The oil doesn't seem to affect starting on the Deutz. The starter and battery are able to turn the engine over no problem. The unit is filled with motor oil, and that stuff doesn't gel up until it gets really cold. Pre-heating the oil would probably help more than using synthetic, but this would be more for helping the machine to run correctly faster. The big advantages of synthetic are as follows:
1. doesn't break down at higher temps, so if the oil gets overheated it will survive better.
2. Is more resistant to water.
3. Lasts longer while maintaining viscosity.
supposedly synthetic does not transfer heat as well, which is actually a bad point.
Glow plugs is definitely the way to go with the diesels.
The different formulation of synthetic does help -- you can get a larger difference between the two numbers in a blend when you use synthetic. Bottom line is that to get the same (or better) level of high-temp performance as dino oil, you can use a thinner synthetic, which is easier on the starting, in addition to the other benefits you mentioned...
Another difference is in the "shear" factor -- synthetics are much, much better. This is an issue with hydraulic gear motors, though not significant with hydraulic cylinders.
I changed to Amsoil, and noticed easier starting with my Kohler-powered 425, in addition to increased wheel motor torque when the oil was hot... there's several (at least a few) 422/425 owners on here who've switched to synthetic.
Still didn't give me all the torque I wanted though, and I ended up going to larger displacement wheel motors.
YMMV...
BTW, here's a good list of the benefits of synthetics:
Advantages of Using Synthetics
• Synthetics offer better engine wear protection, helping the engine to last longer
• They offer better
fuel economy helping you to save money at the pump
• They help your vehicle to start easier in cold weather due to its low pour point
• The engine runs cooler in higher temperatures by reducing friction
• There is an increase in horsepower
• There are less tailpipe emissions
• It helps to reduce engine deposits, which helps to make the engine perform more efficiently
• Synthetics help to resist oxidation and thermal breakdown which helps to reduce sludge that will cause the valves and rings to stick
• They offer better stability as then engine doesn’t burn as much oil because the oil is more resistant to the heat
• They offer better lubricity because the synthetic oil polymers can slide more easily together. By reducing this friction, you improve horsepower and torque but lesson engine wear.
• They offer better film strength – this is the resistance of oil molecules from separating under pressure. If you think about two metals being pressed together, with oil between them to stop them from grinding, you want that oil to stay there. Conventional mineral oils will push away from each other. As synthetic oils don’t shear as easily, they can maintain a higher film strength, which prevents wear under difficult and extreme operating conditions.
SOURCE:
http://www.autotropolis.com/wiki/index.php?title=Synthetic_oil