Today's mineral oils are WORSE for diesel engines than they used to be! Sometime ago in the early-mid 90's the CF (diesel) rating was removed from oils such as Castrol GTX 20W50. Today, the Mobil 1 and other synthetics continue to carry the light-duty diesel rating (CF) or the Euro B3/B4 ratings. So, IMHO anyone running mineral oil should be changing oil every 2500 miles.

By comparison, the synthetics that Tasma and others are using are CH-4 rated. These oils are designed for heavy-duty diesels. They can tolerate a lot of abuse, have very high additive, dispersants, and detergents, and high TBN to neutralize acids for a long, long time. The oil analysis tells how much water is in the oil, and the amount of oil additives remaining in the oil. It reports on the oil's ability to neutralize acids (TBN). When the oil turns bad, it thickens (mineral oil) or thins out (synthetic oil). Too much soot will cause either oil to thicken. We aren't talking about mineral oil which I'd change every 2500 miles. This is synthetic. The newer cars are all specing synthetics and thinner synthetics at that. There are 300D's (603.960) engine that the owner changed oil every 9000 miles (3000 miles/fltr) using Delvac 1300S 15W40 (non-syn, CH-4) and the engine has 831,000 miles. (I have photo of odo).

That said, do whatever makes you happy.

Lube in peace,
Brian

'87 300D 244Kmi