OP-
I think this is a thread that might be helpful:
http://www.peachparts.com/shopforum/diesel-discussion/350381-w124-coolant-system-pressure-gauge.html#post3277660

Mxfrank-
If your statement is true, then an awful lot of OM603 owners have wasted money replacing cracked heads when they should have replaced their radiator. In other words, yes, there are other ways you could have a pressurized cooling system in the morning.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).