Exhaust temperature rise may be because of various reasons considered to scenario
1. Excess temperature of all units increases
> Dirty turbocharger air filter
> Governor malfunctioning
> Problem with fuel oil that is fuel oil temperature decreases for fuel oil quality not good.
> Air cooler choked
> Scavenge air temperature high
2. Exhaust temperature of one unit increases
> Tappet clearance increases
> Incomplete combustion due to blow past
> Exhaust manifold got chock
> Leaky fuel injector
> Leaky exhaust valve
> Bad fuel pump timing and rack adjustment.