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| Member |
I know this is going to stir a debate but the rest of the internet has me confused and overthinking. I own a 2005 GMC Sierra 2500HD 4WD with the Duramax and Allison. I'm going to change out the oil in both differentials. I've settled on 75-90 synthetic to put in both. My question is which brand to use. Amsoil severe gear, Mobil 1, Royal Purple, Redline....so many options. Any help would be appreciated. Thanks, CT | ||
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| Member |
Mobil 1 is not rated for some diesels, so I would count that out. I just would not trust that it would be heavy duty enough for the gear mechanisms. Which brand matters little, what is more important is that you change it occasionally. If you have limited slip in either differential, you should stick to what the factory says. -c1steve | |||
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| Non-Miscreant |
If memory serves me, Mobil 1 makes two thickness of the gear grease. One is to replace 90w and the other for like 140 or 150w. I don't think the powerplant makes a bit of difference. They use the same differentials for both. The mere fact that you care enough to change it means those will probably last forever. The worst duty is in diffs that get submerged launching boats. Those often run at highway speeds for hours on end, then get dunked in cool or cold water. It contracts and water gets sucked past the seals. Unhappy ammo seeker | |||
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| Member |
Thanks for the reply. According to the code list in the glovebox, my truck has the locker in the rear. Service manual calls for 75w-90 synthetic in the rear and 80w-90 in the front. There shouldn't be a reason to not use synthetic in the front, should there? Thanks, CT | |||
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| Edge seeking Sharp blade! |
Redline or Motul if you want the best. All are good. | |||
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| Member |
Thanks for the reply. No boats or driving through water for me. I have enough problems as it is with out boat maintenance to pay for! CT | |||
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Shorted to Atmosphere |
You should be just fine running 75w-90 synthetic in both. Brand really doesn't matter as long as it is up to manufacturers specs. Then change it more often. I like to change my stuff on a severe duty cycle, just in case. I use the Mobil 1 without any issues. | |||
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| Member |
Thanks for the reply. CT | |||
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| Honor and Integrity |
I'm partial to the AMSOIL 75-90 severe gear, because I'm an AMSOIL Dealer. If you like technical reading, AMSOIL did a white paper called "A Study of Automotive Gear Lubes" (G2457). They tested 14 different gear lubes in this study. | |||
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Member |
Synthetic is better always. I used synthetic in one old car that didn't call for it. Be sure to add any "modifier" if specified by the manufacturer, even if the gear oil you buy says it's already rated for limited slip. Lover of the US Constitution Wile E. Coyote School of DIY Disaster | |||
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"Member" |
How does the differential know it's a diesel? _____________________________________________________ Sliced bread, the greatest thing since the 1911. | |||
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| Member |
Email sent to the email in your profile Thanks, CT | |||
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| Member |
By listening to the sound of the engine.  | |||
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Drill Here, Drill Now |
Mobil 1 is for passenger cars and light duty trucks, and Mobil Delvac 1 is for heavy duty applications. As a comparison, Mobil Delvac 1 75W-90 meets a longer list of industry specs than Amsoil Severe Gear 75W-90. The OP should look in his owner's manual and see what spec is required (e.g. API GL-5/MT-1) and find a 75W-90 from a reputable company (Mobil Delvac 1, Amsoil Severe Gear, Valvoline SynPower, Castrol Syntec, etc) Ego is the anesthesia that deadens the pain of stupidity DISCLAIMER: These are the author's own personal views and do not represent the views of the author's employer. | |||
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Cynic |
It's not going in the engine _______________________________________________________ And no, junior not being able to hold still for 5 seconds is not a disability. | |||
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| Raised Hands Surround Us Three Nails To Protect Us  |
Amsoil is my go to for differentials and transfer cases all get done every 50k Miles. ———————————————— The world's not perfect, but it's not that bad. If we got each other, and that's all we have. I will be your brother, and I'll hold your hand. You should know I'll be there for you! | |||
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I'll use the Red Key |
I use all Redline in my mustang (eng,tran,diff). The gear oil has friction modifiers in it for limited slip differentials, they sell a 4 oz bottle and I would put that in too. I would use synthetic front and rear. https://www.redlineoil.com/ Donald Trump is not a politician, he is a leader, politicians are a dime a dozen, leaders are priceless. | |||
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Member |
I used Valvoline synthetic in my 2002 Chevy Duramax. I used the 75W-90, didn't tow a lot so I didn't use the 75W-140 in the rear diff. Worked fine, IIRC I didn't need friction modifiers. Living the Dream | |||
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member |
I doubt it knows it is a diesel, but it certainly knows there is a lot more torque being applied to the pinion and ring gears. | |||
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| Member |
I'm an amateur tribologist, with no professional credentials in this field, just a great interest for the past 40 years... I would read the manual and make sure whatever you use meets those specifications, including the viscosity grade. Of the brands you mentioned, assuming they meet the specifications, Amsoil Severe Gear, Mobil 1, and Red Line are all outstanding lubricants, among the best in the industry. I've been using Amsoil Severe Gear for the past 10+ years with good results. | |||
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