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Discussion Starter #1
I just swaped the stock diff covers over to Mag-Hytech diff covers for better cooling, and higher gearoil capacity not to mention I think they look neat. I'm taking my travel trailer on a 2500 mile trip next month. Whats the best diff fluid weight for heavy towing? My owners man says 75w90 but I just wanted some other input.
 

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Most guys as well as myself run Amsoil. I run 75-140 in the rear and 75-110 in the front. 110 is really fine for the rear too, but I tow tons so its just a little added protection..
 

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Nick N is right. 75W90 gear lubes are being passed up for the better protection of the new API spec 75W110. And as Nick N said, if you tow heavy a lot, a 75W140 is going to give the best protection.

-Chuck
 

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I run 75w-90 front and rear. I also ran the same in the AAM axle in my old GM 2500HD.

I have almost 100k combined between the trucks with lots of towing up to 11,000lbs. The gears always look good and the oil comes out looking good as well.

The 75w-90 seems to be working great for my application.
 

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Discussion Starter #5
the 75w140 is that ok to use in cold climates? I live in Arizona right now, but will be moving to Michigan in May.
 

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Yep...handles the cold no problem...
 

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Discussion Starter #7
About how many quarts does the rear diff hold? I just checked the owners man and nothing is said about the amount, only the proper weight. I don't want to come up short on how many quarts to buy and not have enough.
 

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Discussion Starter #9
holly cow thats a great site worth of info. Thank you very much
 

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I read here on the forum that if you run the oil level too high it can affect the durability of the seals. I was very surprised to find out that they recommend filling the rear diff to an inch from the bottom of the fill hole. I am not sure if this applies to both the front and rear diff. So you should find out the proper height from some one so that you know how much oil to put in with your new covers. I want to install some of those cool Mag covers one day also!
 

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I'm ready to do mine too at 15k like the book says. Will using the 75w140 void the warranty?
 

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The rear fluid capacity with the Mag-Hytec cover for 3500's is 8 quarts,but use the dipstick on the cover and check.Mine was full at 7 and 1/2 quarts.I tow heavy and run Amsoil 75w90.The added protection of Amsoil and the extra capacity and cooling of the Mag-Hytec cover will be just fine!!
 

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The rear fluid capacity with the Mag-Hytec cover for 3500's is 8 quarts,but use the dipstick on the cover and check.Mine was full at 7 and 1/2 quarts.I tow heavy and run Amsoil 75w90.The added protection of Amsoil and the extra capacity and cooling of the Mag-Hytec cover will be just fine!!
X2 on the fill marks. I run 140 and have 60,000 miles on that fluid. I checked it the other day and the oil is still see thru. Just has a darker tint. Im guessin this will be good to 100,000 miles
 
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