Thanks to all for the answers.
NickLappos
The checks are performed in cruise flight.
To remain within the JAR OPS 3 requirements Performance Class 2 - 150 ft/mn @ 30 mn power rating - the T/O mass has been reduced from 4000 kg to 3600 kg.
The difference with the specs and the second engine is significant so the impact of the OAT gauge is not the factor here.
The manufacturer does allow a slight drop of performances due to erosion or dirt - this is what tolerances are meant for IMO, but only up to a point.
"One degree of OAT rise is about 4 degrees of engine temp"
Is this a general rule and is it linear ?
Genghis
I can't understand how an engine can be out of tolerance and still be within performance certification. I believe if an engine is declared out of tolerance that's precisely because it cannot provide the certification performance level, or is it just a matter of wording ?
Thanks again
ATN