I have an 1987 Blazer with 190,000 miles. Well serviced over the years.
It has developed low oil pressure, when warmed up only shows a few
psi. Pressure does go up when eng rpm is increased. Changed the oil
pressure sender, same results.
Suggestions?
Hp1

 

Probably either a weak pump or increased clearances on the main bearing journals due to age. Sounds like an engine rebuild is in your future.