Do you check the transmission fluid level on a 1988 Olds Delta 88 with engine stopped or running?

You should check the transmission fluid level on a 1988 Oldsmobile Delta 88 with the engine running and the car warmed up. Unlike some older cars, many automatic transmissions of this era require the engine to be running to accurately measure the fluid level because the pump needs to be operating to circulate the fluid and get an accurate reading. Consult your owner's manual for the specific instructions for your vehicle, but generally, running and warm is the correct procedure.