104 81 Kinematic Viscosity @40 C mm /s
0 2 ISO 3104 14.9 Kinematic Viscosity @100 C mm /s
ISO 2909 194 Viscosity Index
ISO 9262 35000 Dynamic Viscosity mPa s
0 3 ISO 12185 879 Density @15 C kg/m
0 ISO 2592 205 Flash Point (COC) C
0 ISO 3016 -45 Pour Point C
C:
Specifications and approvals:
API GL5 · MIL-L 2105 C · MIL-L 2105 D
Technical data
SAE class (gear oils) 75W-90
SAE J306
Density at 15 °C 0,855 g/cm³
DIN 51757
Viscosity at 40 °C 80,9 mm²/s
ASTM D 7042-04
Viscosity at 100 °C 14,3 mm²/s
ASTM D 7042-04
Viscosity at -40°C (Brookfield)
<= 150000 mPas
ASTM D 2983-09
Viscosity index 184
DIN ISO 2909
Pour point -60 °C
DIN ISO 3016
Flash point 190 °C
DIN ISO 2592
Color number (ASTM) L 1,0
DIN ISO 2049





RE: 3 different 75w/90 gear oils, are they all similar enough?
je suis charlie
RE: 3 different 75w/90 gear oils, are they all similar enough?
Porsche is known to be very clear in specifying which lubricants to use since they have experienced that oils that do meet requirements of main stream applications not always are up to scratch when used in their vehicles. therefore i would stick to the oils approved to minimize the risk of (very) costly repairs in future in this case.
the approved oils may be costly too, but you only need a few litres and they will not need to be changed that often.
RE: 3 different 75w/90 gear oils, are they all similar enough?
If this car is PDK or DCT, then you have even less choice- those cars should see factory fill and factory fill only.
RE: 3 different 75w/90 gear oils, are they all similar enough?
Thanks VERY much for the replies.
Gruntguru, actually no the vehicle(s) won't see cold temps (I am in South Florida).
romke, this is what I was mainly concerned about; that the warm/running viscosity of all three are pretty close but the 2 approved oils have a very different cold viscosity my thought was that there is probably more to it and and that there is a reason(s) in this particular case that no other oils are approved.
jgKRI, car is a manual trans, I have no problem at all paying more for the correct approved lubricant and I have always lived by this rule especially in high end cars like this. The only reason I even bothered to look at other oils was because many very large Porsche specific supply houses and Porsche specific repair shops not only recommend but install in their customers' cars non-approved gear oils in these same applications that I am looking at. It was only after I looked more closely at the data sheets that I realized in colder tests only the approved oils seem to have this property which is why I came here looking for more opionions.
BTW, oil C was the only one that I found after really looking that actually comes close to A & B in the warm/operating temps. The other oils that I have seen recommended and/or used by Porsche specific shops are even higher viscosity across the board! No wonder some folks are complaining about notchy shifting,especially when cold
Again, I want to thank you all for the replies. You have confirmed what I was thinking and made my decision very easy. I will only go with an approved oil for this application. Thanks!!!
RE: 3 different 75w/90 gear oils, are they all similar enough?
je suis charlie
RE: 3 different 75w/90 gear oils, are they all similar enough?
RE: 3 different 75w/90 gear oils, are they all similar enough?
High VI is not all beer and skittles. VI improvers generally compromise other attributes.
je suis charlie
RE: 3 different 75w/90 gear oils, are they all similar enough?
Am I understanding your point correctly?
BTW, I have re-read the requirements by Porsche and they specifically mention that Viscosity, cSt at 0ºC must be less than 600. Not sure if this makes any difference to your point.
Thanks again for all the feedback.
RE: 3 different 75w/90 gear oils, are they all similar enough?
A. 535
B. 577
C. 618
Excerpt from Link
"Unfortunately, viscosity index improvers do have some drawbacks. The primary disadvantage is they are susceptible to mechanical shearing. When referring to the slinky analogy, it is easy to imagine a stretched-out slinky cut in half by mechanical processes to produce two shorter slinkys.
As the additive is repeatedly sheared, it loses its ability to act as a more viscous fluid at higher temperatures. Higher molecular weight polymers make better thickeners but tend to have less resistance to mechanical shear. Lower molecular weight polymers are more shear-resistant, but do not improve viscosity as effectively at higher temperatures and, therefore, must be used in larger quantities."
je suis charlie
RE: 3 different 75w/90 gear oils, are they all similar enough?
another consideration might be high temperature use - driving on highways with high speeds for a long time. under those circumstances high temporary shear may occur effectively lowering the viscosity temporarily to a value that no longer is able to protect the gear surface sufficiently against wear. temporary shear only occurs when using VI improvers, using high quality baseoils without VI improver can avoid the phenomenon. in the SAE engine oil viscosity specifications there is used a special test to assess whether the oil withstands high temperature/high shear conditions at 150 deg C, about the operating conditions that may be expected in the valve actuation mechanism (cams, followers).
there are thus several reasons to limit the amount of VI improver in a finished product and the only way to do that is to start out with better quality baseoils - that are unfortunately more expensive due to more processing steps that are involved..
RE: 3 different 75w/90 gear oils, are they all similar enough?
je suis charlie
RE: 3 different 75w/90 gear oils, are they all similar enough?
If I was to send off a sample of 2 of the oils to a service like Blackstone for an analysis would this information help us to make a better decision or would an analysis like this still not reveal the actual make up of the products and what makes them different?
Thanks!