GMC 1995 Suburban Owner's Manual page 318

Adding Coolant
-
Diesel Engine
To Check Coolant
A
CAUTION:
Turning the surge tank pressure cap when the engine and
radiator are hot can allow steam and scalding liquids to blow out
and burn you badly. Never turn the surge tank pressure cap
-
even a little
-
when the engine and radiator are hot.
When
your engine is cold.
the
coolant level should be at the COLD mark. or
a
little
higher.
6-36