10w oil for Unimog transmission

[frenchian]

Hi all,
I'm new on here, so excuse me if this has already been raised (I haven't found it though)

I have a 1986 ex-military Unimog and want to change all fluids before heading off into Africa with it.

Most fluids are (relatively) easy to identify - but the manual transmission spec from Mercedes shows that the military gearboxes use 10w engine oil to MB spec 226-227.1. No-one seems to know anything about this old spec - in fact the only straight 10w engine oils I can find in UK currently are Shell Rimula R3 (http://www.oilsandstuff.com/sites/default/files/Rimula R3 10w TDS.pdf) and Fuchs TITAN TXE 10 (http://www.opieoils.co.uk/p-68967-fuchs-titan-txe-10-monograde-engine-oil.aspx).

As we're going to be totally dependant on the truck for a year I want to make sure that I get the best-suited oil possible and would be keen to know if anyone has any advice as to the suitability of these two oils (or of any other oil you may know about that could be better suited?).

Thanks, Ian

 

[user52165]

Welcome newbie. I don't know the answer but I am certainly interested in your adventure. If possible, keep us informed on your travels and the condition of the Unimog. That "totally dependent" term really hits home.

Someone with good info will surely chime in. Did you contact MB?

 

[Pablo]

You want something like this:

Amsoil Power Shift 10W

If the tranny is well broken and it's going to be burning hot, consider the synthetic 30W version as well.

 

[2oldtommy]

I would be inclined to find a suitable synthetic gear oil compatible with this transmission. First question: does the gear oil lubricate ONLY rotating gears? If so, I would look for A light weight synthetic 75w-80 GL4. If a combination wet clutch is involved, stick with a suitable HDEO. Certainly a call to MB would answer your questions. FWIW--Oldtommy-- And welcome to BITOG!

 

[frenchian]

Interestingly MB have been decidedly unhelpful on this - they pass me onto their "Unimog Center" who it turns out are not interested in supporting vehicles, just selling them.

The gearbox is separate from the motor/clutch, so the oil is only lubricating rotating parts.

The civilian versions (with a slightly different gearbox) use 80 to 90w oil and there are many reports of people using GL4 oils in them - is there a big difference in properties between a straight 10w and a 75w-80? (the numbers seem to suggest so - but maybe not?)

 

[m37charlie]

I know this has been hashed thru on the benzworld site already.
Certainly you can't get Amsoil products in the UK very easily, and not at all in Africa.
I'd recommend a synthetic 75W85, which in the UK boils down to Castrol Syntrans.
I used Mobil Delvac Synthetic Trans. Fluid 50 (a fairly heavy 75W90 GL4) on my trip to Australia with no problems whatsoever.
It should last the whole trip unless you have leaks.
Whatever you do use a GL4, not a GL5.

Charlie

 

[user52165]

Did you try this forum:

http://www.benzworld.org/forums/unimog/

Curious what model you have and tell us something about it. I have seen one in my town. Very rare here.

 

[Shannow]

Every now and then a kitted out Mog comes through town, and I'm drooling...military ones about twice as often, but people lucky enough to have one...congrats.

When I'm looking for ideas, I usually go to "mobil.com.au" for their product recommendations.

This is what comes up for the U1000, 1200, 1250
Quote:
MERCEDES-BENZ [Unimog Models]
U1000, U1200, U1250

Crankcase - OM 352/ OM 352A N/Asp./ Turbo Engs.
MOBIL DELVAC MX 15W-40
Service Refill Capacity: 14.5* Litres
Transmission
Refer MOBIL DISTRIBUTOR
Service Refill Capacity: 10.5-13 Litres (see notes 239, 4)
Hydraulic Res.
MOBIL HYDRAULIC OIL 10W
Service Refill Capacity: 31 Litres
Differential(s) - Axle Differentials
MOBIL DELVAC SYNTHETIC GEAR OIL 75W-90
or MOBILUBE S 80W-90
or MOBILUBE HD PLUS 80W-90
Service Refill Capacity: 2.5 Litres
Final Drives - Hub Reductions
MOBIL DELVAC SYNTHETIC GEAR OIL 75W-90
or MOBILUBE S 80W-90
or MOBILUBE HD PLUS 80W-90
Service Refill Capacity: 0.25 Litres each
Other - PTO Gearbox
MOBIL AGRI SUPER
or MOBILFLUID 424
Service Refill Capacity: 5.7, 8.0 Litres
Power Steering - Power Steering
MOBIL HYDRAULIC OIL 10W
Service Refill Capacity: 2.25 Litres
NOTES
*
Includes Oil Filter
4
Transmission housing.
239
Castrol Syntrans 75W/85 or equivalent synthetic gear lubricant meeting Mercedes-Benz Sheet No. 235.4 is recommended


