Differences in owners manual specs between 02 and 04 regarding diff oil?

852 Views 3 Replies 2 Participants Last post by  bigdaddyII
Looking at both the owners manual for my 02 1500 and my uncles 04 1500 there is a difference in the weight of gear oil that is specified. Both of these is 2wd trucks.

I have owned my 2002 for coming up on 60,000 miles, and am getting ready to do the 3rd go round of transmission filter and gear oil changes. The first change a few days after I bought the truck (110,000 miles) I used what the parts store was showing in there computer, which was 75w90 for the rear axle. Shortly after I became a member here and started reading that everyone was using 75w140 in the rear and 75w90 in the front axle, I then downloaded a 2003 service manual that specified 75w140 for the rear axle. On my 2nd change I bought and installed 75w140 figuring that the parts counter dud was just an idiot.

Somewhere in the past year my uncle bought an 04, and when we changed his and looked in his owners manual it specified 75w140. I didnt think anything of it and went on with the change on his.

With my 3rd axle oil change around the corner (170,000 miles), I began looking for my .75 quart of 75w140 Mobil 1 from my last change, which I now realize I gave to a guy at work whose pinion seal was leaking shortly after the last change. What I did find deep in the back of the laundry cabinet was .75 of a quart of Royal Purple 75w90 from the first change, and this got me thinking. I dusted off my own owners manual and arranged the pages back as best I could (the reason I didnt read it much to start with) and I found that the parts geek wasnt an idiot after all, my manual does indeed say that the truck rolled out of the Dodge plant with 75w90, and they really dont care what I use as long as its GL-5 rated.

Here are some shots from my 2002 manual:

My manual doesnt have a section with all the specs laid out for you, but rather lists them as it goes on telling you how to check certain fluids. I then found a site that offers you to read the 2004 manual in PDF format on there site and found that Dodge now specifies 75w140 in the rear axle of the 1500 trucks and 75w90 on the 2500/3500 trucks.

And this is the link:

My manual recommends fluid changes every 12,000 miles and the 04 manual every 15,000 miles. I was wondering if anyone knew the reason for the change in weights. Going from 75w90 to 75w140 seems a bit drastic to me to get 3,000 more miles out of the fluid. My wifes F150 uses 75w140 and Ford claims that is sealed for life (LMAO, nothing is, I change that every 50,000). When I did run the 75w90 for the first 30,000 miles, it drained out looking just as reddish/ purple as the day it went in, harldy spent. Obviously Im also interested in this from a cost standpoint as the lighter fluid can be had for almost half the cost of the 140. Any ideas/opinions/ridicules? Thanks for taking the time to read this long ass post.
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I just changed over to Royal Purple in my Trans & rear differential, it had 40,000 miles on it
then i went one step further & bought a differential cover with both a drain & fill threaded plugs, no more taking off the cover to change fluid. The drain plug is also magnetized, so it will grab metal shavings to let me know if i do need to pull the cover & do a better inspection.
If you do a lot of towing or off roading, use the heavier fluid, if you notice in your booklet with the 7 on the edge of the page, it reads FOR NORMAL SERVICE .... i couldn't tell what the next line is. There is usually Light, Normal, & Heavy duty service

To me Dodge goes overboard on service intervals, like my 2009 is the exact same engine as the 2012 5.7. My manual reads, change motor oil at every 3,000 miles, the 2011 reads 5,000 miles, the 2012 reads 8,000 miles. All lubricants are much better than the were 7 years ago & Dodge is finally admitting it.
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The "for normal service" sentence continued on the backside of the page where they went on to say that it doesnt need to be checked regularly unless a problem is being addressed.

I dont mind dumping the 75w90 back in there as I may tow or haul 1500 or less miles in the 30,000 miles it will be in there. I was just wondering if there might be a reason for the change of specification and the change in the service manual. If it has to do with Fords idea that it will never be checked or replaced then with my using the lighter fluid I wouldnt worry, even if I would be towing all the time because it will be drained at 30k. I know 30k is beyond the 12k that Dodge wants me to change it but dumping good gear oil every 12,000 miles is plain stupidity. If it is for any other reason though I would like to know before I put the lighter stuff in.

The confusing part for me is that the 75w140 is for the 1500 (light duty) trucks, but the 2500/3500 is listed for 75w90. I thought those were the trucks expected to be towing heavy. I know the rear end is different but that cant be the total reason.
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Okay, so I was able to do a little better search this morning and will post what I found in the rare event that some other soul may wonder and searches it here.

Apparently Dodge shipped these trucks out with 75w90 up until August of 2002. My truck was built in June 2002, so it came with the 75w90. Somewhere around August 2002, for whatever reason, they sent out letters to the dealerships and owners saying if any towing would be done 75w140 was to be used. They also started shipping out trucks with 75w140 already installed and spec'd all of the 9.25 rear axles at that from that point on.

I will be using Royal Purple 75w140 on my upcoming change as I still have half a bottle of it from the recent change in my wifes F150 and may experiment later with the 75w90 as I dont do much towing, and at 200k miles the diff may explode on its own anyhow. Thanks to the people who did take the time to read my thread, and to GTyankee who took a little extra time to at least throw a thought out there.
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