Cessna 210 Centurion / Turbo Centurion 210C; 210D
Flight Crew Private
Flight Crew Last 90 Days 45; Flight Crew Total 935; Flight Crew Type 475
Situational Awareness
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Flight Crew Landed As Precaution; Flight Crew Overcame Equipment Problem; Flight Crew Became Reoriented; Flight Crew Diverted
Human Factors; Aircraft
Smelled smoke in cockpit; determined source was inside aircraft. As situation developed; visually observed smoke as well. Engine instruments indicated nominal. No fire observed. Performed partial electrical system shut-down (radios; moving map; intercom; etc). Diverted to uncontrolled field. Once clear of Bravo airspace 30 NM ring; powered off transponder and switched master off. Ventilated cabin by opening window. Continued diagnosis effort during expedited descent; passenger used smartphone to photograph under dash. Gear retraction handle observed to be very hot. Passenger observed hydraulic hose to be very hot. Sight glass to hydraulic reservoir found to be too hot to touch. Gear selector handle found to be in 'up' position (not as expected; should have returned to neutral after gear retraction complete). Pilot flying manually moved handle to neutral. Turned master switch back on for landing; gear extension was normal and safe landing achieved at diversion airport. Did not need to manually extend gear. Source of smoke determined to be overheated hydraulic fluid and/or jacket material of hydraulic hose. Suspect intermittent failure of handle release solenoid; which prevented hydraulic pump from going into bypass mode; thus overheating the fluid.
Cessna 210 pilot reported diverting to an alternate airport after experiencing smoke in the cockpit related to overheating hydraulic fluid.