We study atom losses associated to a previously unreported magnetic Feshbach resonance in potassium 39. This resonance is peculiar in that it presents $d$-wave character both in the open and in the closed channels, directly coupled by the dominant spin-exchange interaction. The losses associated to a $d$-wave open-channel resonance present specific signatures such as strong temperature dependance and anisotropic line shapes. The resonance strength and position depend on the axial projection of the orbital angular momentum of the system and are extracted from rigorous multichannel calculations. A two-step model, with an intermediate collision complex being ejected from the trap after collisions with free atoms, permits to reproduce the observed dependance of the loss rate as a function of temperature and magnetic field.