Start hwinfo64.exe and start logging (bottom right) then start the Sims 4. After it crashes stop logging find the log file and look for the latest CPU and GPU temperatures recorded.
@OxfordGirl I just want to say that if you're not sure what you're looking at in the log file, you can upload it here for us to look at instead. You'll need to use a third-party filehosting site (Google Drive, Dropbox, etc.), and please either leave the log in .csv format or create a .zip file.