I have just purchased a 1999 E300 TD (~ 39,000 miles)and noticed that the oil, which was just changed by the MB dealer, was jet black. Is this normal for a diesel engine and is there a special type of engine oil required for diesels?

Yes and yes.

It's normal for the engine oil in a diesel to turn jet black five minutes after it's changed. I've had three MB diesels and they've all done this. I don't think this has much negative effect on engine life, but I only kept the first one until 250K miles The other two are still "new."

Your OM606 diesel engine does have some special requirements for engine oil. There are two aspects: 1) The oil must carry a CH-4 or CG-4 rating. This is a diesel specific rating somewhat like the SH/SJ ratings which apply to gasoline automobiles. 2) MB specifies only full synthetic oils be used for the extended drain intervals computed by the FSS system.

There aren't too many oils which qualify on both counts - one or the other, yes, but not both. If the dealer isn't using a synthetic CG-4 oil it's not that big a deal, but in such case I would recommend more frequent oil changes - perhaps 5K-7K miles rather than the 10K-12K the FSS system is likely to recommend.

I've been driving MB diesels for 30+ years and the new oil that was put in looked like the used oil that was drained out as soon as the engine was run and the oil checked on the dip stick.
I also have a Case Diesel tractor and the oil in that is always dark brown, even though it burns the same fuel. I can't explain why it is different. Another difference in the Case engine compared to MB engines is that the Case idles quiet like a gas engine and sounds like the hammers of hell under full load. Maybe its because the Case is a direct injection engine.
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