The majority of aircraft were fitted with a car-type radiator mounted in the aircraft's nose; two different variants were used, a more common rounded-top model and a more angular flat-top unit. Alternatively, some D.Is were provided with a twin-block radiator mounted one above the other on the forward fuselage, which enabled a more nose to be adopted. Regardless of the version of the radiator used, cooling was a persistent issue suffered by the type. As a result, many D.Is would be flown with the engine cowling being completely removed by ground crews; a solution to the overheating issue was fitted on later-built aircraft in the form of a simple low-cut fringe cowl that kept the engine cylinders exposed and an elongated block radiator fixed onto the leading edge of the wing.