Cardinal 177/177RG
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 24; Flight Crew Total 2359; Flight Crew Type 1980
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Diverted; General Maintenance Action
Aircraft
Cruise altitude 8000 ft. from ZZZ to ZZZ1. Given crossing clearance of 4000 ft. 20 NM before ZZZ1. During 16 minute descent oil pressure suddenly dropped from 59 PSI to 40 PSI and oil temperature rose 33 degrees. I advised ATC and asked for vectors to closest airport ZZZ1 which I rejected in favor of KLOT for a more favorable runway. During this event I was given additional altitude clearances that I did not comply with because I wanted to conserve a higher altitude in case of catastrophic engine failure. I was in communication and radar contact with ATC during the entire event and am grateful for their assistance.
Pilot reported that oil pressure dropped to 40 PSI and oil temp rose 33 degrees; causing a diversion.