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Comments on various Dodge/Cummins web-pages were all over the place when the subject of differential oils comes up. Anything from 75w-90 to 80w-140 were suggested for the Dana 80 regardless of Dodge's recommendations. Then I found this study which looks like it was at least sponsored by if not conducted by Amsoil: http://www.syntheticwarehouse.com/brochures/g2457_gearlube_study.pdf

If you scroll down on the chart to page 19 you'll see who the winner was (spoiler alert...it's Amsoil).

I've always stuck to an 80w-90 except when we were full time RV'ing. Looking at that chart I'm wondering if a 75w-90 full synthetic wouldn't work just as well if not better. Anyone?

 

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Don’t see why a synthetic 75w-90 wouldn’t work, as long as it have the limited slip addictive in it or you add it the truck should be fine. 
im running Lucas 85w-140 in my 1500 with a Dana 70/60 swap. Mostly cause I ordered the wrong fluid from summit, but it’s been fine for 4yrs now without issue. 
 

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I've had 75-110 amsoil in rear for 8 years now and 75-90 in front, probably need to change it soon, it has about 60k on it now and last time I checked it it looks exactly same and no metal on the magnet. 

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Yeah, I'm looking at the Mobil One 75w-90 LS (limited slip) for the next change. It came in second in this study but is half the price of Amsoil. 

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Posted (edited)

I'm so glad I changed mine on the 02 hundred thousand mile truck. The rear had obvious oil break down as it did not feel right when rubbed between your fingers,  felt like it had less lubricity and a pool of very fine grindings in the very bottom when running your finger down there. I cleaned all that out and used Dino 90wt. On the long trips that truck runs, making it easier to note any improvement, I noticed an improvement in mileage when I got back. I did the front also before leaving, wasn't as bad.

Edited by JAG1
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I'm coming up on 200K miles on the rig so the tranny and differential will get flushed. They usually get drained every 50K but since the mileage is going up I might start changing them out every 35K or so. The truck is set up with a fairly heavy Caravan Camper shell (all steel) and other gear that stay in the bed all the time. We're retired now and take off camping at the drop of a hat. Anyway, it's a modest load so I don't see a need for an 85w-140 differential oil. I think the 75w-90 will actually run cooler and using a synthetic it should hold up 'til the next change. That study I posted above has me leaning towards Mobil's 75w-90 syn. 

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I've never been a huge follower of oil studies. Typically the results go to the big brand names, AMSOil, RedLine, etc. 

 

There is other oil studies done here that people gone a long ways without big brand oil. Take to @cajflynn 1.3 Million miles and Never used any synthetic oils ever not to mention changed oil every 20k miles. Then there was @dorkweedthat ran over 84k miles on Walmart SuperTech Universal Diesel Oil 15w-40 and tested every 7k miles. Not to say the tested oils are bad but don't discount others. Seeing members running past 1 MILLION MILES mark and not using high dollar big brand oils is proof enough for me... Like @cajflynnjust Chevron Delo 15w-40 and Fleetguard filters nothing special. Like myself I'm either Chevron Delo or NAPA (Valvoline) for oil 15w-40 and NAPA filters right now.change interval of 10k typically. 

 

We've got another member here right at 950k miles now...

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 I agree with @Mopar1973Man, alot of the studies I have read are skewed to the manufacturer sponsoring the study. Also, alot of the store brand oils such as walmart for example are made by better known manufactures so the quality is there just not the name brand.

 I won't knock amsoil because I do use it in my harley, it did make a noticable difference there but that is an air cooled V-Twin which see some pretty warm temps in the summer. Completely different animal compared to our trucks.

 The biggest thing is consistent maintenance in the form of oil changes or at least testing the integrity of the oil and good filtration.

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Posted (edited)

IBMmobile's wife wishes he didn't have so many miles and was a well oiled machine. :2cents:

 

 

 

Edited by JAG1
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2 hours ago, JAG1 said:

IBMmobile's wife wishes he didn't have so many miles and was a well oiled machine. 

Ya. she wishes for a lot of things. 

251101357_animated-gifs-witches-201.gif.9f88c9fcf83fe7a71af90e97cb3a5810.gif  

 

I tow a lot so I change the diff oil every 30k miles; it's cheap insurance.  The FSM calls for 75w-140 synthetic when towing a lot.  At Walmart I garbed some Valvoline with limited slip additive.   I have an AC system evacuation pump and set it up with some hoses and a jar so I can suck the oil out of the fill hole.

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Posted (edited)
1 hour ago, IBMobile said:

 

I tow a lot so I change the diff oil every 30k miles; it's cheap insurance.  The FSM calls for 75w-140 synthetic when towing a lot.  At Walmart I garbed some Valvoline with limited slip additive.   I have an AC system evacuation pump and set it up with some hoses and a jar so I can suck the oil out of the fill hole.

I have a reversable oil pump and suction tube left from my old boating days. Thanks IBMobile for the idea as it will save having to redo the gasket ea. time.:thumb1:

 

I also used the Dino oil with limited slip additive but, had to add another 4 oz. to stop the chatter in when turning.

Edited by JAG1
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That study I posted was obviously sponsored by Amsoil. Still, the results were interesting in that the 75w-90's seem to out perform the 80w-90's regardless of brand. I'm going to give the 75w-90 synthetic a try this fill. No way to know what's going on inside the differential without a temp probe but it's hard to believe a synthetic would perform worse than a dino oil.

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Posted (edited)

I use 75w-90 Amsoil in my 4Runner and truck. The 05 was changed at 50K mile intervals and always looked new. The 18 will get changed a little more often until the warranty is up, then likely the same. 
 

The 4Runner was changed at 30K, then at 100K, and just recently at 200K (all odo readings, not intervals) and the used Amsoil lube is always in great shape. The lube with 100K miles on it felt like new lube. 
 

The factory fill on my 18 was toast after 15K miles, despite the 20K mile service life. So if you ask me the brand of synthetic does make a huge difference and it’s often with a few extra bucks, especially when you can reduce the services too. 
 

I need to do all the fluids in my Jeep and will be using Amsoil 80w-90 only over the 75w-90 because it’s cheaper and the Jeep only gets a few thousand miles a year and doesn’t tow anything. I’ll never have to change it again unless it gets contaminated. 

Edited by AH64ID
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I just ordered some 75-90 for the front and 75-110 for the rear from amsoil. $20 for preferred customer gets you a good discount and order over $100 is free shipping. I also put on a magtech cover in the rear that holds like 8qts. I probably have 50 or so thousand miles on it (make it like 80 :think: ) , not sure how many years but I know it's over 6 and it still looks new. ((( I just went out and looked when I got the mag cover.... It was in 2010 :thud: man time flies, this means I had it on for like 10 years with same oil )))  I've checked the temps with rf gun before and after I put mag cover on and I clearly remember improvement just don't remember actual temperatures. Last few years I haven't really towed anything but my boat. I debated on putting stock cover on to save on fluid but $60 whatever bucks every 6 years (10 lol) is not a huge deal considering oil now still looks good. I check the dipstick once a year and never had more then a dusting on it. 

Used amsoil in the engine too for few years but then switched to cen-pe-co that's made few hours from me and most Farmers use it in their equipment and sled pulling with good results, it's a parafine based and supposed to be great at high loads. Did few oil analysis and it's as good as amsoil. Where does time go? these gremlins I tell you...

()= Inserted after I realized how long it's been.

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