I am not familiar with this dash at all, but most are similar at least generally. Locate the back of the temp gauge, see how it is attached to the cluster, i.e. nuts/studs or electrical connectors. See if anything is loose and tighten accordingly. Could also be connector for temp sensor, but those are mostly either on or off the clips. Hope this helps. Maybe Steve or Donnie have experience with setup. If they do, I'm sure they'll help you out.
1987 BMW 325