what causes build up in crank case and blows the oil out?
It is a 4.9 , 6 cylinder
Is your PVC valve functioning correctly? Clean it out or replace it but you have just have excessive blow by due to worn rings.
Check your PCV system, could be the valve is plugged or the vacuum line to it, then make sure the PCV filter, tubing and fittings are in good repair, if all that checks good then either it is being over revved or the rings are shot. Remember these engines are torque motors, they are not designed for speed, the straight six's peak horsepower is 150hp @3400 rpm and peak torque is 265@ 2000rpm.
Just being an old worn out motor causes this
Looking for a Used F-150 in your area?
CarGurus has 212,369 nationwide F-150 listings starting at $1,000.
Search Ford F-150 Questions
Ford F-150 Experts