Which gear oil? 2005 yukon xl

Discussion in 'Maintenance & Upkeep' started by Pikey, May 15, 2013.

  1. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    I an going to change the gear oil in my rear diff today or tomorrow. My manual recommends 75w-90 synthetic gear oil. The only 75w-90 that I can find is for limited slip diffs, I have a G80 Gov-Loc. I am looking at using Mobile 1 75w-90, amsoil, or Mobile Delvac (if I can find quarts of it. alternatively it is $47 a gallon) I do tow a boat very often in the summer, but not very far. I have read of guys going to 75w-140 because they tow. Does anyone feel as if this is necessary? Any recommendations on which gear oil to use? I have read some bad things about Lucas and Royal Purple. I would consider amsoil. But, can not find a place near me that carries it or that I can get a significant discount at. I can pickup 3 quarts of Mobile 1 for $22 after discounts. Any suggestions? I may attempt to get a hold of @1st Synthetics and see what his prices are for the 75w-90. Looking online I can only buy amsoil in cases of 12.

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    I am going with amsoil, I will return the mobile 1 I just purchased. I spoke with Scott from 1st Synthetics and his prices for guys on the forum are pretty darn good. So, i will be driving down to get it tomorrow.
    Last edited: May 15, 2013
  2. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner 1000 Posts

    Glad you can get a good price on the amsoil. I usually use Mobil 1 for the rear (G80) and front
  3. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    Scott at 1st synthetics gives all forum members here wholesale pricing. :happy:
  4. steved

    steved Former Member

    I have owned several 2500s, mostly Dodge and now this Silverado.

    I always dump the factory fill early, and in the last two (the last Dodge and this Silverado) I used Mobil 1 75w90. I noted in the Dodge (and dumped the Mobil 1 early as a result) that the differential started whining with less than 10k miles on the oil. I swapped over to Royal Purple 85w140, and no more noise for the next 200k miles. I read all the reviews and it seemed Mobil 1 or Amsoil were the two choices for the Silverado and G80. Same thing, 10k miles (15k total) and the differential developed a noticeable whine.

    I happened onto a 5-gallon pail of Amsoil SVO (severe gear 75w140) for $50 a couple months ago...decided this weekend to swap out gear oil yet again. Differential is absolutely quiet now...not a noise.

    I am a firm believer that 75w90 is a fuel mileage/CAFE thing, and not adequate for a full size truck. I have had good luck with 75w140 and 85w140, and I will continue to run both.
  5. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    well, the fluid change is going to have to wait. I crawled under there and realized that there is no drain plug and the hole is directly next to the pinion so I can not get my mighty vac tube in there. Thanks GM! My 2002 had a drain plug. I don't have time today to pull the cover.
    Last edited: May 16, 2013
  6. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner 1000 Posts

    Fortunately mine has the drain plug. Never understood why they would not put one on there.
  7. Pikey

    Pikey Moderator Staff Member 5+ Years ROTM Winner 5000 Posts

    Well, I changed the fluid last night after class. There happens to be a parts store a few blocks away from my school. So, I went during break and grabbed the gasket. I am glad I changed it! It was pretty nasty and had the consistency of water. I assume that it had been done at least one time before because the way rtv sealer was spread all over the place. I did not think that I had rear end noise before. But, after changing the fluid it seems much quieter.

    All together it took me about an hour and a half. That is because my ocd kicked in. The cover was covered in flaking rust. So, I wire wheeled all the rust off, primed it with a self etching primer, and sprayed it with black paint. Unfortunately, the only black paint I had was high gloss. No one will see it under there anyway. I tend to go a little over board on things like this also. I drained the diff, sprayed everything down with brake clean, covered the gears in a plastic bag, and then cleaned the mounting surface, with a wire wheel on a dremel, until all rust and rtv was removed and the surface was nice and shiny, then removed the bag and resprayed everything, I cleaned the cover on my bench grinder. Then, I put a layer of rtv on both mating surfaces and applied the gasket. I know that many guys say that there is no need to do both gasket and rtv. I would rather use a $5 tube of rtv and a $5 gasket and not have to redo it because it is leaking.
    Last edited: May 17, 2013
  8. K15 Blazer Guy

    K15 Blazer Guy Member 2 Years 100 Posts

    i used 85-145 royal purple in mine, with the added capasity aluminum cover, so it tool almost 3qrt
    i dont think i even need to change it again lol
    i went super thick so it would coushion the gears and posi an much as posible for banging gears, towing, and offroading. cause this truck sees eveything given time
  9. steved

    steved Former Member

    I know some folks don't like Royal Purple (I for one only like their gear oil), but I had good luck with it in the last truck. The last truck took nearly eight quarts with an aluminum ORU cover...that was an 11.5" AAM though.
  10. Cowpie

    Cowpie Rockstar 3 Years 500 Posts

    Interesting. I have used synthetic 75w90 in the diffs of my semi trucks for over 2 decades with nary a problem. It is recommended by the manufacturers, who will bump up the warranty on those diffs to 750,000 miles if one uses synthetic 75w90. I kinda get the feeling it does just fine. If it can handle the work of a truck that grosses 80,000 lb, and runs 135,000 miles average a year, I am not sure why it would not work fine in a pickup. And that is only a class 1 or class 2 ride. A semi is a class 8. Took one of my semi's to 1.4 million miles with only replacing outside axle seals once in that time. No bearing or gear changes.

    And those semi diffs get Mobil 1 75w90 synthetic just like has been mentioned here. They came factory filled with it, and still use it.
    Last edited: Jun 3, 2013

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