A DRIVER FOR OUR COMPANY WAS OPERATING A 2007 FREIGHTLINER CL 112 TRACTOR WITH 50,000 MILES EQUIPPED WITH A MERCEDES BENZ (MBE4000) WHEN THE ENGINE SUDDENLY CAUGHT FIRE. UNIT WAS BEING DRIVEN UNDER NORMAL OPERATING CONDITIONS WHEN SMOKE WAS SEEN COMING IN THE CAB. DRIVER PULLED THE TRUCK TO THE SHOULDER OF THE ROAD AND FLAMES WERE COMING OUT FROM UNDER THE HOOD. DRIVER TRIED TO PUT THE FIRE OUT WITH A FIRE EXTINGUISHER BUT WAS UNABLE TO CONTAIN IT. THE FIRE DEPT WAS CALLED AND DID PUT THE FIRE OUT. THE TRACTOR WAS COMPLETELY DESTROYED. AT THIS TIME NO CAUSE FOR THE FIRE HAS BEEN DETERMINED. *JB