Narrative:

I arranged for flight following with approach prior to departure on clearance delivery frequency. Approach handed me off to [another] approach [controller]. At 9500 ft I happened to notice oil pressure dropping below the green arc. I immediately reduced power to idle; turned toward ZZZ and notified ATC for loss of oil pressure. Approach handed me off to tower. I made a 360 to lose altitude. I noticed the engine was maintaining about 5 psi of oil pressure. Temperatures were normal. There was no signs of leaks. I held hope all the theatrics were for an indication problem. There was no traffic. Winds were calm. ATC was professional. I executed the approach and landing as planned. A good day for my first emergency. Lessons learned: there was an oil leak. A clamp that holds an air scoop to the oil cooler failed in such a way to cause the oil cooler to leak. That arrangement has been on the airplane since before I bought it about 30 years ago. The mechanic will use hindsight to secure the scoop in a different manner. A lot of pilots/mechanics say that if you fill oil to capacity a lot will leak/blow out until it finds its own level. Adding oil above this level wastes oil and money. They say the O-470 in my plane will do just fine if you keep it above 8 quarts. That was true before I overhauled my engine. Now it uses little oil regardless. I had 10.5 quarts when I departed. I landed with 3-/+ quarts about a 1/2 hour later. I think I'll continue adding a case at oil changes for as much reserve at feasible. I generally utilize ATC. Having them immediately available was a good resource in this instance. Foreflight makes it effortless to file and close VFR flight plans and I usually use them. I didn't in this case because I established contact with approach prior to take-off. There is still a chance for a lack of flight following at the small airport that was my destination. I will re-consider my thinking on that.

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Original NASA ASRS Text

Title: Bellanca pilot reported an oil cooler leak that resulted in an emergency landing.

Narrative: I arranged for flight following with approach prior to departure on clearance delivery frequency. Approach handed me off to [another] Approach [Controller]. At 9500 ft I happened to notice oil pressure dropping below the green arc. I immediately reduced power to idle; turned toward ZZZ and notified ATC for loss of oil pressure. Approach handed me off to Tower. I made a 360 to lose altitude. I noticed the engine was maintaining about 5 psi of oil pressure. Temperatures were normal. There was no signs of leaks. I held hope all the theatrics were for an indication problem. There was no traffic. Winds were calm. ATC was professional. I executed the approach and landing as planned. A good day for my first emergency. Lessons learned: There was an oil leak. A clamp that holds an air scoop to the oil cooler failed in such a way to cause the oil cooler to leak. That arrangement has been on the airplane since before I bought it about 30 years ago. The mechanic will use hindsight to secure the scoop in a different manner. A lot of pilots/mechanics say that if you fill oil to capacity a lot will leak/blow out until it finds its own level. Adding oil above this level wastes oil and money. They say the O-470 in my plane will do just fine if you keep it above 8 quarts. That was true before I overhauled my engine. Now it uses little oil regardless. I had 10.5 quarts when I departed. I landed with 3-/+ quarts about a 1/2 hour later. I think I'll continue adding a case at oil changes for as much reserve at feasible. I generally utilize ATC. Having them immediately available was a good resource in this instance. Foreflight makes it effortless to file and close VFR flight plans and I usually use them. I didn't in this case because I established contact with approach prior to take-off. There is still a chance for a lack of flight following at the small airport that was my destination. I will re-consider my thinking on that.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.