2005 BMW 325i coolant temperature gauge

About two months ago I noticed a small puddle of coolant and foolishly added coolant without remembering to BLEED the system while I added coolant. I located the source of the leak (the coolant sensor located on the lower radiator hose) and concluded problem solved. Wrong. Ever since adding coolant, I have noticed the coolant temperature gauge no longer remains in the middle (twelve o’clock) position and instead stays in the blue (“cool”) range. I have bled the system multiple times and replaced the new sensor temporarily with the old sensor, believing perhaps the new sensor was defective. Heat can be intermittent but is generally present. Coolant temperature gauge needle moves to center if I let car idle but will move to left when I drive. Top radiator hose is HOT to the touch. So…faulty thermostat stuck in open position or stubborn air present in system? And, yes, I checked OBD and no codes as of last week. I will gladly replace thermostat but would hate to do the job if it is not necessary.

When temperature regulation is an issue, the T-stat is always a good place to start.
When bleeding the system of air, there are two key elements to remember:

  1. air migrates to th ehighest point, usually the fill cap but in some cars with a higher point built in there’ll be a purge valve.
  2. it’s important when purging air to have the heat on. On most modern cars there’ll be a valve in the heater hose going to the heater core, and unless this is opened the core will not purge properly.

Try a new T-stat and post back.