HAD LEFT WORK AND DRIVEN APPROX. 12 MILES DRIVING ON HIGHWAY. WHILE GOING THROUGH NEXT TOWN DRIVING AT APPROX. 35 MPH, DRIVER SMELLED SMOKE .PROCEEDED APPROX. 3 CITY BLOCKS AND PULLED VEHICLE OVER ON SIDE OF ROAD. UPON OPENING HOOD OF TRUCK, FOUND ENGINE ENGULFED IN FLAMES. TOTAL LOSS OF TRUCK DUE TO UNDER HOOD FIRE.