EGT's exhaust gas temp ! This is why the Pyrometer is important , low temps means the exhaust is contained within the engine and normally a valve adjustment is called for , other end of the spectrum where the exhaust gas runs too high we back out of the throttle and let the temp come down . There is a situation where the turbo "runs away" meaning you cannot shut down the engine and the engine will run at maximum rpm's till it disintegrates , it is difficult to put it into a high gear at these rpm's so stalling the engine is difficult , anyway , you need to stall the engine within a minute of this happening , if not , coolant will be pumped out and the oil will degrade and the engine will seize . Check this video out ....