Abstract: A device is disclosed for shutting off the flow of exhaust gases from the exhaust outlet of a diesel engine having a substantially vertical exhaust stack. The device is especially useful for stopping the flow from one of twin diesel stacks when a tractor or truck having twin stacks from a single manifold is undergoing maintenance in an indoor facility. The device permits an operator standing on the floor to position a resilient pad in sealing engagement with a stack outlet twelve feet or more above floor level and lock the pad into position and to remove the device, again from ground level, when maintenance has been completed and the engine shut down.