between the Tank and the I.P.

This engine has a "Fuel Thermostat" sitting on the support of the Driver's side
Motor Mount that has a O-Ring seal Notorious for going bad. it can Leak Fuel and Suck Air

Motor AND Tranny Mount(s). ???

Do you have a Clear PreFilter (The Little one) are there ENORMOUS amounts of
bubbles in there?

Any Oil in the Surge Tank? (Radiator Fluid)
(whitish smoke?)

How Many Miles on this Particular OM602 ?

__________________
'84 300SD sold
124.128