Flight manual.
With the P-37 engine an altitude will eventually be reached during the cruise climb where the engine is operating at idle RPM, the exhaust gas temperature is up to the rnaxirnum, and the aircraft is still climbing. When this condition occurs, prompt action must be taken to prevent over temperature operation of the engine. Initially, the condition may be corrected merely by allowing the aircraft speed to increase while maintaining constant altitude. When the speed has increased to a point within 5 knots of the needle, aerodynamic drag should be added. The initial drag is created by using the variable speed brake or extending the landing gear. As the aircraft descends, engine power is increased to maintain engine operation at maximum limitations. Eventually, the aircraft will cease descent and again begin a cruise climb. When the aircraft again reaches the altitude of limiting conditions, the remaining drag devices will be used.
The P- 31 engine will normally never reach an altitude where idle RPM is encountered. However, maximum altitude is limited to the point where maximum exhaust gas temperature is reached and power cannot be further reduced without dropping below the minimum engine pressure ratio limit. The corrective procedure is the same as outlined above for the P·37 engine.