I'm sure it's not a pressure problem. Bad gasket on the oil filter. That or it is possible when the old filter was taken off the gasket for it didn't come off with it. When the new one is put on it won't seal correctly. Go buy a new filter. Take of the old one and look at the gasket for defects. Also make sure there is no gasket left on the oil filter mount.
most likely heater core leaking
where is the fuel pressure regulator on1991 lumina 3.1 /
have system pressure tested to observe leak
If the pump is leaking or noisy then assume it is failing.
Sounds like head gasket is leaking
you likely have a leaking heater core. Is this on the inside of the vehicle? if so then it defintately is a leaking heater core
i had this problem the intake manifol gasket is blowed
Oil pump driveshaft (also referred to as distributor) o-ring is bad. Replace, and oil will stop leaking there.
Change your thermostat. Mine had the same problem and it was stuck open.
ask a mechanic to do it for you
Your leak could come from any part in the system ,if your serp belt is oil soaked ,the most common cause is the output shaft seal behind the pulley on the pump. Another common leak located underneath the vehicle could be the return line which runs from the pump to the front frame rail the to the rack (very common for leaking) Also either pressure line or rack could be leaking .
A small radiator leak can cause antifreeze to leak on your 1998 Chevy Lumina when there are not any spots on the ground. A pinhole in a hose can also cause this.