An air cycle machine with a bearing monitoring system comprising: a foil air thrust bearing (308, 310); a foil air journal bearing (312, 314); a flow passage configured to permit cooling air to pass over at least one surface of the foil air thrust bearing (308, 310) and at least one surface of the foil air journal bearing (312, 314); a first thermocouple located in the flow passage at a first position upstream relative to the foil air thrust bearing (308, 310) and configured to measure a first temperature of the cooling air; a second thermocouple (318,320) located in the flow passage at a second position downstream relative to the foil air thrust bearing (308, 310) and configured to measure a second temperature of the cooling air; a third thermocouple (320, 326) located in the flow passage at a third position upstream relative to the foil air journal bearing (312, 314) and configured to measure a third temperature of the cooling air; a fourth thermocouple (322, 324) located in the flow passage at a fourth position downstream relative to the foil air journal bearings (312, 314) and configured to measure a fourth temperature of the cooling air; a control device in communication with the first thermocouple, the second thermocouple (318, 320), the third thermocouple (320, 324) and the fourth thermocouple (322, 324), the control device configured to (i) compute a first temperature gradient across the foil air thrust bearing (308, 310) from the first temperature and the second temperature and a second temperature gradient across the foil air journal bearing (312, 314) from the third temperature and the fourth temperature, (ii) compare the temperature gradients against a known value, and (iii) if a temperature gradient exceeds the known value the control device is configured to provide an alert. a foil air thrust bearing (308, 310); a foil air journal bearing (312, 314); a flow passage configured to permit cooling air to pass over at least one surface of the foil air thrust bearing (308, 310) and at least one surface of the foil air journal bearing (312, 314); a first thermocouple located in the flow passage at a first position upstream relative to the foil air thrust bearing (308, 310) and configured to measure a first temperature of the cooling air; a second thermocouple (318,320) located in the flow passage at a second position downstream relative to the foil air thrust bearing (308, 310) and configured to measure a second temperature of the cooling air; a third thermocouple (320, 326) located in the flow passage at a third position upstream relative to the foil air journal bearing (312, 314) and configured to measure a third temperature of the cooling air; a fourth thermocouple (322, 324) located in the flow passage at a fourth position downstream relative to the foil air journal bearings (312, 314) and configured to measure a fourth temperature of the cooling air; a control device in communication with the first thermocouple, the second thermocouple (318, 320), the third thermocouple (320, 324) and the fourth thermocouple (322, 324), the control device configured to (i) compute a first temperature gradient across the foil air thrust bearing (308, 310) from the first temperature and the second temperature and a second temperature gradient across the foil air journal bearing (312, 314) from the third temperature and the fourth temperature, (ii) compare the temperature gradients against a known value, and (iii) if a temperature gradient exceeds the known value the control device is configured to provide an alert.