Cessna 402/402C/B379 Businessliner/Utiliner
Flight Crew Multiengine
Situational Awareness; Distraction
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; Flight Crew Diverted
Human Factors; Procedure
I departed the airport [and] on the climb out as I was making my turn to the north at about 4;900 feet; I looked over at my right engine and noticed that the right engine oil cover was open and that oil was leaking out of it. I was in VMC conditions; I cancelled my IFR flight plan and returned to the airfield VFR. I landed the plane with no issue. I still had engine power and I proceeded to taxi the plane to the terminal to allow the passengers to get off. Then I taxied the plane to the hangar and wrote it up. Once I got out to inspect the plane; I noticed that the oil dipstick was missing.When I was doing preflight; I put a quart of oil in both engines. I remembered securing the dipstick in the left engine but not in the right engine. However; I do remember closing the oil cover and I don't recall the oil cover being open during start up and taxi.  After having to do preflight outside and brush off snow on my second plane; it is possible that I forgot to secure the right engine oil dipstick; and that is what caused the oil leak.  Even though I was a worn out and cold; I should've gone inside and warmed up before putting oil in the plane. I could've taken breaks between doing preflight; brushing off the plane and putting oil in the plane in order to give every task my full attention. When flying by myself that is something that I will do next time.
A Cessna 402 pilot reported observing an open engine oil cover with oil spilling out while in flight.  The pilot decided to return to the departure airport to remedy the problem.