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BMW E90 Thermostat Replacement DIY 325xi, 328xi, 330xi

In this article I will show you how to change the thermostat on your 2006-2011 BMW 325, 328 or 330.  The job was done on a 2007 328xi, 2WD cars will have a different sub frame that actually allows more access to the thermostat.  Thermostats in E90 3-series BMWs are computer controlled, there is a heating element inside the thermostat that ECU can turn on causing the thermostat to open.  When the thermostat goes out on E90, it is common to get a check engine light with P0128 "Thermostat Stuck Open" code.  All you need for this job is a new thermostat and a gallon of undiluted BMW coolant.

1.  Remove all of the under paneling and drain the coolant from the radiator.

BMW E90 Draining the Coolant

2.  Unclip the electrical connector from the thermostat.

BMW E90 Disconnecting Thermostat Electrical Connector

3.  E90 Thermostat has 4 hoses attached to it.  Two hoses on the front of the thermostat clip on and two in the back are standard hoses with regular hose clamps  Unclip the large hose at the front of the thermostat and pull it off.  There will be some coolant spilling out of that hose so have a pan ready to catch anything that spills out.  When of the coolant drains out, unclip the smaller hose at top of the thermostat.

BMW E90 Disconnecting Thermostat Coolant Hoses

4.  Now you will need to disconnect the two hoses at the back of the thermostat.  One of the hose clamps can be reached from the button of the car with a long screwdriver, the other one can be reached from the top. 

BMW E90 Disconnecting Thermostat Rear Coolant Hoses

5.  The thermostat in E90 is bolted on to the electric water pump.  On Xi models the design of the subframe makes it hard to reach the bolts but it is definitely doable without removing anything extra.  If you are having a really hard time getting to the bolts you can remove the sway bar for more clearance. 

BMW E90 Unbolting Thermostat from Water Pump

6.  New thermostats are made of plastic for whatever reason but so far we haven't seen any come back for warranty.

BMW E90 Original vs New Thermostat Comparison

7.  Put everything back together in the reverse order.  A proper coolant bleeding procedure must be followed to get any trapped air out of the cooling system prior to starting the car.

  • Fill the cooling system with coolant until the expansion tank is full and close the expansion tank cap.
  • Hook up a battery charger to the car or at least turn off the headlights and the radio.
  • Set the heater to the maximum temperature and the fan speed to the lowest.
  • Press the gas pedal to the floor for about 10 seconds.
  • Release the gas pedal and you will near the water pump turn on.
  • Loosen the expansion tank bleeder screw to bleed out the air.  Close it once you get a steady flow of coolant with no air bubbles.
  • The bleeding procedure takes about 12 minutes and once the car is done check the coolant level and add coolant if necessary.
  • Start the car, make sure there are no leaks and reinstall the underpanel.
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