why would the radiator get pressure on a cold start
Head issue would be the first to pressure check,this should of showed and issue with the heads,cold pressure is a leak in the intake or head gasket.
how does the oil look/exhaust pipe ???!!!
Oil good and exhaust too no water.
I agree with T_S_T, if is likely a head gasket or cylinder head issue.
Looking for a Used Sentra in your area?
CarGurus has 52,583 nationwide Sentra listings starting at $700.
Search Nissan Sentra Questions
Nissan Sentra Experts