Somebody please tell me why exactly I am supposed to change the diff oil every 15K. I use Mobil 1 synthetic 75w 140 and it gets real expensive to change. I do what my owners manual tells me to, but I feel like I am wasting perfectly good oil. It looks clean and I know it will last a hell of a long longer than 15K before breaking down. No other vehicle I've ever had recommended changing diff fluid this often. What gives? Why is this differential unique?

THis is on an 06 2500 4x4.

 

Keep changing your diff oil until it starts coming out clean, then extend the change interval.

I am running 75-140 synthetic Valvoline in mine. I just changed it last week with 50,000 miles since the last change. I now have over 150,000 miles on the truck. The oil was so clean I could not tell it from the new stuff and the magnet had so little material on it that I had to wipe it on a rag before I could see that there was some steel there.

There is no need to change it more than that once it is broken in. Probably 100,000 miles would be fine as long as you don't work it too hard or submerge it. My driving is a mix of light to medium loads on the highway and towing in the mountains.

Now with the Dynatrac kit in the front end, I'm in no hurry to change it either.

 

i tow heavy so i change mine about 45k

 

i've changed mine twice in 200,000 miles

 

And the sad part is your proud of it!

 

It's the old "the good book says so" argument. I've never been one to go strictly by the book.

In the semi trucks I've owned I would change the fluid every 500,000 miles. Granted, it's a different animal, but the principle is the same. I was pulling 120,000 lbs with the last truck and the oil was as clean as the day the factory installed it. Were the wear additives still functional? I don't know, that's why I changed it.

I changed my rear fluid at 40,000 miles and doubt I'll do it again until 140,000. I see it as a waste to change it every 15,000 miles. A waste of my money and a waste of natural resources. Don't get me wrong, I'm no tree hugger, but I do burn my used oil in a waste oil heater rather than dump it in the gravel driveway as dust control.

I even went as far as replacing my antifreeze with something that would shock most of the bookers here, non-hoat antifreeze. I know, I know, my engine will probably self destruct in 10 or 15 miles. But hay, it's my truck and my money. Just because some legal eagle pencil pusher says to do something or else, doesn't mean I'm going to jump up and do it. After all, I wonder how many trucks are sitting at the junkyard pushing 300,000 miles, engine and body long since used up with the original gear oil still in the rear end?

 

My father bought a 68 roadrunner and drove it evry day for 36 years he changed that rear end fluid after 29 years and the posi still locked up and the rear end never made a not 1 sound, I cant imagein our rears destroying oil in 15,000

 

I think my book the 15k interval is only listed in the towing/short trips service schedule.

IMHO, I'd do the 15 k service while under warranty, then run longer...

 

recently changed the fluid in both diffs at 43K miles. the oil looked like new and didn't have any sludge or any metal on the magnectic fill plug.
i don't tow heavy but have driven long interstate miles with it. this truck does not see off road use neither.
probably could have waited till 100K miles

 

I used Mobil 1 75/140 rear and 75/90 front for the last change at 50K. The factory oil was still very clean. I can probably change it at 50K intervals with no ill effects. I pull fairly heavy with the truck and have no issues. Mobil 1 is a very high quality oil and as long as it does not get contaminated, I can't see it wearing out that fast. Scotty

 

Yeah, I run Redline, which I feel is also a high quality synthetic...

Both this truck and the last one had a bit of metal muck, so I guess doing the first change at 15k if you tow heavy wouldn't be too bad of an idea, plus then there'd be no questions if you had a warranty issue.

 

I spoke to a AAM engineer a few years ago.It was AAM whom recommended the 15k diff service under severe usage.The engineer also said they were the reason for the reusable gasket.It was to enhance the ease of differential service. He also said the 15k service interval was for longevity.Also that rear axle is designed for the 75w90 not 75w140.The smaller corporate axle is 75w140. Way back when Nissan and Toyota for years suggested every 15k also in normal use and not just in their trucks but in their whole lineup of rear wheel drive and four wheel drive vehicles.

 

Gaurdrail- I like your take on things...keep in nice and mellow, this is a truck, it will survive.

I think that the 75w90 is what's recommended but if your towing and in hot weather it can get a bit 'runny' so to say and the 75w140 works better, less slip, etc.

the folks I've talked to who work in gear shops all have said go with the140

Question...is it wrong to run 90w in the front and 140w in the rear??...I would think whatever you go with (either one being acceptable) just do the same front and rear.

 

AAM says 75w90.Both my 98 1500 and my 06 Gran Marquis says 75w140.But NOT my 03 3500.Must be something to it.Until I see PROOF in writing or in testing or running temps towing etc.I'll stick with the 75w90.

 

Sounds like most of you agree with me that a change evey 15K is wasteful. Still not sure why the manual says to change it so often. Makes no sense at all to me.