The coked oil in the intake can get pretty thick -- I've heard of the intake ports being almost completely closed off, and on my mechanics "rescue" 740 TD, the crud was over half an inch thick. Greatly reduces air flow, even pressurized.

Best preventative is probably synthetic oil, as it doesn't coke.

I would get it cleaned out, as there is some suspicion that bent rods on the 3.0L 603 may be due to chunks of the glassy carbon going down the intake and not crushing enough. I don't see how this could be the case, but hey, anything to prevent a bent rod.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!