Date: 201207
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Small Aircraft; Low Wing; 1 Eng; Fixed Gear
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Cruise
Airspace: Class G ZZZ
ATC / advisory: CTAF ZZZ
Aircraft component: Engine
Component problem: Improperly Operated
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Private
Human factors: Communication Breakdown; Troubleshooting; Training / Qualification
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; Flight Crew Landed in Emergency Condition; Flight Crew Diverted; General Maintenance Action
Contributing factors: Human Factors; Manuals; Aircraft
Primary problem: Aircraft

Narrative: I had just purchased a 1946 Ercoupe 415C from an owner who had chosen to sell it after her husband passed away and she (a pilot also) decided to stop flying at this time. A pre-purchase inspection was performed on the plane in my presence; and it's most recent annual was performed less than a year prior and was; therefore; current.Since this was a 'new' plane to me; I hired a CFI to accompany me on the flight back to my home base. He chose; and I agreed; to make the flight in two legs on two successive days. This way I could get a relaxing familiarization and training from him.I preflighted the plane with the previous owner utilizing the check list and her input as to details she and her husband had experienced. When we checked the oil she indicated the level they traditionally maintained was just below the 3 quart mark on the dipstick. It should be noted this plane originally had a Continental 75HP engine and at its last major overhaul; 130 hours ago; it was replaced with a Continental 85. After some thinking things through; this may have led to this entire oil level experience which follows.All was going well for the first 60-65 NM of the approximately 105 NM leg when I noticed the oil pressure was lowering and outside of the green range. I also noticed over the course of the next 5-7 NM that it appeared to be reducing and it was now at approximately 20 PSI. We decided to divert and; as we began a descent the pressure fluctuated and we ultimately landed the plane at a small single strip airport.Once landed; we discovered the airport was not manned at the time and; in fact; the single runway had been closed for resurfacing. The landing was safely made with no damage whatsoever. Upon landing we had intentionally stopped the engine to keep the engine from further running at low oil pressure.We checked the engine and oil level on the side of the closed runway and found it to be at a bit above the two quart level. We added a quart of proper multi-viscosity oil that was on board the plane and restarted the plane. Oil pressure returned to the normal range and no unusual issues surfaced. We then took; off and completed the remainder of the first leg without incident. Oil pressure stayed normal and; upon recheck; the oil level was above three quarts. We will be topping it off to the ultimate full mark first thing before flight tomorrow as the FBO was closed.We had had to make a decision to land at the nearest safe location and; frankly; were fortunate to be able to do so quickly. Attempted radio contacts; albeit a quick attempt; did not result in any response. We also did not notice a yellow 'X' that was painted at one end of the grass runway. We just did not see the 'X' when we were concentrating on landing safely. We only saw it after we took off. So; I am reporting this incident because I am concerned that I did; in fact; land on a closed runway.




Synopsis: On his first flight aboard his recently purchased Ercoupe the new owner encountered low oil pressure indications and diverted to the nearest suitable airport where he--along with an accompanying CFI who was performing a check out--landed on a closed runway. After adding oil and determining oil pressure was now normal; they took off and continued to their destination.