Transmission Temperature

We travel a lot in the summer on the highways to get to our camping destinations.  This can be hard on a 40 year old vehicle.  The typical speed of traffic on the highways here is about 120km/h.  For a vehicle that was only designed to go 95km/h, this can be a poser.  On a hot (for Canada) summer day the UniMoG cannot travel at a sustained 90km/h without the transmission overheating.  Sometimes 80km/h is too much for it.

Our observations are approximate, because we didn't have an outside thermometer on the truck yet, but here is a summary of our observations:
Below about 20 degrees Celsius, the transmission seems to be able to maintain 90km/h.
Between 20 & 30 degrees Celsius, about 80 km/h is sustainable.
Above 30 degrees Celsius, you can't get much more than 70 km/h without overheating.
If the outside temperature is above 40 degrees Celsius, it is time for a siesta!  You & the truck will both appreciate it.

This knowledge comes from using Amsoil synthetic gear lube and a VDO temperature gauge.  The temperature that we use as a maximum for the transmission oil is 110 degrees Celsius.  This number is somewhat arbitrary, is come from some research that we have read on the breakdown of engine oil.  If anyone can ever tell us a BETTER temperature to use (with appropriate documentation) we'll be happy to change.

The MOG can climb a hill in 1st or 2nd all day under full throttle, but can't take high speed.  Let's all remember to stop and look at the view periodically on those hot days for the MOG's sake.  This has also led us to the theory that a larger engine like the 2.8L M 130 for more power on the hills would be just fine on the stock gear box, provided the driver keeps the speed down.