and 1300, 1700

Quote:
MERCEDES-BENZ [Unimog Models]
U1300, U1700

Crankcase - OM 352/ OM 352A N/Asp./ Turbo Engs.
MOBIL DELVAC MX 15W-40
Service Refill Capacity: 14.5*, 15* Litres
Transmission
Refer MOBIL DISTRIBUTOR
Service Refill Capacity: 10.5-13 Litres (see notes 239, 4)
Hydraulic Res.
MOBIL HYDRAULIC OIL 10W
Service Refill Capacity: 31 Litres
Differential(s) - Axle Differentials
MOBIL DELVAC SYNTHETIC GEAR OIL 75W-90
or MOBILUBE S 80W-90
or MOBILUBE HD PLUS 80W-90
Service Refill Capacity: 2.5 Litres each
Final Drives - Hub Reductions
MOBIL DELVAC SYNTHETIC GEAR OIL 75W-90
or MOBILUBE S 80W-90
or MOBILUBE HD PLUS 80W-90
Service Refill Capacity: 0.25, 0.6 Litres ea.
Other - PTO Gearbox
MOBIL AGRI SUPER
or MOBILFLUID 424
Service Refill Capacity: 5.75, 8 Litres
Power Steering - Power Steering
MOBIL HYDRAULIC OIL 10W
Service Refill Capacity: 2.25, 3.25 Litres
NOTES
*
Includes Oil Filter
4
Transmission housing.
239
Castrol Syntrans 75W/85 or equivalent synthetic gear lubricant meeting Mercedes-Benz Sheet No. 235.4 is recommended


I think Mobil telling you to go to Castrol carries some significance.

 

[frenchian]

What I'm currently trying to do is to work out what the differences between the MB recommended (10w) oil and 75w85 are. Looking at the viscosity charts they are different beasts.
MB must have recommended 10w to the military for a good reason(?). It seems that no-one knows what the old MB specs refer to (226-227.1).

Charlie - you've used a 75w90 - I assume from your vehicle that this was in a civilian gearbox - ie you were running what MB recommended?

 

[ledslinger]

I don't know the exact details but here is a possibility of what you are dealing with. Inboard marine transmissions in civilian versions spec ATF, but military applications use motor oil. The military spec is to allow a more universal fluid, one that will work, but not as well as a more specialized fluid such as ATF. This is likely intended to simplify logistics and field service.

Especially since you are having difficulty learning about the military spec, I would assume the fluid spec could be to simplify service, rather than providing the best lube. Lean toward the closest civilian spec fluid.

 

[m37charlie]

Originally Posted By: frenchian
What I'm currently trying to do is to work out what the differences between the MB recommended (10w) oil and 75w85 are. Looking at the viscosity charts they are different beasts.
MB must have recommended 10w to the military for a good reason(?). It seems that no-one knows what the old MB specs refer to (226-227.1).

Charlie - you've used a 75w90 - I assume from your vehicle that this was in a civilian gearbox - ie you were running what MB recommended?


Mercedes recommends
http://bevo.mercedes-benz.com/bevolisten/bevo-sheets-sort1.html
sheet 231.3, page 1
75W85 for basically all Unimogs except the BW 435s, where 10W is recommended.
However, in my North America U500 Owner's Manual, the Delvac Synthetic Trans. Fluid 50 is recommended, likely because Syntrans is hard to find. That's a 100C viscosity range from 11.8 to 17.5. 40C range from 64 to 132! And it works fine, although it would get thicker at -25F to -30F. I think something like Syntrans would be better in my climate, though I'm going to run the 50 next winter as an experiment.
Being in the UK, Castrol Syntrans should be easy to find and I sincerely doubt it would actually damage the 435 gearbox. Going to Africa, it is better to err on the thick side than the thin side.
I would try it and see how it is on the infamous 4 to 5 upshift.

