Ishida later retired with head gasket failure. This joint is sealed by a head gasket. This increased the overall reliability of the engine by improving head gasket sealing. White exhaust smoke is an indicator of coolant burning, another sign of head gasket wear. Sodium silicate can be used to fill gaps within the head gasket. Unfortunately the car was forced to retire with a blown head gasket. The lids can be welded or secured with a head gasket and bolt ring. The most common years of the head gasket issue, by far, are 1997-1999. Many Northstar engines became well known for their tendencies to experience head gasket failure. The bore was reduced for increased strength and improved head gasket sealing. This F8M second generation will unfortunately be weaker at the cylinder head and head gasket. Jarier/Ickx won the race and Pescarolo/Larrousse retired with a broken head gasket. Of note is a serious head gasket issue that remains unresolved by Subaru. Cylinder head to block sealing was by a head gasket incorporating Cooper Rings. Leak-down primarily tests pistons and rings, seated valve sealing, and the head gasket.