Hi,
Since my car is at 127XXX miles I decided to change the expansion tank since I did not see it on the maintenance history. I had done the cooling system overhaul except for the tank. Since the expansion tank from the e46 was the same as the Z4's i thought. I ordered a Behr expansion tank( part # 376755111) for my 03 Z4 3.0i. I took out the old expansion tank and inspected for any hairline cracks with a magnifying glass. No cracks but I did not want to take a chance so when I was putting the new tank in the bottom of the tank does not push into place for the part that has the tank drain plug. It fits on my old expansion tank but I could not get it in all the way on the new expansion tank . Any solutions? I got my Behr tank for $24.99 off RockAuto and its too late to return it. Am I forced to order a new one? It would cost $38.
When replacing the plastic expansion tank I would replace the plastic mounting plate and assorted hardware that goes along with it. I would only use factory BMW parts for this and look up the parts per your vin number, use reloem.com.
I recently had this exact problem, except mine seated well enough that I wasn’t leaking until the car got nice and warm as I was driving up a hill. Lost all my fluid and overheated, that was fun.
Turns out the expansion is really hard to seat properly. I would strongly recommend taking out the mounting plate that it attaches to out of the engine bay (it was only like 3 bolts) and attaching the tank/clip out of the car. I had to use a large wood clamp to make it fit properly. It only took like 30 minutes though.
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