Differential Fluid: Conflicting Information


sgtsandman

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Will 75w90 get me higher fuel mileage than 75w140? If so, how much better?
If there is a difference, it is so minimal that you won't notice.
 


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Ford went to 75w140 synthetic for the factory fill to improve fuel mileage due to reduced friction. It's not thicker than 80w90, when cold it thickens as if it was 75 weight and when hot it thins like it was 140 weight. The viscosity remains more consistent and is less affected by temperature, same as "multi weight" motor oil.
 

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Ford went to 75w140 synthetic for the factory fill to improve fuel mileage due to reduced friction. It's not thicker than 80w90, when cold it thickens as if it was 75 weight and when hot it thins like it was 140 weight. The viscosity remains more consistent and is less affected by temperature, same as "multi weight" motor oil.
My owners manual recommended 80w90 in the front and rear differentials. More recently, everyone was recommending 80w90 in the front and 75w140 in the rear. But I did 75w140 synthetic in the front and the rear. Is that ok? 07 Ranger with 4:10’s and rear LS.
 

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My owners manual recommended 80w90 in the front and rear differentials. More recently, everyone was recommending 80w90 in the front and 75w140 in the rear. But I did 75w140 synthetic in the front and the rear. Is that ok? 07 Ranger with 4:10’s and rear LS.
Based on my research no... And you are endangering mankind by doing so!

Physicist Edward Teller considered another possibility. The huge temperature of a fission explosion -- tens of millions of degrees -- could fuse together nuclei of light elements, such as hydrogen, a process that also releases energy (later, this insight would be the basis for hydrogen bombs). If the temperature of a detonation was high enough, nitrogen atoms in the atmosphere would fuse, releasing energy. Ignition of atmospheric nitrogen might cause hydrogen in the oceans to fuse. The Trinity experiment might inadvertently turn the entire planet into a chain-reaction fusion bomb.

Robert Oppenheimer, chief of the American atomic scientists, took Teller's suggestion seriously. He discussed it with Arthur Compton, another leading physicist. "This would be the ultimate catastrophe," wrote Compton. "Better to accept the slavery of the Nazis than run a chance of drawing the final curtain on mankind!"
 
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My owners manual recommended 80w90 in the front and rear differentials. More recently, everyone was recommending 80w90 in the front and 75w140 in the rear. But I did 75w140 synthetic in the front and the rear. Is that ok? 07 Ranger with 4:10’s and rear LS.
It will be fine. :icon_thumby:
 

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Gear ratios of 3.73 and more "should" use a 75-140 rated gear oil. Pinion speeds are up and more heat is generated so the higher "hot" viscosity is important. Mileage would not suffer enough to notice. Synthetics are also superior in higher heat situations. Mobil one is really a good gear oil. The only time I don't use a synthetic is with an Auburn differential. The "cone" style limited slips don't last as long with the "more slippery" synthetics. In my experience anyway.
Randy
 


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