The P W JT9D had a breather temp guage.
I believe the idea of the breather temperature is related to determinig if combustion of the oil is taking place in the breather which then has a nasty habit of burning through the breather tubing and setting off the nacelle fire system.
Health is related to wear and deterioration of the sealing characteristics,
letting too much hot high pressure air in which lead to high breather pressures and blown out oil loss over many flights.