Unimog Oils


As Sol would say 'Oils ain't oils' (a local 1970s series of Mobil oil adverts).

I have been trying to find the best oils for the 435 series Unimog. In particular, the U1700. Most seem to have been made around 1988 plus or minus a decade. I could not find any existing posts on the matter.

Oils have moved on a lot since 1988 mineral oils were the norm with semi-synthetics and even 100% synthetics. Some modern mineral oils are so good, they can be called synthetics.

Vehicle instructions state ‘hypoid trans oil SAE 90 (OEP-220)' (i.e. gear oil) for axles, hubs.
However, hypoid and most spiral bevel gears usually need a GL-5, yet GL-5 produces sulphuric acid that attacks white or yellow metal. I can only assume the diffs and portal hubs don't have white or yellow metal.
Can anyone confirm GL rating of 5 for gear oil?

Vehicle instructions state ‘engine oil SAE 40 (OMD-115)' for crankcase and transmission.

I have read that with old vehicles, the introduction of synthetics can cause some issues with seals, by dissolving the decades of crud that have built up in the internal surfaces (which can help to keep the seals sealed).
However, assuming that this is not going to be a problem, Can anyone advise what types of oils will suit this vehicle and be best for hot long runs across Australia?

Also, I cannot find a supplier of medium size home use containers of oils here in Australia (i.e. 50 or 60 Litres). Either piddling little 20 litre drums or very large unmanageable drums requiring a drum lifter crane (not suited for use around the home garage environment).
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World Citizen
I don't have answers for you other than....maybe you are overthinking this a bit? I use whatever oil is at hand and try to match the operators manual as close as possible..given the current choices. Seems to have worked for me (so far anyway)
Standard dino juice 80w90 in all drivetrain except the transmission which cleans up really well using full synthetic RedLine MTL. Once again dino juice 15w40 in the motor.
I'm running:

Full Syn RedLine MT-85 (75W-85) in the trans (really improved shifting) and meets the GL4 requirement.
Full Syn Redline 75W-90 GL5 in the axles and Portals
Full Syn Rotella T6 5W-40 in the engine.


This will tell you what you need to know re operating fluids.
Use something from the 235.8 list (all GL5) for diffs and portals if you want synthetic, likewise from the 235.4 (GL4) list (castrol Syntrans) for the gearbox. For the engine a 15W40 from the 228.3 list, or a 10W40 from 228.5 (synthetic).
If you don't want synthetic, use 80W90 or even straight 90 for the diffs and portals, must be GL5. Trans fluid must be GL4 and in the 75W85 viscosity range.
Synthetics do make diffs and gearboxes last longer but nothing is immune to water; must change ASAP if contaminated after fording!!!
And check portals often, some Mogs have an issue of pumping from the portal to the diff with high speed running, thru the breather lines. I check mine every 5000 miles.

The oil specs that came with the truck were for its' prior military usage.

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I'm running:

Full Syn RedLine MT-85 (75W-85) in the trans (really improved shifting) and meets the GL4 requirement.
Full Syn Redline 75W-90 GL5 in the axles and Portals
Full Syn Rotella T6 5W-40 in the engine.

Take care if You run the truck in a hot ambience 5w40 is like wather for These cain of engine the tolerances are not like now, I know many peolple hate heavy oils because You must warm the engine when cold , but...they are much beter when Hot, just one opinión, actually do You can find many semi syntetic oils , best compromise, I use 15w50
Re Penrite:
For the engine the Penrite HDR Diesel 15W50 looks good. For the gearbox I'd use the GL4 75W85, and the portals and diffs the GL5 75W90 full synthetic. I can tell you from personal experience that the esters in the latter caused a bad leak in my left front inner portal oil seal to stop quickly.

I've had great luck with the 5W-40 year around, and it gets 110 deg here in the summer. Oil pressure has been the same with this oil vs 15W-40, even at hot idle.