The following article provides detailed instructions on performing a thermostat replacement on a BMW E46 3 series car. Even though we have used a 2003 BMW 325ci to perform this installation, this article can be applied to any E46 3 series vehicle, including the 323i, 328i and 330i coupe, sedan and convertible.
The BMW E46 thermostat is an important component of the 3 series’ cooling system and is prone to leaking and failure.
The BMW E46 thermostat is an integral part of the car’s cooling system. Its main function is controlling the amount of coolant flowing into the engine block from the vehicle’s radiator. When the BMW E46 engine is running “cold”, the thermostat remains closed blocking coolant from circulating through the engine block. As the motor slowly heats up, the thermostat opens allowing fluid to travel in which prevents the engine from overheating.
The thermostat is effectively a valve that opens and closes depending on the temperature of the engine. It allows the engine to warm up correctly and prevents premature wear of critical parts in your vehicle’s power plant. If coolant was allowed to flow through a cold engine, the motor would struggle to reach operating temperature and would not run efficiently. Indications that your BMW E46 thermostat has failed include the engine struggling to reach operating temperature and erratic changes in the temperature gauge. The BMW E46 thermostat has a “fail safe” mechanism that keeps it in the open position if it completely shuts down, so engine overheating is usually not associated with thermostat failure in this model 3 series.
The BMW E46 thermostat is located inside a plastic housing on the front of the engine. The plastic housing has its own set of known issues including leaking from cracks and old gaskets. The brutal heat conditions inside the E46 engine can cause the plastic thermostat housing to fracture over time, allowing coolant to leak out. The thermostat housing gasket is also susceptible to heat and age, causing it to become brittle and allowing fluid to escape. A typical sign of a leaking thermostat housing is a pool of coolant under the engine of the car, especially after it has warmed up. A leaking thermostat housing should be replaced immediately to avoid loss of coolant and possible engine overheating.
The BMW E46 thermostat and housing is normally purchased as one unit. The BMW Repair Guide does not recommend replacing one without the other.
1. Thermostat (required) – The thermostat and housing for the BMW E46 3 series come as one unit. Always use a high quality replacement from a reputable manufacturer…we give you several excellent choices based on your budget.
2. Engine coolant (required) – Expect to lose a about 1/2 gallon of coolant when doing this repair. Only replace the coolant in your BMW E46 with Genuine BMW Antifreeze/Coolant mixed 50/50 with distilled water (from you local grocery store).
3. Upper radiator hose (optional) – The upper radiator hose runs from the thermostat to the coolant reservoir. It is a common source of leaks and cooling system failures in the BMW E46. Since the upper radiator hose will have to be removed to complete this repair, now is a great time to replace if it is getting old. Choose from one of these excellent manufacturers.
4. Lower radiator hose (optional) – The lower radiator hose runs from the thermostat to the bottom of the radiator, and is another source of potential cooling system failure. Now is an excellent time to replace this hose if it is getting old or worn. We give you several quality options to choose from.
Removing the old thermostat from your BMW E46 is a relatively simple procedure that can be done in less than an hour.
- Jack and support the front of the car. Not sure how to jack and support your E46? See our article BMW Jacking and Supporting for Repairs and Maintenance.
- If the belly pan (aka – skid plate or lower engine cover) is still installed on your vehicle, remove it using an 8mm nut driver. Belly pans tend to disappear on older BMWs – they take a lot of abuse and are one of those parts that owners just don’t spend money on replacing. The belly pan needs to be removed because the coolant system needs to be drained.
- Moving to the engine compartment, disconnect the mass air flow (MAF) sensor.
- Using a flat blade screwdriver, loosen the hose clamp on the intake boot.
- Unlatch the four clamps on the lid of the intake muffler. Note that one of the clamps is difficult to get to…use a metal pick to release if you can’t reach it with your fingers. Remove the lid from the vehicle.
- Using a 10mm socket wrench, remove the two intake muffler mounting bolts. Remove the intake muffler from the engine compartment.
- Remove the plastic air intake tube.
- Use a trim removal tool to remove the three plastics rivets anchoring the air intake tube to the frame of the vehicle. Remove the intake tube from the vehicle.
- Remove the air quality sensor and the wiring harness connector from the fan shroud and safely tuck out of the way.
- Position a 5 gallon drain pan under the front of the vehicle.
- Release the clips securing the upper radiator hose to the thermostat housing and the expansion tank. Remove the hose from the engine. The hose must be removed so you can gain clear access to the cooling fan clutch nut.
- Don’t try and remove the fan shroud yet…it is easier to remove with the cooling fan and fan clutch. There is also less chance of breaking the fan shroud if you remove it with the cooling fan.
- Next, the infamous cooling fan and fan clutch must be removed from the water pump pulley. If the nut on the fan clutch is seized and cannot be removed from the water pump pulley with the special fan clutch removal tool (which is a very common occurrence), then you will have to unbolt and remove the cooling fan from the clutch. Remember the fan clutch nut is a reverse thread…you must turn it clockwise to loosen it.
- The first step in all of this is to try and remove the fan clutch from the pulley with the special fan clutch removal tool. Place the fan clutch tool on the pulley and the clutch nut as shown in the following image. Remember the fan clutch nut is a reverse thread…you must turn it clockwise to loosen it.
- The nut is a reverse thread…this means you must turn the nut CLOCKWISE to remove it (you would be surprised how many mechanics will still try and turn it the other direction…even after all of our obnoxious reminders).
