Coolant Expansion Tank Replacement DIY
This is the procedure I followed to successfully replace a leaking coolant expansion tank on my 2004 4.4 X5 with 60-70k miles. I would rate this as a relatively easy do-it-yourself project. It’s somewhere between replacing wiper blades and replacing brake pads. I spent 20 minutes doing it. I could do it in 10 minutes or less a second time.
I started seeing the coolant low warning message. The tank is located between the headlight and the wheel well on the left side (driver side in US). It has a black screw-on cap. I topped it off with distilled water when it was cooled off. I knew there was a problem when it started to occur more often. I could see a white coolant residue stain next to the tank on the wheel well and on various parts between the tank and the engine. The top of the tank was clean. See figure 1 for a side view of a new and leaking tank.
Parts & Tools
I ordered a new tank ($75), cap ($12) and a gallon of BMW coolant ($19) online from Bavarian Autosport. I used a pair of pliers, a long screw driver, a rubber mallet and a 10mm socket and ratchet.
Unless you are a glutton for punishment, I recommend doing this when the engine is cool. Loosen the cap on the tank to release any pressure. There are three hoses, an electrical connection and two 10mm nuts to remove.
The hose connections consist of the hose attached to a plastic fitting with a hose clamp. You do not need to touch the hose clamp. The plastic fitting is held onto the tank with a clever wire clip locking mechanism. The top of the clip extends above the plastic fitting. Pull the wire clip straight up with pliers. Then you can pull the plastic fitting and hose away from the tank. The plastic fitting might need some “gentle encouragement” from the screw driver and rubber mallet to separate it from the tank.
Two hoses are near the top of the tank. This is a good place to start because they are easy to see and access. Next, remove the hose near the bottom of the tank on the side closest to the engine. Any coolant in the tank will start to leak out at this point. I stuffed a wad of paper towel into the tank side of the connection when I pulled the hose off. You might want to pre-position a rag under the tank to catch any coolant before removing the hose. Or you could use the yellow plastic plug from the new tank.
The electrical connection is on the bottom of the tank. Remove the two nuts holding the top of the tank to the bracket behind the headlight. Now pull the tank up. It won’t come all the way out because of the length of the wire. Feed any excess wire through so you can pull the tank high enough to see the connection on the bottom. The tank side of the connection exits the bottom of the tank and runs parallel to the bottom of the tank toward the wheel well. There is a rocker on the connection, facing away from the tank, that releases the lock. Push down on the end closest to the wire end of the connection to release it while pulling the wire side of the connection away from the tank side of the connection and parallel to the bottom of the tank.
I cleaned all the hose and electrical connections. Then I retraced my steps in reverse order. I attached the electrical connection to the new tank, bolted the tank back in place, attached the lower hose and attached the two upper hoses. There is a plastic post extending from the bottom of the tank. This fits into a rubber grommet in the bottom of the bracket. Slide the hose connections onto the fittings on the tank. Then use the pliers to slide the wire clip back down into the groove. There is a matching groove in the tank side of the connection. If the connections were aligned properly when you slide the wire back down then you will not be able to pull the hose back off by hand. Once the tank was in place with all the connections, I filled the tank with straight coolant.
I drove to the local self-service car wash and power washed the engine compartment. I checked the coolant level in the tank a few hours after I returned home and topped it off. I repeated the drive, cool off and top off routine again. I checked the coolant first thing in the morning for a few days to make sure it wasn’t leaking. It worked like a charm!
I’d like to thank everyone who has posted DIY instructions. I’ve saved a lot of money and enjoyed the projects as a result. I hope this returns the favor in some small way.
Figure 1 – Side view of new tank on left, leaking tank on right
Note that the top of the leaking tank is clean.
Figure 2 – Hose connection left to right: tank, plastic connector with wire clip and hose with hose clamp
Note the wire clip rides in a groove in the plastic connector. Pull up on the wire in between the two plastic ears to release the lock.
Figure 3 – Bottom view of the electrical connection
Note the part in the middle on the right with a groove in it. This is where you apply pressure to release the lock.