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Coolant Expansion Tank Replacement
 
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Pelican Technical Article:

Coolant Expansion Tank Replacement

Nick Czerula

Time:

2 hours2 hrs

Tab:

$200

Talent:

**

Tools:

Set of sockets, wrenches, screwdrivers

Applicable Models:

BMW X3 Sport Utility (2004-06)

Parts Required:

Expansion tank, radiator hoses, engine coolant

Hot Tip:

Work with a cool engine

Performance Gain:

Car will cool down again, coolant leak repaired

Complementary Modification:

Change radiator hoses, Expansion tank mounting bracket, flush cooling system

Maintaining the cooling system so that the engine does not overheat is a significant step toward getting engine longevity. There are many components in the BMW X3 cooling system:

  • Radiator and coolant reservoir tank.
  • Belt driven coolant pump bolted to the front of the engine block.
  • Electric cooling fan attached to front of radiator. The cooling fan is controlled by the engine control module (ECM) via an output final stage.
  • Thermostat.
  • Automatic transmission cooler or heat exchanger (if equipped).
  • Heater valve and heater core (for climate control).
  • Coolant level sensor inside expansion tank.
  • Coolant temperature sensor at cylinder head.
  • Radiator outlet temperature sensor
  • Coolant hoses and lines.

When a coolant expansion tank (reservoir) ages it becomes brittle and develops hairline cracks. Inspect your expansion tank every time you change your oil. Look for cracks or any signs of leaks. Ignoring a small crack is a bad idea as they can grow rapidly and create a major coolant leak before you know it. The coolant level sensor is located in the bottom of the tank. If you have a low coolant level message, but your coolant level is OK, you may have a faulty sensor. In this tech article I will show you how to replace the expansion tank and test and replace the coolant level sensor.

Do not remove the expansion tank cap while the engine is hot. Coolant or hot steam may escape and will scald you. To do any work on the cooling system, wait until the engine has cooled off.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Drain the cooling system. See our tech article on draining and replacing your coolant.

When a coolant expansion tank (reservoir) (red arrow) ages it becomes brittle and develops hairline cracks.
Figure 1

When a coolant expansion tank (reservoir) (red arrow) ages it becomes brittle and develops hairline cracks. Inspect your expansion tank every time you change your oil. Look for cracks or any signs of leaks. The coolant level sensor is located in the bottom of the tank.

Start by removing the four T25 Torx fasteners (red arrows) for the fresh air intake duct.
Figure 2

Start by removing the four T25 Torx fasteners (red arrows) for the fresh air intake duct. Next you will unclip the five air filter housing retaining clips. Lift them up and unhook from the lid of the intake air housing. Start with the two near the mass air flow sensor. Then release the front clips.

Once you release all the clips, lift the intake air duct (blue arrow) and pull it out of the air filter housing lid (red arrow) then remove it from the radiator support.
Figure 3

Once you release all the clips, lift the intake air duct (blue arrow) and pull it out of the air filter housing lid (red arrow) then remove it from the radiator support.

Next, remove the cooling fan (red arrow).
Figure 4

Next, remove the cooling fan (red arrow). See our tech article on radiator cooling fan replacing.

Working at the thermostat, use a flathead screwdriver to lift the hose spring locks (red arrow) up until they stop.
Figure 5

Working at the thermostat, use a flathead screwdriver to lift the hose spring locks (red arrow) up until they stop.

Pull the hose (red arrow) off the thermostat toward the left side.
Figure 6

Pull the hose (red arrow) off the thermostat toward the left side. If the hose is stuck, wiggle it up and down as you pull it off. Work gently.

Working at the top of coolant expansion tank, use a flathead screwdriver, release both upper hose clips by prying them up (red arrows).
Figure 7

Working at the top of coolant expansion tank, use a flathead screwdriver, release both upper hose clips by prying them up (red arrows). Next, remove the upper hose from the coolant expansion tank by pulling it straight off. You may have to wiggle the hose a bit to get it to move free. Be careful not to damage the hose or tank as both are made of plastic.

Inspect the hose O-rings (red arrow).
Figure 8

Inspect the hose O-rings (red arrow). If flat or worn, replace the hoses.

Working at the bottom of coolant expansion tank, using a flathead screwdriver, release the lower hose retaining clip by it prying up (red arrow).
Figure 9

Working at the bottom of coolant expansion tank, using a flathead screwdriver, release the lower hose retaining clip by it prying up (red arrow). Then disconnect the hose by pulling it off the coolant expansion tank fitting.

Follow the lower hose to the rubber mount on the body (red arrow).
Figure 10

Follow the lower hose to the rubber mount on the body (red arrow). Unclip the rubber mount and set hose aside.

Working at lower right side of the coolant expansion tank, locate the coolant expansion tank release tab (red arrows).
Figure 11

Working at lower right side of the coolant expansion tank, locate the coolant expansion tank release tab (red arrows). Pull the retaining clip tab out in order to release the bottom of the expansion tank from the mounting bracket (red arrows).

Once you release the retainer clip, the expansion tank can be removed by pulling it up and off the radiator mounting bracket.
Figure 12

Once you release the retainer clip, the expansion tank can be removed by pulling it up and off the radiator mounting bracket. It may stick and give you a hard time. If this is the case, gently pry between the expansion tank and mounting bracket to release. Be very careful, all items you are prying on are made of plastic.

Working at the bottom of the coolant tank, disconnect the coolant level sensor electrical connector by pressing the tab (red arrow) and pulling the connector straight off.
Figure 13

Working at the bottom of the coolant tank, disconnect the coolant level sensor electrical connector by pressing the tab (red arrow) and pulling the connector straight off. Then remove the expansion tank from the vehicle.

When replacing the expansion tank, you will have to swap the coolant level sensor from the old tank to the new one.
Figure 14

When replacing the expansion tank, you will have to swap the coolant level sensor from the old tank to the new one. Rotate the coolant level sensor 90 degrees counter-clockwise and pull out (red arrow). Note the silicone sealant on my sensor. This is a sign of a shoddy repair and the cause of the leak I was chasing.

The expansion tank mounting bracket has an integrated thermostat for the ATF heat exchanger.
Figure 15

The expansion tank mounting bracket has an integrated thermostat for the ATF heat exchanger. It is very common for this part to break during expansion tank removal. If it does, you will have to replace the thermostat. Pop the old one out and snap the new one into place. When installing your new expansion tank, connect the coolant level sensor electrical connector, then press it into the mounting bracket and engage the retaining clip. Next, connect the lower hose to the expansion tank; the retaining clip is properly seated when an audible click is heard. Connect the upper hose and engage the retaining clips until an audible click is heard. Reverse remaining steps. Fill and bleed the cooling system. Once complete, double check all hose connections and check the engine for coolant leaks.

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Page last updated: Fri 3/24/2017 03:12:34 AM