- If you can loosen the nut, then spin the fan clutch nut off of the pulley. If the nut is seized and cannot be removed, then you will need to follow additional steps below to remove the cooling fan blades. Either way, proceed to the next step #17.
- Remove the right T27 torx radiator anchor screw. This screw also anchors the fan shroud to the radiator. The right side of the fan shroud is anchored to the radiator with a plastic rivet. Remove the rivet with a trim removal tool.
- If you were able to remove the fan clutch from the water pump pulley, grasp the shroud and the cooling fan and slowly remove them from the engine compartment together and proceed to step 21. If the nut was seized and you could not remove the fan, proceed to the next step #19.
- If the clutch nut is frozen and you could not loosen it, slowly pull the shroud up and out of the front of the vehicle around the cooling fan. Don’t pull on it if it gets hung up…you may have to get under the front of the car to help guide it behind the fan blades. Take your time and do your best to get it out with minimal damage to the shroud.
- Use a T30 torx bit to remove the three fan clutch mounting bolts. Remove the cooling fan from the vehicle.
- You now have clear access to the thermostat housing. Start by removing the lower radiator hose that runs from the right side of the thermostat to the bottom of the radiator. Release the metal clip and pull it free…make sure you have a drain pan under it to catch any coolant.
- Next, remove the thermostat temperature sensor connection.
- The thermostat housing is anchored to the front of the engine with four bolts. Three of the bolts are 10mm and one is 13mm. If you were not able to remove the fan clutch in step 13 above, the bottom two can be a bit of a challenge to get out. Use patience when removing them.
- Grasp the thermostat housing and pull it loose from the front of the engine. Remove the housing from the car.
Installing the new thermostat is a very simple procedure. It is very important that the surface of the engine is thoroughly cleaned where the new thermostat mounts; any oil, grease or debris can affect the thermostat gasket’s ability to seal and create a leak. It is also very important to add a multipurpose grease to the fan clutch nut to prevent it from seizing in the future.
- Use CRC Brakleen to thoroughly clean the engine where the thermostat housing mounts. Make sure to get all of the dirt, oil and grime off. Not cleaning it thoroughly could prevent the new gasket from sealing correctly and may create future leaks.
- Unpack the new thermostat. Verify you have the correct part number.
- Verify your new thermostat comes with a gasket; usually they are already pre-installed in the housing. If the gasket is not pre-installed or you purchased the thermostat and gasket separately, install the new thermostat gasket in the thermostat housing. Make sure it is seated correctly so it doesn’t get pinched during installation.
- Install the new thermostat housing on the front of the engine and finger tighten the four mounting bolts. Torque the mounting bolts to 10Nm (7.5 ft-lb).
- Close the locking clip on the lower radiator hose then mount onto the thermostat housing. Push on the hose until you hear it click into its locked position.
- If you had to remove your cooling fan from the clutch because of a seized nut, reinstall it using the three torx mounting bolts. Make sure you have the fan blades facing the correct direction. Torque the mounting bolts to 10 Nm (7.5 ft-lb).
- If you were able to remove your cooling fan using the fan clutch tool, liberally apply some multipurpose automotive grease to the clutch nut threads. This will prevent it from seizing up in the future and make it easy to remove for future repairs.
- Lower the fan shroud and the cooling fan together into the front of the vehicle. Spin the cooling fan onto the water pump counterclockwise to tighten. Use the special fan clutch tool to tighten the nut as snug as you can get it. Since it is a reverse thread, it is self tightening so you do not have to worry about torquing it.
- Reinstall the fan shroud mounting fasteners, the air quality sensor and the wiring harness connection.
- Install the upper radiator hose back onto the thermostat and the coolant expansion tank.
- Reinstall the intake tube, intake muffler and the MAF sensor.
- Reinstall the belly pan under the engine.
Refilling and bleeding the coolant system in your BMW E46 3 series car is a very simple procedure. The goal is to remove any air bubbles trapped in the coolant line that could potentially cause the engine to overheat. Unlike many other repair articles, the BMW Repair Guide uses the “double bleed” approach on their BMW E46 3 series cars. This is a proven method that we have used for years with 100% success. The double bleed method entails purging the air out of the coolant system twice; once with the engine off, and then again with the engine running. We have found this to be the most complete method of removing all of the air out of the E46 cooling system.
- Only use Genuine BMW Antifreeze/Coolant mixed 50/50 with distilled water in your vehicle. Using any other brand of antifreeze/coolant in your BMW is strongly discouraged. Genuine BMW Antifreeze/Coolant was specifically engineered for your BMW…other brands may not cool your engine correctly.
- Loosen the bleed screw on the upper coolant hose.
- Turn the ignition on. Do not start the vehicle.
- Set the HVAC temperature controls to full warm and the fan speed to its lowest setting (this opens the heater core and activates the secondary electric coolant pump).
- Slowly fill the expansion tank with coolant until it starts to spill from the bleeder screw.
- When the coolant spilling from the bleed screw is free of air bubbles (just a steady stream of coolant), tighten the screw and replace the expansion tank cap.
- Start the engine.
- With the engine running, loosen the bleeder screw again. You should get more air bubbles coming out until there is a steady stream of coolant being pushed out of the bleeder hole. Tighten the bleeder screw.
- Allow engine to reach operating temperature (about 5 minutes if cold). Keep an eye on the engine temperature gauge…the needle should stay right in the middle. Check all of the hoses for leaks.
- Allow the engine to cool down. Recheck the coolant level in the expansion tank and top off if necessary.