This paper examines seven acoustic properties of /s/ in Chilean Spanish (CS) and Salvadoran Spanish (ES). Acoustic measurements from 36 speakers, balanced for gender and dialect, reveal several cross-dialectal differences: CS /s/ was significantly longer than ES /s/ in coda position and had a higher spectral center of gravity. Two findings were mitigated by gender: women in both dialects were more likely to voice /s/, but the magnitude of the difference in voicing between male and female speakers was greater in CS. There were no differences in relative intensity in CS, while in ES, /s/ used by males has significantly lower relative intensity than /s/ used by females. No dialect differences were found for variance, kurtosis, or skewness. While both CS and ES are frequently collocated under the umbrella of "/s/ weakening dialects," our results show that tokens of non-deleted /s/ are acoustically distinct. These findings suggest that shorter duration and lower spectral energy in ES could be the result of a looser or backer constriction of /s/ and may have implications for work examining cross-dialectal differences in /s/ lenition at the phonetics/phonology interface.