Rant on Oil

Use Synthetic!

That said...
We started using a 0W30 Esso Synthetic oil in all of our engines because it made them start so much easier in the winter.   Then, Walmart stopped carrying it and the only way we could get it here was by the litre at the gas station which proved prohibitively expensive.  We then switched to Esso Delvac 1 5w40 synthetic.  It's still expensive, but the UniMoG only gets it's oil changed 2 or 3 times per year, so it's reasonable and we get a good temperature range.  This is convenient since we can see a 30 degree Celsius temperature change in a week long trip where we go.

We used to use Amsoil synthetic gear lube in the MOG just to give the gear box as much help as possible.  Mercedes does not recommend this however because the seals aren't designed for it which causes excessive leakage.  We monitored the consumption carefully and calculated the annual cost of the fluid.  It did not break the bank.

After we replaced the transmission, we switched to Pennzoil GL-4 for a while.  This was based on further research into the various oils and their effects on the vintage gear boxes.  When you have just purchased a new UniMoG transmission, you think carefully how to make it last.  The material specification from the oil manufacturer specifically states that the GL-4 oils will not cause problems with bronze bushings. (Here is the link to the Pennzoil data sheet)

We had also noticed that once we started using Amsoil in our old transmission, the syncros got much worse!  The evidence suggests that the Amsoil was either attacking the syncro ring material like a conventional GL-5 oil, or it was too slippery and did not provide enough friction for the syncros to operate properly.  Either way, we were not happy with the results.  After switching to GL-4 in Giggles, we were able to perceive in improvement in the operation of the syncros, so all may not be lost if you've made the mistake of using GL-5 in your old gearbox for a while.

In the new transmission, all six syncros work great and at 11,000 km, the gear box was not losing a drop of oil in a 4,400 km trip! (not bad for a German vehicle.)  We did notice, however, that the gearbox runs a little hotter than the old one.  Maybe this is because it is new with close tolerances, or maybe the Amsoil gave an advantage.  At this point we are willing to drive slower to reduce the heat and have good syncros and no oil leaks.  We also now change our transmission oil once a year whether it needs it or not.

In 2005 we changed all of our oils (in everything we do the oil changes on) to Royal Purple Synthetics.  We were able to get the oil at a screaming hot deal!  The oil temperature on the transmission improved with the switch and the syncros seem to still be happy.  The transmission began to slowly lose the top 1/2 litre of oil somewhat quickly, but kept the rest in the gearbox for extended periods of time.

In 2010 we changed back to Amsoil after losing the opportunity to get dealer pricing on Royal Purple.   SAE 10W-40 Synthetic Premium Protection Motor Oil is appropriate for use in Gasoline, Diesel, and Motorcycle engines, so we've been able to standardize on one engine oil for the Mog, Sprinter, and bikes - Amazing!!!

Here are good web sites for oil comparisons and oil filter comparisons