Mercedes Benz repair: Oil changes in an early 80s MBZ diesel, petroleum oil, arctic conditions

Question
I have owned a 1984 380SE.....have been able to fix some things...so when a friend of my mine had a problem in her early 80's diesel..which I was able to fix, she asked me how often the engine oil should be changed. I don't know! Could you please tell me the miles and interval that this should happen?

Thanks, in advance! Gerry Ascencio

Answer
Petroleum oil needs change every 3000 miles.

100% synthetic is generally 6000 miles, for the average driver.

Harsh conditions = desert or arctic conditions:
Desert requires special = 3000 miles or sooner as needed.
Arctic = lighter oil weight = 3000 - 6000 miles, or when temperature changes.

FYI: I use 100% synthetic oil in all personal vehicles.