Warning: This post might take awhile, just like trying to find a fluid that meets the 9986115 spec. other than GM's grape-scented liquid gold. I have researched past posts thoroughly. To avoid the drawn-out explanation and see an actual question, scroll down to the bottom.
Here goes:
2001 Silverado 1/2 ton with G80 "locking" rear. Manual specifies part #12378261 "or equivalent meeting" the above specification. I was going to order the GM stuff from GM Parts Direct for $16, but they say they can no longer ship it because the bottles aren't sealed correctly. I contacted Red Line, Royal Purple, and Amsoil asking specifically if their fluids are approved for the GM number, since that spec is not listed anywhere on their web sites or bottles. I also e-mailed Eaton to ask what special requirement the GM specification meets, and whether any alternative oils will satisfy it--Have not yet heard from Eaton.
The oil manufacturers all say their fluids will work, but not that they offcially meet GM 9986115. Here are the replies :
Royal Purple:
"Yes, your Differential takes
Max Gear 75W90 ( No modifiers are needed)"
Red Line:
"Thank you for contacting Red Line Oil, the GM
9986115, pt.# 12378961 is a non friction modified 75W90 synthetic gear oil. The 75W90NS would match the frictional characteristics of the spec. What GM is saying is that an additional friction modifier isn't needed. The 75W90 contains a friction modifier, it wouldn't be harmful to the unit and is beneficial as it will reduce the friction and temperatures of the differential."
Amsoil sounds a little more definite:
"In response to your inquiry, yes AMSOIL Synthetic Severe Gear 75W90 Gear Lube (SVG) does meet the GM spec’s. The data sheet on our website in the most current. The all product lookup guide is going to be updated shortly and SVG will then be shown for your application."
Since the website does not mention the actual GM number, I wrote back and asked Amsoil to mail me an updated, printed data sheet that does mention approval.
Here's the reply:
"The Severe Gear TSBB states it meets many specifications for semi-trucks and also states 'plus hypoid gear oil specifications from all foreign and domestic manufacturers such as GM, Ford and Daimler Chrysler.' This includes GM 9986115."
So all this seems to put me back at the beginning--everybody says their oil will work, but actual approval for the GM spec does not appear anywhere in writing, except the Amsoil e-mail.
Maybe I'm overly paranoid, but I don't want to use a fluid that will harm the differential, which seems possible according to some earlier posts. Or maybe GM's mysterious spec is meant only to scare people into shelling out $30 for a quart of fluid. A few posts by Molakule suggest that the difference is not in performance but in other companies paying GM for licensing.
Finally, here are my questions:
1. Can anybody tell me what the GM number requires, other than grape fragrance?
2. Does anyone know of an aftermarket oil that actually, in writing, meets the GM Spec?
3. Am I making an ordeal over this, when I could really just throw in any synthetic 75W-90 and be fine?
4. If you are using Royal Purple or Redline in a late-model truck G80, could you post how they're working and mileage since the change? I'm sure Specialty Formulations and Amsoil are fine oils, but I can get the other two locally. I'd like to avoid shipping charges if all other factors are equal.
This may not clarify the issue any more than previous posts have, but thanks to all for input and for taking the time to read.
Here goes:
2001 Silverado 1/2 ton with G80 "locking" rear. Manual specifies part #12378261 "or equivalent meeting" the above specification. I was going to order the GM stuff from GM Parts Direct for $16, but they say they can no longer ship it because the bottles aren't sealed correctly. I contacted Red Line, Royal Purple, and Amsoil asking specifically if their fluids are approved for the GM number, since that spec is not listed anywhere on their web sites or bottles. I also e-mailed Eaton to ask what special requirement the GM specification meets, and whether any alternative oils will satisfy it--Have not yet heard from Eaton.
The oil manufacturers all say their fluids will work, but not that they offcially meet GM 9986115. Here are the replies :
Royal Purple:
"Yes, your Differential takes
Max Gear 75W90 ( No modifiers are needed)"
Red Line:
"Thank you for contacting Red Line Oil, the GM
9986115, pt.# 12378961 is a non friction modified 75W90 synthetic gear oil. The 75W90NS would match the frictional characteristics of the spec. What GM is saying is that an additional friction modifier isn't needed. The 75W90 contains a friction modifier, it wouldn't be harmful to the unit and is beneficial as it will reduce the friction and temperatures of the differential."
Amsoil sounds a little more definite:
"In response to your inquiry, yes AMSOIL Synthetic Severe Gear 75W90 Gear Lube (SVG) does meet the GM spec’s. The data sheet on our website in the most current. The all product lookup guide is going to be updated shortly and SVG will then be shown for your application."
Since the website does not mention the actual GM number, I wrote back and asked Amsoil to mail me an updated, printed data sheet that does mention approval.
Here's the reply:
"The Severe Gear TSBB states it meets many specifications for semi-trucks and also states 'plus hypoid gear oil specifications from all foreign and domestic manufacturers such as GM, Ford and Daimler Chrysler.' This includes GM 9986115."
So all this seems to put me back at the beginning--everybody says their oil will work, but actual approval for the GM spec does not appear anywhere in writing, except the Amsoil e-mail.
Maybe I'm overly paranoid, but I don't want to use a fluid that will harm the differential, which seems possible according to some earlier posts. Or maybe GM's mysterious spec is meant only to scare people into shelling out $30 for a quart of fluid. A few posts by Molakule suggest that the difference is not in performance but in other companies paying GM for licensing.
Finally, here are my questions:
1. Can anybody tell me what the GM number requires, other than grape fragrance?
2. Does anyone know of an aftermarket oil that actually, in writing, meets the GM Spec?
3. Am I making an ordeal over this, when I could really just throw in any synthetic 75W-90 and be fine?
4. If you are using Royal Purple or Redline in a late-model truck G80, could you post how they're working and mileage since the change? I'm sure Specialty Formulations and Amsoil are fine oils, but I can get the other two locally. I'd like to avoid shipping charges if all other factors are equal.
This may not clarify the issue any more than previous posts have, but thanks to all for input and for taking the time to read.
