Differential Gear Lube, SAE 140 or SAE 85w140?

[Brian Diehl]

I plan to change my differential oil before our summer trip.  I have let it go too long since the last oil change.  I have almost 40,000 miles on this oil and the book recommends 25,000.  The book recommends SAE 90 for temperatures below 0 and SAE 140 for temperatures above 0.  Is there any reason I should consider a multi-weight lube instead of just putting in the SAE 140?  I do drive the bus in the winter if it makes any difference.

Thanks for your ideas.

[DaveG]

85W140

[rv_safetyman]

Brian, you have a bit extra power going to that unit, so I would strongly recommend synthetic. 

I went with Shell Spirax 75W90 (http://www-static.shell.com/static/can-en/downloads/shell_for_businesses/oils_lubricants/1-28.pdf).  The pdf shows approvals from just about everybody.  When I had my rear end rebuilt, it was the recommended lube.

Jim

[DaveG]

If going Synthetic, remember to change your drain intervals. Basically in an RV application you may never need to change syn.

[Fredward]

Brian,
I would definitely go multi-vis. 140 is like clay at our average winter temperatures. I've heard many good things about synthetic. I just rebuilt my drop box and put multi vis 85-140 in; not synthetic. I've still got some leaks where the banjo is cracked so I didn't spend the money on syn.
Fred

[Brian Diehl]

A local distributor of the Shell gear lube told me he could get the spirax, but doesn't have it in stock.  He recommended Castrol Syngear synthetic 75w90 as a substitute.  Anyone with any experience such that I should avoid this?  Otherwise, this looks like what I'll get since he has it in stock and I can get it today.

[Brian Diehl]

Well, the Castrol Syngear synthetic 75w90 is now in the differential.  Not too bad of a job.  I did find a fair amount of metal particles (super small in size) attached to the magnet.  I guess that means my gears are wearing and going so long between changes certainly did not do them any good.  Hopefully this synthetic gear lube will help reduce the wear, reduce the temperature of the lube, and help the gears last longer.  

When was the last time you changed your gear lube?

[Fredward]

Brian,
Aren't you concerned about running 90 weight when MCI calls for 140? Or is the synthetic so good it lubricates like 140 wt at operating temperature? The Cummins is putting a lot more torque to that rear end than the Detroit did.
Fred

[RickB]

Brian,

Thanks for making me have my differential lube changed for peace of mind. I didn't go with synthetic though.

My bus A/C issues may be serious. Dan at C&J is checking it as we speak. possibly broken crankshaft or bad valves in the compressor That will not be a good thing, well it can't hurt to hope for a cheaper issue so i will until I hear otherwise from them.

I don't think we are gonna cross paths on your way to the west coast with Hilary and the girls so have a safe trip and give your girls a hug from the Barron family. We love you guys.

Rick

[JohnEd]

Brian,
Aren't you concerned about running 90 weight when MCI calls for 140? Or is the synthetic so good it lubricates like 140 wt at operating temperature? The Cummins is putting a lot more torque to that rear end than the Detroit did.
Fred

Fred's is a good point.  The 140 was called for because of the op temp and the effect that that has on viscosity.  Syn doesn't thin with temp (Sean, sit down) so 90 syn should be OK for "higher" temps and add to that that the syn doesn't contribute to the temp increase and I think you should be OK.  Given my vast knowledge of things slippery and engineering, well, that's worth little more than mental masterbation.  If you have increased the torque applied to the diff ten you are playing with fire.  Given that these things are "over engineered" and that the proof is in on that...I say you have an excellent chance of success.  Boost the torque beyond spec AND run a thinner oil and I think you are crowding your chance of success.  I would drain and save the 90 wt and put in the syn 140 cause 140 is whats called for with the lower torque input.   Save the 90 wt for someone with a normal setup.

BUT what does the oil rep say?  Will 90 wt syn sub for 140 wt Dino in the summer?  I want to know what you find out.

The metal particles, fine ones, are normal for "Amurcan Iron" stuff. 

[rv_safetyman]

JohnEd, if you look at the spec I posted a link to, you will note that virtually ALL OEMS and gear manufactures specifications plus some military specs (not always a strong indicator) are met by this lube.  

While we are locked in to oil specs for two-strokes that are pretty outdated (because of the nature of the two-stroke), I feel comfortable with updated technology on gears and bearings -- provided it meets OEM specifications.

Jim

[JohnEd]

Jim,

I don't fully agree with you.  I am certain you suffer no heartburn with that.

The OEM called for 90 wt in cold temps.  I also called out 140 for warmer ambients.  The syns track the petro oils by weight for application.  Ergo 90 wt can be substituted with 90 wt syn and 140 wt can be substituted with 140 syn.  Given that the diff in question is having more torque applied than what the OE engine put out AND that all the mechanicals are well worn......putting in syn 140 to replace the petro 140 seemed prudent.   A large advantage of the syn 140 is that it can operate at lower temps than petro 140.

I read your reference and I'll raise ya one http://www.shellusserver.com/products/pdf/SpiraxS.pdf

There is also a sheet specifically for Spirax 140 and it pretty much says it will work over the same temps as Spirax 90 so I can see no reason to go to 90 and a big one to go to 140.

Your comments about 2 strokes seem misplaced on this.? 

Respectively,

John

[luvrbus]

You guys need to read the oil specs on Cat Equipment every piece I owned  of the newer models in 20 years  used 10-30 in the winter below 0 and most of the time I used 30w for all the gear train and transmission,buses are nothing compaired to the torque they put on the ground I don't think the weight has anything to do with it.
JMHA it is the treatment process on the gears I don't believe synthetics or 140w will make any difference in these older buses when their time is up it is gone


good luck

[rv_safetyman]

JohnEd, I am sure that a heavier weight synthetic would work just fine.  The gear experts that rebuilt my rear end/drop box recommended the stuff I use.  I think synthetic can span a big spectrum.

I am out of my knowledge comfort level here, but I would bet that the 140 wt of dino oil was specified in order to get sufficient film strength under heavy loads and high temperatures in the "old" days.  Not a problem with either dino or synthetic today for brand names.

I was using the oil analogy trying to make the point that many of our buses are pretty old and "da book" reflects the technology of that era.  I think we can avail ourselves to modern technology without fear -- EXCEPT:  1) two stroke engine oil 2) technology that does not meet OEM specifications.  An example of the latter would be additives that are touted as being the latest in technology but are not approved by the OEM.

Once in a while, I go over the manual for my '46 Oliver tractor and laugh at the fuel and oil specs.  

Jim

[JohnEd]

Jim,

Agreed!  Especially that part about "me" being out of my depth...though you didn't say that about myself.  True though, none the less.