questions about differental fluids

Joined
Jul 25, 2009
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Location
ohio
i have a 2005 pontiac gto 24000 miles , the manual calls for 75w-140 diff oil. i called friday to see if my pontiac dealer had the friction modifier 7098 to add to the fluid. he said that three months ago gm changed the fluid to 75w-90 and that the friction modifier was no longer avaible to purchase. he said the new oil came mixed with the friction modifier in the bottle. i called a chevy dealer and have been told the same thing. i don't know alot about oil so that is why i am here. now the questions why would they change the oil from 75w-140 to 75w-90 ? and should i continue to use 75w-140 ? can i purchase the friction modifier 7098 some where else ? thanks for any help tim
 
Joined
Nov 17, 2002
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Don't know why they changed but 75W-140 is not typical viscosity gear lube for any GM cars. Now the GTO is not anything different than the CTS-V or the Corvette yet they ues 75W-90. 75W-140 is used mostly in HD trucks like those with dual rear wheels etc. Why the GTO calls for that I cannot say, maybe an over sight since the car was produced South of the Equator and the climate is considerable warmed than NA. I know AMSOIL has a friction modifier for this purpose.
 
Joined
Dec 28, 2003
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Manitowoc, Wisconsin
The GTO diff is a pretty finicky piece and can be a noisy S O B. I have had good luck with people running Amsoil Severe Gear 75w-140 with the "GM" friction modifier added to it. The Torco RGO 85w-140 petroleum or Torco SGO 75w-140 synthetic gear oil with the Torco Type F modifier in either of those is also a GREAT choice.
 

torridredgto

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Jul 25, 2009
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ohio
sorry for posting in the wrong place . can this post be moved . i am new to the computer age. sorry again.tim
 
Joined
Oct 3, 2008
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Kuwait
Could be a North American market thing. shrug Over here, the same vehicle is sold as the Chevrolet Lumina SS Coupe, and calls for 140 weight. Any Australian Monaro owners on the board?
 
Joined
Aug 19, 2009
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112
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Canada
It really doesn't matter that much. Hotter climates will spec a thinker fluid as the axel will run hotter. The 75w-90 will run a bit cooler and give a bit better fuel economy. The 140 will protect a bit better under heavy loads/performance driving...
 
Joined
May 1, 2003
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The GTO comes to us in the USA VIA HOlden Australia operations. THey run thicker oils period in the land of OZ. Since CAFE does not exhist and all of OZ is about like living in Georgia or ALabahama in that it is always hot enough out to run what you like. Even if it get colds during winter it is 80 degree's F out by lunch time.....THat is why it spec.ed 140wt gear oil....Different marketing department! Thier is no reason not to run 75W90 in it unless you just want to run a 140wt. If you decide to run a 140Wt. make sure itis a good one because the cheap ones have problems operating when cold out. I like Redline Gear Oils as my 1st choice. You should not need to add any friction modifers if you go with the right product as most have LS additives built in. Redline makes a 75W250 that is great for applications that are picky and noisey. Personely though I would go with a 75W90 and call it a day. I have not used Amsoil new 110Wt gear oil so it is anyones guess how it will work. I think Redline makes the best gear oils on the planet that are readily avaialble and have a long history of being race proven and street proven. Most companies do not have products that do both well. Redlines Shock Proof gear oil is about as good as it gets.
 
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