This paper focuses on the transient thermal signal around an engine cylinder in order to propose a new and non-intrusive method of knock detection. Numerical simulations of unsteady heat transfer through the cylinder and inside the coolant flow are performed. The amplification of wall heat transfer due to knock is taken into account by a self-developed program. It enables one to fix the instantaneous heat flux on the internal side of the cylinder. The transient component of the thermal signal is then calculated and analysed. The effect of a machining, consisting of a transverse groove, which reduces the cylinder liner thermal resistance, is investigated. This groove disturbs the turbulent coolant flow, and its shape mainly influences the heat transfer from the wall to the fluid. The numerical results show that the use of a square groove would multiply by three the amplitude of the transient thermal signal recorded within the water compared to a smooth wall case. Moreover, the amplitude can be enhanced by using a nanofluid as coolant because of its higher thermal diffusivity. (c) 2005 Elsevier Ltd. All rights reserved.