It was in the context of the radiator being clogged and unable to dump the heat.
"An adiabatic process occurs without transferring heat or mass between a thermodynamic system and its surroundings. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work."
Wasn't looking for the definition, having studied thermodynamics as an undergrad, just surprised that a nonfunctional cooling system might be cast in such terms. Like, you don't start by noticing the engine's increased thermal efficiency as a stepping stone to realizing the radiator isn't getting hot or the water pump is failing to pump.
"An adiabatic process occurs without transferring heat or mass between a thermodynamic system and its surroundings. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work."
https://en.wikipedia.org/wiki/Adiabatic_process