Engine/Transmission (1998.5 - 2002) 75w90 or 85w140 in rear diff?

[storm'in]

Hey guys, was wondering if I should use 75w90 or 85w140 in the rear diff. I will go full synthetic. Manual says if you tow, use 85w140 synthetic. But I don't tow heavy. 5% of the miles I tow between 3-6K lbs. I done some searches and 85w140 seems like it may be overkill. Some say it affects mileage too. TIA- for any advise and/or suggestions.

-Dave

 

[HEMI®Dart]

storm'in,



From what I have read if you use a high quality Synthetic gear lube, 75w90 is plenty heavy enough.



I agree 85w140 is probably overkill. If you were towing a 20,000 lb trailer through the rockies in 90° heat, it might be justified.

 

[rblomquist]

Agree with above post although there's something to be said for overkill, I mean you do own a CTD even though don't tow heavy right Get some high quality 75-90 and you should be good. I live in a furnace part of the year and tow something almost every weekend i. e. boat, or RV



Just changed mine out today with Amsoil 75-140. Man the mag-hytec cover is nice for that procedure!

 

[C Schomer]

75w90 (even the best syns) sure didn't cut it for me in Denver and the mtns. and I don't tow heavy but I run hard. 75w140 syn (like my manual calls for) did good. Now I use 85w140 in the desert. Craig

 

[Gary - K7GLD]

Any "fuel mileage sacrifice" with the heavier weight oil would be trivial if even measurable - but the added protection MIGHT prove critical over the long haul. I use Valvoline semi-synthetic 85/140 in my LSD, towing a GCW of about 15,000 lbes - fuel mileage is just fine, and I have NO concerns as to lube efficiency in the differential - what will you REALLY "save" with the lighter stuff?

 

[DTullis]

Gary



Valvoline DuraBlend 85W-140 is what I was planning to put in my LSD. Valvoline claims it is for limited slip and conventional Diffs.



I was wondering if you had to add any friction modifiers with the DuraBlend?



I believe that I prefer the blend to the synthetic. That way I can afford to change it every 15K or so when towing.

 

[Cooker]

IMHO a quality 75w90 will be plenty good. FWIW - I have heard from a few different sources that an increasing number of the OTR trucks are running 75w90 and they are towing well in excess of what you will be towing with your Cummins.

 

[Gary - K7GLD]

Don, I went to the Valvoline after trying a popular full synthetic, and my limited slip function immediately ceased to function - so I drained that and then went to the Valvoline - it is used straight from the bottle, *my* LS works perfectly, and no friction modifier was required - YMMV!



COOKER -



Sure, you CAN get by with the lighter stuff most likely, but with no real difference in cost, and potentially less protection, what's the point?



My RVing bud thought HE could "get by" with the lighter stuff too, but with 75,000 miles on his truck and a $1200 bill for a differential rebuild, he sorta figures differently now...

 

[cumminspwr01]

The Eaton and Rockwell manufactures both run 75W90 synthetic in there drive axles. If its not in there it voids the warranty. I was wondering if it would make a difference the fact that these axles also hold two to three times the capacity of the danas. I also run the 75W90 synthetic but I never haul anything and the weather here in Pa isnt very harsh one way or the other but Cooker is right about the otr trucks

 

[Gary - K7GLD]

OTR truckers ALSO trade in their rigs at pretty low mileage - and pass any problems on to the NEXT owner...

 

[Cooker]

Originally posted by Gary - KJ6Q

OTR truckers ALSO trade in their rigs at pretty low mileage - and pass any problems on to the NEXT owner...

Maybe that is the case in your part of the country but not around here.



I know several owners, operators, and brokers in the OTR trucking industry and I guess if you think 400k-600k miles is low mileage then that would be a true statement. The company my GF works for runs their trucks to 750k-800k before unloading them.





Also interesting to note is a 75w90 will run at cooler temps than an 75w140 or an 85w140. Although I don't feel heat is an issue when discussing damage to these differentials.

 

[cumminspwr01]

The otr drivers around here dont do that too much either. They are usually the ones buying the used trucks. The ones who use the trucks until the warranty is up and then dump them are the bigger fleets. I guess if you can afford it then thats the way to do it. Several trucks come through here with well over 1million+ miles on them running 75w90 synthetic in the rears and to the same extent we have a lot of trucks have the rears fail running the same fluid. They dont usually fail because of the lube its usually driver error or lack of maintenance.

 

[rblomquist]

Comparing big rigs with our application is not apples-to-apples though. Yes, we're talking about gears but it's faulty logic to talk about each in the same breath. Every vendor engineers/designs a product to work with specific parts (including lubrication). So if OTR guys are using 80w (or whatever) in their Eatons that's fine if Eaton designed the gears to work with that oil in a given service mode.



