Replace Coolant Expansion Tank and Flush and Fill Coolant

The quickest way to be scorned by the E28 community is to post pictures of your engine with an old, yellow coolant expansion tank. Replacing it was a no-brainer, but the part is specific to the M5 and is not cheap ($135). I multitasked when the car was up for the front suspension overhaul.

With the age of the coolant unknown, I decided to flush the existing coolant. Not wanting to use tap water, I went through a lot of distilled water to flush the coolant as much as I could front the block. Removing the drain plug from the block resulted in an uncontrollable deluge and a bit of a mess.

I put a new washer on the plug and reinstalled it. I replaced the expansion tank and then filled with a 50/50 solution of distilled water and Genuine BMW coolant (blue). As always, the internet offered both insight and controversy on the correct proportions and on the use of water wetter. I decided to just go for it.

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