A Series Diesel Engine Base Engine Components 159
Head Gasket Sealing
If the compression was found low on adjacent
cylinders and the pressure cannot be increased by
oiling the rings, the head gasket is probably leaking
between the cylinders.
Low compression on a single cylinder can be caused
by an external leak or a leak to a coolant passage.
A compression leak to the coolant will normally be
detected by loss of coolant as the coolant is blown
from the cooling system.