Hans said no more than 13 or 13.1, above that you risk engine failure. The 60x engines are designed for 13.9, one of the reasons they have more power.

Peter

__________________
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!