look at your radiator cap, it should have 140 stamped on it, indicating 140 millibars or 1.4 bars
Also called atmospheres, millibars are another unit of measure for pressure.
To convert from bars to psi multiply by 14.7 therefore 1.4 bars = 20.5 psi
Earlier diesels used 1.0 bar pressure caps, then the turbo diesels went to 1.2 bar finally the 603 went to a 1.4 bar cap. Higher system pressure allows the coolant to reach higher temperature without boiling.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!