M-20 J (201) / Allegro
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 4; Flight Crew Total 216; Flight Crew Type 7
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
During cruise my passenger noticed smoke in the cockpit. I immediately saw oil spraying on the windshield. Within 20 seconds most forward visibility had been lost. I identified a possible forced landing site on the nearby beach in the event the engine failed completely or caught fire. The engine oil temperature [and] pressure; as well as the CHTs looked good; so I decided to attempt to make it back to [departure airport.] I declared an emergency on 121.5 and received no response; so I re-declared the emergency with TRACON. The remainder of the flight proceeded without incident and I was able to land safely and taxi to the ramp on my own power.On the ground it was clear that a substantial amount of oil had coated the windshield and horizontal stabilizer. Oil continued to leak around the exhaust. I suspect the oil contacting hot exhaust parts may have caused the initial smoke. I'd guess that the likely cause of the oil was related to the prop governor; which had earlier been showing signs of unstable RPM; oscillating about +/- 50 RPM from the desired setting. I should have recognized this deviation as a sign of a potential problem with the prop governor rather than normal slop.
M20J pilot reported probable prop governor problem resulting in an oil leak that coated the windshield.