Unimog hub temperatures


Hello everybody, I upgrade some weeks ago the final ratios on my truck whit a nice result I can now keep 95 km /h as a cruising speed, but Im very surprised whit the temperatures I have now on the hubs , I atach some pics from the termocamera, so I made some reflexión and I would like the opinión from US, in my opinión all the staff I can found to solve the migration , just makes some delay of the problem and I Will say my opinión, the main problem is the small capacity of oil, so at the end to send again the oil on the hub its not the solution, because It is still overheat, so my idea is to monitor all the temperatures and stop when It needs, very simple, but my question is, which temperature can I consider as a save?

Pic of front hub out rim view

Pic of front hub internal rim view


Pic from rear hub...

The rear is much cooler than the front one , but not just a few degres, the front is 118 and the rear just 44, this test is after 75 km at 95 km/h in a hiway, any opinión Will be a help for me thanks



That is really hot, my front ones seldom get over 50 Deg C, the rear ones can get to 85-90 Deg C after a long run on the highway. Hottest I have seen the fronts was 75 Deg C and that was when it was 48 Deg C ambient temp.


I can imagine I have a problem whit the bearings, thats why the fricción is Hi, tomorrow I Will check the oil...maybe It gets me more info, thanks Ian for the reference, but where did You check the temps? Because I have this temps on the centerhub


I check on the rear of the portal box and the centre hub with a thermal heat gun. On mine it is similar. Every time I stop on a long run, I walk around and touch the centre hubs, the fronts are always cool, only on occasion are the rears hot enough almost burn my fingers That is usually after 100kph with air temps over 35 deg C.

I would check your portal oil for metal bits. All our trucks are getting old now, maybe someone will come up with a way of sleeving the bearing surface on the gears.
I have an Atlas temp measurement system. The thermocouples for the portals are at the drain plugs. The U500 is only 12 yrs old but has over 160K km. The temperatures with sustained 93-95kph are all about 25C over ambient, rears 2-3C over fronts. They hold 700ml oil. Actually the hot spot is the diffs, up to 70C over ambient, front slightly warmer than rear (fulltime 4WD).
You probably need to dis-assemble and carefully inspect the hot portal (s).
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Yes , I Will do, now I have two references, something is wrong on my portals, Rear are on the average like yours and Ian, but front are to Hot, thanks


So ok , oil changed, from last change 1400 km , 90% ok hiway, the oil on both sides dirty but I Think is normal for the quantity

The quantity was a surprise for me , last time I fit 300 ml and was a bit less
Right side

Left side

The magnets has no metal , just some metal frase


So , I Will wait until Next trip, Im planing to make this week some small trip arround 1000 km , by the signals the portals looks ok, I expect to find some metal on the oil.,..


I think you are losing oil on the left side, I made up a breather to recirculate the oil - the big pipe runs up to the top of the portal, and is attached to the OEM breather - drilled a hole in the big pipe and soldered the little pipe into the side of it.

2018-03-25 19.53.32.jpg

I'll get a photo of what I made tomorrow


Thanks Ian, thats true , in 1400 km I loss 100 ml , but is on the differentials the oil, because the Big seals on the hubs are New, they were lacking oil And Allready replace theme, so is a migration problem, Im thinking to build a reservoir to increse the oil capacity to one liter, there is space enought to build one aluminium tank, I Will keep You inform, Next half month I have many work trips....


Found It!!!! One brake líne, the Flex one betwen chasi and transmisión was damage when the gearing was fited , so the presure was comimg back slow, this morning we fit gauge in two places to found It , thanks all of you foto the opinions

VGE 3.0

New member
Hello everybody,

In my opinion, there are three reasons for increased temperatures in the portals.
Excessively high temperatures can occur due to high braking power. Defective bearings and gears also generate high temperatures.
If the constructively provided oil volume is too low, the temperature also increases because it can no longer be sufficiently dissipated.
If the seals are ok and the gearbox is healthy, there may still be a loss of oil. At speeds above 80 km / h (oil temperature is greater than 50 ° C), the oil starts to foam.

My friends and I believe that the oil is then lost through the standard venting in the axle.
To prevent this, we have a solution by a good friend (Franz Murr, died in 2012) slightly better and rebuilt.

Our solution looks like this:

Vorgelegeentlüftung Vorne 01.jpg Entlüftung Vorderachse .jpg

For vehicles using the vents, the oil consumption is stopped.

I'm new here in the forum, write the post in English and hope that this time it will be displayed in the original. :)

Kind regards


Active member
This is a beautiful - as is Jostt's reservoir. I love seeing such well made solutions. I have to ask how much of a problem oil loss in portals is? I will be getting my mog soon and want to understand as much as possible in advance so knowing if the oil loss/migration issue is very common or rare would be useful.

All the best


VGE 3.0

New member
Hello Nathan,

and want to understand as much as possible in advance so knowing if the oil loss/migration issue is very common or rare would be useful.
Your question is not easy to answer.
I know of some UNIMOG, where the problem of oil migration does not exist. But I know many UNIMOG who have the problem.
Many travel UNIMOG owners drive fast axles and / or a split gearbox.
Often long hours are driven on highways.
At high speeds, the portals generate higher temperatures and many owners retrofit a portal vent. As a prophylaxis and for a safe feeling. :)
UNIMOG working in agriculture or in the forest will not get the problem of oil migration. For such application, the older UNIMOG were also constructed.

I could not drive my UNIMOG 1300L, EX-fire engine (OM 352A) for a long time, because I am still working on the conversion to the camper. On the first short rides, I have closely watched the oil levels. The temperatures were always less than 40 ° C.
I would recommend that to you.

Kind regards from Germany
i think the "oil migration problem" may have more than one cause. In my U500 I was having 20ml/1000mi moving from the right rear to the rear diff. Staiger in Karlsruhe replaced the right rear axle shaft (slightly bent) and sealed bearing and over the next 7000 mi oil migration from right rear portal seems to have stopped. This particular thing seems to have been steady for over 100K km.
One evening NW of Moscow I noted loss of about 300ml from left front due to leak around inner portal seal. Adding Penrite Syn Gear Oil with high ester content (esters cause seals to swell a bit) temporarily stopped it but Staiger replaced the seal.
The failure of www.whiteacorn.com U500 right rear portal in Iran from no oil in the portal MAY have had a similar cause. At any rate a temp monitor system will probably prevent catastrophic failures due to no oil. I now have the Atlas system, I like it.
Murphy's law corollary says now that I have the monitor system no further problems will occur.


Hi Charlie, what sensors does the Atlas system come with? I have a Blue Sea systems temperature monitor and I used epoxy glue to stick on the sensor to the portal casing. I had the rear brake pad get stuck, causimg the temperature to risequite a bit, got to 70 Deg C by the time I found a safe place to pull over. Normal temps are about 20 Deg C above ambient aand the front ones are normally around ambient unless I've been braking.

2018-03-29 10.30.25.jpg