Ford - Be Consistent!!

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Nov 24, 2003
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I have a 2006 Mustang GT. Why does the V8 engine specify 5W20 yet the old-style 8.5" rear end specify 80W140 (not 75W90). I would argue that the rear gear has just as much potentual, or even more, to gain mileage with a lighter oil. Ford knows that the rear gear needs the heavier oil to be reliable (they've fixed alot using 75W90)- wonder if they also know that for the engine?
 
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Old style rear ends had hypoid gears, which are very tough on lubes. There is some sliding that takes place between the ring and pinion gears, at extreme pressure angles. Nothing in an engine, or even a modern transaxle [helical gears], is as tough on oil as hypoid gearing. too crazy - Great point - Ford is bordering on hypocricy.
 
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My 1998 GT specifies 80W-90 in the rear end. It is the 8.8" rear end. I need to change it soon and I plan to use Mobil 1 75W-90 in it. I run Mobil 1 EP 5W-30 in my engine.
 
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I guess they figure the need a stronger oil since the V6 owners whould have wished for a V8 and drive the crap out of them to stay up with a V8.
 
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The 4.0L V6 is a derivative of the German Cologne V6 designed more than 3 decades ago. Old German design = thicker oil, quite often.
 
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