Charlie

 

[m37charlie]

I draw 3 conclusions re Unimog 8 spd gearboxes:
1) They are relatively forgiving as far as viscosity choices
2) Going a step or 2 heavier in a hot climate is OK
3) Synthetic is better as long as GL4, not GL5;

but 75W85 is closer to 10W than 75W90!

Charlie

 

[Doug Hillary]

Hi,
m37charlie - Best wishes to you both. I agree with you - Castrol's Syntrans 75W-85 would be a good choice. these gear lubricants are amongst the best ever produced. I have tested and used them over many years and millions of kms

 

[frenchian]

I've ordered some Syntrans - the price I got seems too low (£4/litre for 20 litres - around $7/litre - it's usually twice that in UK) so I'm waiting with bated breath for it to arrive. The advantage of the Syntrans is that I can use it in the diffs and portal axles too.
I've also ordered some Shell Rimula R3X 15w40 for the engine as we're going to be in areas with high-sulphur content diesel.
Charlie - do you know what the recommended engine oil change interval under these conditions should be? I'm assuming that I'll need to do an oil change about 1/2 way which should place us in Nairobi - Shell have a major centre there so I should be able to get some more.

Thanks to all for your inputs - it's given me the confidence to "ignore" the manual!

Ian

 

[m37charlie]

Hard to know regarding change interval on an older motor, but it would be longer if you used R5M or R6M because that has a significantly higher acid neutralizing power than R3X (effectively good for up to 1.5 to double the mileage).
With R3X (TBN 11.5) - about 10,000 mi
With R5/6M (TBN 15.9) - about 15-20,000 mi.
If the engine burns some oil (mine uses 2.5L/6300 mi) that actually can lengthen the oil change interval (OCI) due to (dis)continuous infusion of new oil.
DON'T use Syntrans in the diffs and portals - it is only a GL4 transmission fluid, not enough extreme pressure additives for diffs and portals. Use a GL5, preferably synthetic 75W90 on the page 235.8 list.

Charlie

 

[frenchian]

Thanks for that Charlie, 10k miles should get us to Nairobi via a bit of a zigzag, then another 10k home depending on which way we end up going! At least a third of the 1st section will be in South Africa/Namibia where sulphur levels are low, so that will extend the life too. From Nairobi home there is at least 5k miles with high sulphur diesel, so maybe I'll go for a higher TBN oil at that point. Interestingly it was Shell themselves that recommended R3X instead of R5/6 based on the vehicle/route.

For some reason I thought that Syntrans was recommended for the portals etc - but I was going to double check before filling(!) - I've just looked at my top-up bottle and it's a 75w90 GL5 so I must have known already (age is setting in?). Looking at the manual it states 2.5l for the diffs - it seems to be for both (2.5l in a single diff would be a lot) - do you know this too by any chance?

Thanks again,

Ian

 

[m37charlie]

It is probably 2.5L per diff, plus 3-600ml per portal.
So figure up to 8.5L needed. Portals can develop leaks which must be kept with, so buy at least 10L so you have leftovers.
Carry some extra portal outer seals and diff pinion seals.

Charlie

 

[frenchian]

Thanks,


The manual is clear for the portals - 300ml each. I carry top-up oil for the portals wherever I go.
I've got spare seals (but only 1 of each) - sounds like I should buy some more.

Ian

 

[Vikas]

Where are your Unimog pictures? Isn't that the thing which climbs vertical walls???

 

[vinu_neuro]

Originally Posted By: m37charlie

Mercedes recommends
http://bevo.mercedes-benz.com/bevolisten/bevo-sheets-sort1.html
sheet 231.3, page 1
75W85 for basically all Unimogs except the BW 435s, where 10W is recommended.


I came across this sheet as well looking for something else. The way I interpret this table is that those recommendations apply to the military 10W spec as well. 235.1 is the preferred set of grades. And considering where he's going, their recommendation is SAE 90 or 85W-90.