THE SMALL EXHAUST MANIFOLD THERMALLY CONTROLLED VALVE USED TO PREHEAT INTAKE MANIFOLD WHEN COLD FAILED IN THE OPEN POSITION CAUSING SEVERAL ENGINE COMPARTMENT FIRES PLUS EXHAUST GASSES ON THE RIGHT SIDE OF THIS SIX(6) CYLINDER ENGINE RESULTING IN OVERHEATING OF FIREWALL AND PREMATURE FAILURE OF THE ALTERNATOR. EXHAUST NOISE IS EXCESSIVE. VEHICLE WAS IN MOTION IN BILLINGS, MT AT THE MOST RECENT FIRES.