The effects of argon dilution on the translational and rotational temperatures of SiH in both silane and disilane plasmas have been investigated using the imaging of radicals interacting with surfaces (IRIS) technique. The average rotational temperature of SiH determined from the SiH excitation spectra is similar to 500 K in both SiH4/Ar and Si2H6/Ar plasmas, with no obvious dependence on the fraction of argon dilution. Modeling of kinetic data yields average SiH translational temperatures of similar to 1000 K, with no dependence on the fraction of argon in the SiH4/Ar plasmas within the studied range. In the Si2H6/Ar plasmas, however, the translational temperature decreases from similar to 1000 to similar to 550 K as the At fraction in the plasma increases. Thus, at the highest Ar fractions, the translational and rotational temperatures are nearly identical, indicating that the SiH radicals are thermally equilibrated. The underlying chemistry and mechanisms of SiH energy equilibration in Ar-diluted plasmas are discussed.