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New Dodge owner here. I have run Synthetic oil in the rear end in other trucks to help squeeze another mile or two out of the gas tank and I wanted to know what your experiences and suggestions were.

Also, does anyone have a listing of Dodge axel codes? I have an '01 w/318 and towing package. The sticker says Corporate 9" rear end. Is this the 3.92?

Mac
 

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I have used Synthetic in several other vehicles. I am planning on changing over this one as well.

As far as the axle, mine is a corporate 9" with the 3.55 gear ratio...so it could be either.

Jim
 

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Screaminhelo said:
New Dodge owner here. I have run Synthetic oil in the rear end in other trucks to help squeeze another mile or two out of the gas tank and I wanted to know what your experiences and suggestions were.

Also, does anyone have a listing of Dodge axel codes? I have an '01 w/318 and towing package. The sticker says Corporate 9" rear end. Is this the 3.92?

Mac
I run 75W90 Amsoil synthetic in my diffs. Haven't had a problem since. I did notice an ever so slight mpg gain after I changed the engine oil over to synthetic as well. I replace the diff fluids every 60 000kms just to clean the pumpkin out and check the magnet. Amsoil states that I can double my drain interval but I take the stock interval (40K or two years) and add 1/3 onto that. That's extended enough for me. My D rarely travels above 62mph, which helps with the wear and tear factor. To find your axle ratio check for a sticker in the glove box with it posted, or along the side of the door. To verify you have the 9.25" rear axle, it will have 12 bolts on the cover. The 8.25 has 10.
 

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Hey, thanks for the quick replies! I am really thinking about Amsoil. I don't know much about RP but that is still a possibility. I am thinking about synthetic in the crankcase. Since this thing still isn't leaking after 126k, I may go ahead and do it. I realize that I can't get blood out of a turnip (it is a truck after all) but I hope to make the gas pump a little less painful.

I will check the rear end and the stickers today. I am guessing that it is a 3.92 by the way it drives. The truck is strong between 1500 and 2k. That is partially thanks to the Flowmaster that was on it when I got it but it feels much stronger than a 3.55.

Mac
 

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If you cannot find any stickers with the axle ratio on them, send your VIN into the dealer and they'll be able to tell you everything about the truck, including which axle ratio you have. An easy way to tell which rear end you have is highway rpm, as the transmission ratios for the 5.2 and 5.9 are the same: Providing you have 31" tires; at 60mph a 3.55 ratio will drive at 1600rpm and 1800at 65mph. A 3.92 will turn over at close to 1800rpm at 60mph and 2000 at 65mph. If you find that you have a few minutes to play around check this out: www.biodsl.com/rpmcalc2.xls , you'll need Excel to open the file. I have it set up for my R/T specs (30" tire and 3.92 rear axle) but change it around to your specs and it will give you a generalization of your rpm at any given speed. Enjoy.
 
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