Depending on your engine and type of vehicle, the exhaust manifold can either be a set of pipes or it can be a cast iron manifold assembly. Essentially the exhaust manifold takes the burned exhaust gases from the engines cylinders and ejects the gas through the exhaust system and out through the cars tail pipe. The exhaust manifold gasket seals the surface of the exhaust manifold to the surface of the cylinder head, preventing leaks in the system. Over time, the constant expansion and contraction of the components (caused by constant heating and cooling in the engine), may cause the gasket to leak. These leaks can be hazardous as hot exhaust gases escape and can damage other components in the engine compartment. A leaky exhaust manifold gasket can also impact engine performance. So replace your gasket and regain back lost performance. For FORD CROWN VICTORIA 1992-2011 FORD E-150 1997-2014 FORD E-250 1997-2014 FORD E-350 1997-2015 FORD E-450 2000-2015 FORD ECONOLINE SUPER DUTY 1997-1999 FORD EXCURSION 2000-2005 FORD EXPEDITION 1997-2004 FORD EXPLORER 2002-2005 FORD F-150 1997-2010 FORD F-150 HERITAGE 2004 FORD F-250 1997-1999 FORD F-250 SUPER DUTY 1999-2004 FORD F-350 SUPER DUTY 1999-2004 FORD MUSTANG 1996-2004 FORD THUNDERBIRD 1994-1997 LINCOLN NAVIGATOR 1998-1999 LINCOLN TOWN CAR 1991-2011 MERCURY COUGAR 1994-1997 MERCURY GRAND MARQUIS 1992-2011 MERCURY MOUNTAINEER 2002-2005 4. 6L 5. 4L