The engine has seven cylinders; symptoms are on a single unit. For diagnosis, additional information would be: load/speed, the specific cylinder's exhaust gas temperature, jacket cooling water inlet/outlet temperatures at that cylinder, Pmax/compression pressure measured on a draw card, fuel pump index, and the condition of that unit's injector.
Probable defects: over-fueling of that cylinder (faulty fuel injection - leaking/dribbling injector, worn plunger, large rack index, or the injection timing retarded), late ignition, poor combustion, leaking exhaust valve, loss of compression (stuck ring, worn liner, burnt head gasket/blow-by) reducing power and so the other cylinders carry the load. Also scavenge-air starvation to that cylinder (blocked air ports) giving incomplete combustion and high exhaust temperature. Could also be a leaking or burnt exhaust valve.
Action: Take the cylinder's power out (reduce the fuel pump index/injection for that unit if individually adjustable) to bring exhaust temperature down; check the injector (atomization/leak-off), the exhaust valve seating, compression with a draw card; check scavenge air and charge air pressure; investigate with a single. Increase the load on other cylinders if possible, adjust the load distribution.
Probable defects: under-fueling of that cylinder (fuel pump fault - sticking plunger, broken spring, empty fuel line, plugged injector hole), retarded injection, too much air (air leaking in), or a leaking exhaust valve letting gas through early, or a slightly open injection dribble reducing fuel. Could be a stuck-open injector/needle or a faulty pump giving too little fuel.
Action: Check the fuel pump delivery/index of that unit, injector lifting, fuel rack; take a draw card to see the work done - if Pmax is low, the cylinder is starving; check the exhaust valve function and the fuel supply. Bring the exhaust temperature back up to the mean by adjusting the load/fuel feed to that cylinder.
Probable defects: reduced heat input to that cylinder (under-fueling, poor combustion), reduced water flow through that cylinder due to a blocked jacket passage, or a stuck closed outlet thermostat; also possible internal leak/air. A cold jacket on one unit usually means that cylinder is doing less work or the cooling water isn't circulating properly.
Action: Check water flow (bleed air from the jacket), compare jacket temperature with others; check for blockage; check the unit's injector and fuel feed; if water flow is restricted, the cylinder will overheat locally even if outlet is cool - investigate carefully; re-circulating pump faults.
Probable defects: This indicates excess heat input to that cylinder or reduced cooling (blocked water passage, salt/scale, fouled jacket, throttled outlet, air lock, defective thermostat/circulator), and could correspond to over-fueling/poor combustion in that cylinder, overheating, or a scavenge/exhaust heat feedback. It may also be the beginning of a scavenge fire in that cylinder leading to high liner heat.
Action: Check water supply and circulation to that cylinder, and the jacket temperature; reduce load on that unit; check injector, rings, combustion; investigate the possibility of a local scavenge fire (check scavenge temperature and exhaust) and act; ensure the cooling water pump/circulator state; check for air lock and confirm the cylinder liner is not over-heating leading to damage.