Toluene was seeded homogeneously into the intake gas. Fluorescence was excited at 248 nm and detected spectrally integrated. Toluene fluorescence decreases strongly with increasing temperature. Estimating the absolute in-cylinder temperature from isentropic compression along the measured pressure trace, we found the magnitude of this decrease in the engine to be consistent with literature data from heated flow-cell measurements. This calibration allowed for determination of the spatial fluctuations in temperature against the multi-cycle average temperature. Precision error, mostly from laser mode fluctuations, was between 1.6 and 4.0 K depending on crank angle.