Exhaust gas temperatures high

Air inlet to cylinders too high, check air cooling for water circulation/temperature or tube stack blockages and insufficient venting.
Leaking air manifold / exhaust manifold.
Fuel Injection faults, possible late injection or non sealing nozzles.
Turbocharger filters choked or dirty compressor wheels, exhaust back pressure too high / economiser blocked.
Damaged turbine blades and nozzle ring.
Deposits on inlet or exhaust valves.