188. If a valve seat insert, similar to that shown in the illustration is cracked, this may be indicated by __________

A cracked valve seat insert allows cooling water to leak into the combustion chamber, resulting in white vapor in the exhaust gas. This is due to the water flashing into steam as it exits the hot exhaust system. Other options are unrelated to valve seat insert cracks; high pyrometer readings indicate overheating, spring surge is a mechanical valve issue, and a jammed indicator cock is a separate mechanical problem.