The cavity region between the rotor and stator relies on hardware seals and purge flow to discourage hot gas path air from being ingested into the unprotected wheel space. However, ingestion can occur due to a combination of disk pumping, periodic vane-blade interactions, and three-dimensional seal geometry effects. These mechanisms create flow instabilities that are detrimental to cavity seal performance under certain conditions. In this paper, a one-stage turbine operating at engine representative conditions was utilized to study the effect of steady and time-resolved under-platform cavity temperatures and pressures across a range of coolant flow rates in the presence of vane trailing edge (VTE) flow. This study correlates time-resolved pressure with time-resolved temperature to identify primary frequencies driving ingestion. At certain flow rates, the time-resolved pressures are out of phase with the temperatures, indicating ingestion. These same flow rates were found to correlate to an inflection region in the cooling effectiveness curve where the maximum amplitude of the time-varying behavior coincides with the cooling effectiveness inflection point. Using a time-accurate computational model, simulations near this inflection region illustrate ingestion of high-swirl VTE flow into the cavity region which creates a buffer in the rim seal between swirled main gas path flow and axially injected purge coolant helping to suppress the amplitude of time-resolved behavior.