in what form is waste heat expelled from an automobile engine?
The form is heat. The means are through the radiator and heater cores (heat exchangers)
Exhaust, radiator, convective heat transfer from exhaust manifolds, etc to surrounding area in engine compartment.
Scott H. and kasab are correct. The exhaust stream represents the overwhelming majority of waste heat removal. The lubrication system is a small but vital heat sink as well.
Through hot exhaust gases and radiators which are heat exchangers using air as the cooling media.
