This article covers replacing the coolant expansion tank (coolant reservoir) in a BMW E60/E61 5 series and E63/E64 6 series vehicle. Even though we used a 2005 645ci to perform this repair, this article can be applied to any 2004-2010 5 or 6 series vehicle with minor modifications.
A BMW coolant expansion tank replacement in your 2004-2010 5 and 6 series car is an easy repair that can keep you from being stranded on the side of the highway or dealing with a blown cylinder head gasket.
If there is an “Achilles Heel” on older (10 years plus) BMWs, it’s failure of the coolant system…most notably the coolant expansion tank. The coolant expansion tank (also known as the BMW coolant reservoir) is a molded plastic part that is under constant heat and pressure. After years of this abuse, the plastic expansion tank can become brittle and fail. When a BMW coolant reservoir fails you will know it; it is usually a loud bang followed with steam and fluid being ejected from the hood of the car. Not a pretty sight.
If you are on the road and this happens, pull over immediately and shut the vehicle down. Even driving for a short time with a failed coolant tank will result in a blown cylinder head gasket, and the demise of your vehicle (unless you need a parts car parked in your backyard).
The BMW E60/E61 5 series and E63/E64 6 series both use the same coolant expansion tank. The only difference is the 8 cylinder N62 models haave an extra coolant hose attached to the coolant reservoir. We show you both tank configurations in the repair steps below.
Many owners do not wait for failure to perform a BMW coolant expansion tank replacement. In fact, them BMW Repair Guide recommends a BMW coolant expansion tank should be replaced every ten years/100,000 miles for regularly driven vehicles.
1. Coolant expansion tank (required) – We can’t stress enough the need for using a superior OEM quality coolant reservoir in your BMW. Cheap aftermarket tanks have a high failure rate and and can put you at risk for damaging your engine. We give you several options based on your brand preference and budget.
2. Coolant expansion tank cap (required) – Always replace the cap when installing a new coolant reservoir.
3. Coolant/Anti Freeze (required) – You will need to top off your coolant after doing this repair. Only use Genuine BMW Coolant/Anti Freeze mixed 50/50 with distilled water.
- Make sure engine has completely cooled before starting this repair.
- Identify the location of the BMW coolant expansion tank in your vehicle.
- Position a 5 gallon drain pan under coolant expansion tank to catch any spilled coolant.
- Remove the vent hose by using a metal pick to release the metal clip and pulling free from the expansion tank. If hose will not pull off, use a flat blade screwdriver and the palm of your hand and gently push off.
- If working on an 8 cylinder (N62) model, remove the overflow hose using the same technique as in step 4. Six cylinder models do not have an overflow hose.
- Use a T20 torx bit to remove the two BMW coolant expansion tank mounting screws.
- Pull the coolant expansion tank out of engine compartment until you can access the bottom reservoir hose.
- Remove the reservoir hose using the same technique as in steps 4 and 5 above.
- Remove the fluid level sensor electrical connection on bottom of expansion tank.
- Remove the BMW coolant expansion tank from the vehicle.
- Install new coolant expansion tank using the reverse steps above.
- Fill reservoir with fresh coolant, replace cap, and start engine. Allow coolant to circulate through engine for a couple of minutes. Turn off engine, remove cap, and top off coolant if necessary. Only use Genuine BMW coolant/antifreeze mixed 50/50 with distilled water.
The Repair Difficulty Level displays graphically how challenging the repair is, from easy to advanced. Easy repairs usually require very few tools, have short repair times and do not require jacking and supporting the vehicle. As the difficulty level rises, expect the repair to demand more time, specialized tools, and better understanding of mechanics to complete the job.