I just boil it down to the manufacturer level: DC/Dana call for heavier oil in the differential if you tow. Now, if you don't tow heavy you can stay with the factory fill of the lighter oil or if you just choose to stay with a lighter oil while towing heavy, and go against what the company that designed/built the product calls for you can do that too.

 

[Gary - K7GLD]

A Ham acquaintance of mine drove for Swift - and told me they traded their trucks in at 500,000 miles - pretty low mileage for that type of rig. But as you say, owners lower in the food chain can't afford that luxury.



BUT, the differentials in those rigs are in a different class than ours too...

 

[cumminspwr01]

yeah they hold up to three times the capacity

 

[cumminspwr01]

I misinterpreted (I think thats right) what you said the first time. When you said otr truckers I thought you meant owner/operators but yes almost all fleets like swift, schneider, crete and any of the others usually trade their trucks off at almost exactly when there warranties run out.

 

[Cooker]

Originally posted by rblomquist

Comparing big rigs with our application is not apples-to-apples though. Yes, we're talking about gears but it's faulty logic to talk about each in the same breath.

True. The OTR trucks are typically operated at a steady state in pretty clean environment. They are not subject to the contamination our trucks, especially 4x4's, are subject to and they are less likely to have issues with condensation than our trucks. Niether of these two issues have anything to do with the viscosity of the oil but rather the change interval.



Other than the differential having more capacity, I do not see how there is a great deal of discrepancy in how the differentials function. Granted I have never taken apart an OTR diff but I assume they are lubed by "splash" lubrication like out Dana's?



I think the issue when discussing gear oil and the protection it offers while under pressure (the ring gear pressing up against the pinion. Granted in an OTR truck there is more surface area between the mating surfaces of the ring gear and pinion but I don't know that these surfaces are under less PSI of pressure. Our truck may gross at 30k while and OTR truck may gross at 180k. True a 75w140 will be less likely to shear out under the pressures, but if a 75w90 is working well in an OTR application I do not see a reason that it would not be adequate in our Dana's?



Maybe I do not have a complex enough understand of OTR differentials to make sense of this?

 

[JJW_ND]

Call Dana Axle CO.

I did back when my truck as new and they told me the only place they would recomend the 140 weight oil (syntheitic or not) was southern climates (Like TX) and even then if the the truck was pulled at its max GVWR. Otherwise 75W90 was all they said was neccessary.



I have ran 75w90 for over 240K miles. Hotshotted trailers from KS to ND the first 200K miles. Many loads well over GVWR or so long (wind drag) that it was WOT for most returns. Plenty of trips in 90 - 100 degree heat. Changed rear diff. ever 40 - 50K miles. Every change sampled. Other then the pinion seal, the read diff. in my truck is total factory original. It has LSD and is as tight as the day I bought.



Maybe something has changed since 1996-7.



Please keep in mind a change to any good synthetic does not mean a fill of life. When I was pulling hard the 40K interval was about the limit or TAN (acids) were getting to high.



Based on my experience, I find it hard to believe damage that occurred from using any good full synthetic 75W90 would have been prevented by using 85W140. I think there is more to the story. Premature failure that no oil could have prevented? Pushed the change interval?



Run what makes you happy but don't think 75W90 equates to Rotella and 85W140 equates to Mobil Delvac 1 Full synthetic.



jjw

ND

 

[GFrance]

Originally posted by Gary - KJ6Q

OTR truckers ALSO trade in their rigs at pretty low mileage - and pass any problems on to the NEXT owner...

Well I had my last truck 15yrs 1,400,000 miles before it got replaced. Went thru one front & one rear differential. thats pulling 105,500lbs of truck & trailer 11,000 gal. of fuel. Always used 75/90 synthetic. New truck 2000 & will go until I retire in 2014 pulling the same weight up & down the mountains of Oregon.

My Dodge I use Amsoil 75/90 syn & pull my 12,000lb 5vr.

 

[storm'in]

That's some good info. - thanks guys. I installed my M-H cover last night w/ Royal Purple 75w90 full syn gear oil. It seems that it's what the majority of you guys are doing that don't tow MGVW.

The quality of the M-H cover is very high- and it should be for the price! One thing I noticed is the cover looks like it might hit the spare tire. I loosened the tire and pulled it back as far as I could and it still looks like its going to hit. I have 265/75/16s. Anybody else had this problem? Ive read of this problem w/ the Dana 80, but not the 70.









JJW, does your truck have a Dana 70 rr end? That post does it for me.