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Subject: DIY: Radiator expansion tank replacement procedure Author: DavidC (moderator) : member since December, 2003 : 12931 posts Posted on: 2005-01-07 19:58:38

Following up on my recently demised radiator expansion tank failure (see 'Check Coolant' warning and overheating today on the highway.), here are the steps involved in removing and replacing the expansion tank on a '97 740iL.


It's easier to work on the expansion tank with the air filter box out of the way. Pop the four retaining clips on the air filter box and set the lid aside.


Then remove the 13mm hex bolt holding the lower half of the air box to the car body. Slide the flexible air intake tube away from the body and lift the box out of the car.


Disconnect the plastic electrical connector for the coolant level sensor at the bottom of the expansion tank.


Loosen the 6mm hose clamp on the coolant hose at the lower side of the expansion tank.


And put a stopper in the hose to prevent coolant from leaking out. In my case the expansion tank had already leaked most of its contents so there was only a small amount of coolant in the hose. Remember that antifreeze is deadly to your pets. They like to drink it because it evidently tastes sweet, so clean up everything on the floor to keep them safe.



Use two small flat-blade screwdrivers to press in on the tabs of the plastic retaining clip around the vent screw. It’s easier to remove the vent screw first.


Don't forget to retain the O-ring with the vent screw.


Now the expansion tank can be leaned back slightly to reveal the vent hose.


Remove the two plastic rivets that at the top of the fan cover (see arrows in the photo above). The fan cover can then be lifted up for easier access to the vent hose and its hose clamp. After removing the vent tube hose clamp, lift the expansion tank up and out of the engine bay.



Here's where my expansion tank cracked and leaked fluid. It was on the side facing the radiator, so the source of the leak wasn't obvious until the tank was actually removed from the car.


Here's a photo of the coolant level sensor. I had to replace mine because one of the two plastic tabs was broken. It just twists into the bottom of the expansion tank.


The original clamp on the vent hose wasn't designed to be re-used, so I replaced it with a standard 5/8-inch hose clamp.


The new expansion tank (part # 17111741167) has a different size thread than the old one, so I had to replace the cap (part # 17111742231) as well.

Put everything back together in the reverse order then fill with coolant. If you don't use the BMW brand coolant ($16/gallon at the dealer), choose one that's phosphate-free and safe for aluminum, such as Peake.

The cost of this project was $67 for the expansion tank and $24 for the radiator cap, plus 2 gallons of antifreeze.

David Cecil
Lexington, KY
Titanium silver '01 750iL, 92k miles
Oxford green '97 740iL, 184k miles
Alpine white '92 750iL, 95k miles (for sale)
Charcoal gray '86 735i, 101k miles (for sale)

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The 7 Series E38 Forum | Message Thread:

• DIY: Radiator expansion tank replacement procedure (pic) (url) - DavidC 2005-01-07 19:58:38 (79974 views)
  • Re: DIY: Radiator expansion tank replacement procedure - admills 2005-07-11 23:09:18 (3822 views)
  • Here are the part numbers (url) - DavidC 2005-01-14 04:18:30 (2996 views)
  • Thanks! - thesteve 2005-01-07 21:26:20 (1602 views)
  • Don't forget to bleed the system at the EntLuftung screw - ChicagoE38 2005-01-07 20:25:38 (10409 views)
    • yes, good point (nt) - DavidC 2005-01-07 20:49:15 (2481 views)

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