1986 Subaru DL • 4 cylinder 4WD Manual • 240,000 miles

I got an '86 Subaru DL 1.8 liter that has 240000 miles on the engine. My oil pressure is usually @ 40-45 psi @ 3000 rpm's. All of the sudden, I'm getting a loud clicking sound out of the motor(yes its is full of oil) and my psi's have dropped to 10-15 after the car gets to operating temp. What sends the oil through this particular engine, an oil pump or a sending unit? I know a bit about american engines and also know that japanese engines can be finniky and are different in certain aspects. What could I be lookin @ here?
December 8, 2010.

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