Coolant Flush and Replacement – BMW B46/B48 Turbo 4 Cylinder Engine
Step 1 - Purchase Parts
Antifreeze/Coolant
This is the same factory coolant that would be installed at the dealership. Aftermarket coolants actually cost more than Genuine BMW...so why would you use them? Mixed 50/50 with distilled water, this container makes 2 gallons of factory coolant.
Coolant Vacuum Fill Tool
Whether you are a home mechanic or shop professional, there is only one way to properly refill the coolant system on a BMW - with a vacuum fill tool. This inexpensive tool easily attaches to the expansion tank creating a vacuum that "sucks" the coolant into system, virtually eliminating any air pockets that could cause engine overheating. Never try and refill your coolant system without one.
Drain Pan 15 qt
The best oil and coolant drain pans do the following: catch the fluids without spilling and store them in a container that can be easily taken to the recycling center for dumping. This fantastic 15 qt drain pan does both. Not only is it low enough to slip easily under your vehicle, but it seals tightly so you can take the fluids to a responsible recycling facility without spilling in your vehicle.
Step 2 - Repair Procedure
There are two separate cooling systems in the B46/B48 engine that have to be drained - the high temperature and the low temperature coolings systems.
Before starting this repair, make sure you have a suitable drain pan ready to capture the coolant. Please see our parts and supplies list above if you need to purchase one.
- Remove the front under body protection cover (3) from the vehicle by removing the screws (1) and (2).
- Remove the cap from the high temperature expansion tank (1)
- The high temperature coolant system is drained from the bottom left of the radiator.
- Position a drain pan under the coolant hose and remove it from the radiator. Allow the system to thoroughly drain.
- Replace the radiator hose.
- Remove the cap from the low temperature expansion tank (1)
- In order to drain the low temperature coolant, the trim inside the right front wheel well must be loosened and the right lower cover removed. This must be done so the coolant pipe on the right side of the radiator can be accessed.
- Begin by removing the two screws (1) securing the right wheel housing trim as shown in the image.
- Next, remove the screws (1) anchoring the right lower cover to the front number. Remove the cover from the vehicle.
- Locate the right coolant hose attached to the right side of the radiator. Place a drain pan underneath it.
- Disconnect the coolant hose from the radiator and thoroughly drain the system. Replace the hose.
- The high and low temperature cooling systems must be refilled with coolant using a vacuum refill tool. The vacuum refill tool is inexpensive and should be a standard item in every home mechanic's or professional repair shop's tool box. Please see our parts block to order a vacuum refill tool if you do not have one.
- Never attempt to refill the coolant system without the vacuum refill tool. It will leave air pockets that could potentially cause engine overheating.
Please watch the following video to learn how to properly use the coolant vacuum refill tool. This procedure must be repeated for both the low and high temperature cooling systems!
The B46/B48 engine has an automated bleeding process that takes approximately 12 minutes.
Initiating the automatic bleeding process.
- (Optional Hook a battery charger to the vehicle. Since the bleeding process takes 12 minutes, it may run down the battery to a point where the vehicle can't be started.
- Turn the ignition on (do not start vehicle).
- Turn on the low-beam headlights and hazard warning lights. If these lights are not turned on, the ignition will shut itself off before the bleeding process is done!
- Verify the vehicle is not set to ECO PRO.
- Set the heater to maximum temperature and the blower to its lowest setting.
- Depress the accelerator pedal all the way to the floor for 10 seconds then release.
- The automated bleeding process has been initiated. You can verify by listening for a humming sound coming from the water pump.
- The bleeding process takes approximately 12 minutes. When it is finished, top off the coolant and secure the expansion tank cap.