I attempted to do a cooling system flush today (along with replacement of radiator hoses, water pump and thermostat).

After removing the blue drain plug (my car only had one, apparently some cars have two) on the bottom of the radiator and another drain plug on the side of the engine under the exhaust manifold, my expansion tank still has a bunch of coolant left in it.

Does any one know if that's normal? Is there another special way I should get it out?

  • Thanks for the responses, guys. The reason why this was a bit confusing is because on this car expansion tank is not as separate from the rest of the cooling system as you'd expect. It is mounted right on the radiator and is actually an active part of the coolant circulation. See: realoem.com/bmw/… Drain plug is almost directly under the expansion tank, so I kinda expected that it would just drain on this car.
    – DXM
    Commented May 5, 2011 at 23:57

3 Answers 3


That is normal. I wouldn't worry about trying to get the rest of it out.


Is there another special way I should get it out?

You should be able to siphon out the expansion tank if you'd really like everything to be totally empty.

Reminder: coolant is toxic. Do not attempt the "suck the hose" method to start the siphon.


Just did a coolant change on the other half's 330i and had the same problem. Hers is fitted with an oil cooler at the bottom of the expansion tank, just push a small clip up and remove oil cooler,and this will drain tank

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