The analog cockpit version reports the proper oil temperature (the one calculated by REP). The G1000 version, instead, can only report the default internal oil temperature of X-Plane, which is totally useless in REP’s case.
This is a known issue. Even tho REP totally overrides the default engine, X-Plane does not allow it to write some datarefs such the oil temperature and pressure. This means that in the analog version REP replaces the indicator which then shows the right value. In the G1000 there’s no way to trick the value shown to the user so the instrumentation reports the default oil temperature, even tho it has no operational value. The default oil temperature, in fact, is totally useless as the engine in use is not the default one.
EDIT: updates on this matter here
← I experience very high oil temperatures in the C172 G1000 version