THE PILOT INSTALLED AN INCORRECT OIL TEMPERATURE GAUGE. THE UNIT FIT INTO THE OIL SCREEN AND WAS SECURED BY PULLING THE CAPILLERY LINE TIGHT WITH TIE WRAPS. THE PILOT DEPARTED WITH HIS NEPHEW AND THE AIRPLANE WAS OBSERVED TRAILING SMOKE. LATER, IT WAS SEEN FLYING TOWARDS THE AIRPORT WITH NO SMOKE VISIBLE. THE AIRPLANE WAS THEN OBSERVED TO MAKE A SHARP LEFT TURN, ENTER A SPIN, THEN IMPACT IN A DITCH NEXT TO A ROAD. THERE WAS NO EVIDENCE OF AN ENGINE FAILURE; HOWEVER, ONLY ONE PINT OF OIL WAS FOUND IN THE ENGINE. OIL WAS FOUND ON THE UNDER BELLY OF THE AIRPLANE. ALSO, AN OIL TRAIL WAS FOUND THAT BEGAN AT THE AIRCRAFT TIEDOWN AREA & EXTENDED TO THE RUNWAY, WHERE A PUDDLE WAS FOUND IN THE AREA BELIEVED TO BE USED BY THE PILOT FOR ENGINE RUNUP. WITNESSES INDICATED THE PILOT PERFORMED HIS OWN MAINTENANCE ON HIS AIRPLANE.