2004 Mercury Grand Marquis

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Oct 3, 2008
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25,000 miles on a severe service schedule with 80W-90. Motorcraft Premium Rear Axle Lubricant is a decent choice if you're going down that route. For more severe service, you can use Motorcraft Full Synthetic 75W-140 and take it up to 50,000+ miles easily. \:\!
 

crazyoildude

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what about factory fill what interval should i change that?? In the engine i use motorcraft 5w20 with a motorcraft filter in the transmission i use motorcraft atf flushed it did not change the filter yet, car has 30,000 babied miles what does everyone think? pure one air filter
 
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Illinois
 Originally Posted By: crazyoildude
what about factory fill what interval should i change that?? In the engine i use motorcraft 5w20 with a motorcraft filter in the transmission i use motorcraft atf flushed it did not change the filter yet, car has 30,000 babied miles what does everyone think? pure one air filter
Change it at 50,000 miles. I change my tranny every 45,000 miles M1 ATF. Engine oil every 10,000 miles. M1 oil.
 
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Feb 1, 2003
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RI
IMO, all gearbox oils should be changed out in 30k intervals. If you upgrade the sump capacity, then you can go longer. If it is a tough rear end in an under stressed application, then go longer. NJ drivers tend to be aggressive even if the the 'end in the GranMahkey is pretty strong. Even with chronic laziness and full synthetic, I would never go over 50k!
 
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Oct 26, 2005
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I dunno. We ran an '03 Marquis to 193,xxx and never changed the differential fluid (nor the transmission). Not intentionally. The youngest son got this car from me at about 90,000. I made him change out the rear-end and the transmission - or so I thought. The second deer strike took it out. He tells me (a month or so later) that he never did that service. RIP anyway.
 
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