Last weekend I replaced my expansion tank due to the level sensor crumbling and ultimately breaking off completely. The next day after I replaced the tank I was about to throw away the old tank when I notice a rubber gasket on the main return line from the tank. My car does not have any leaks and I bought my replacement through Bavauto. Should I pull mine tank back out and check to see if there is a new gasket? see picture

 

It might not hurt to look, but then again if you don't have any leaks maybe it's ok. My guess would be that the new sensor has a new gasket already on it. If you bought the tank as a complete unit with the sensor already installed and it's not leaking, then I would just leave it alone. If you had to install the sensor to the new tank, then maybe you might want to double check. I know this infor doesn't really help you any, but I am sure if that seal is missing you would see a leak.

 

that is the coolant line to the engine not the sensor.

 

Ah, yeah I would think that the seal might not be there, better you check for it just to confirm.

 

the expansion tank on my 545 just shat the bed at 60k miles.....is it normal to replace these tanks at 60k intervals?

hopefully the new one i bought has been improved, mine failed at the boundary between the mounting boss and the thin wall part of the tank, looks like the mounting boss was insert molded due to material thickness differences and the material flow in that part of the mold did not bond well.

100deg C at 1 atm pressure does not seem like a reliable situation for plastic of any kind

 

Mine lasted until 76K miles on my 2004 545i, but it is a combination of age and heat cycles that causes many of the plastic components to fail. If you haven't addressed the rest of the coolant system components (water pump, thermostat, hoses, vent tube) now is the time. Cheaper to replace the parts at your leisure in your garage than to risk overheating (read gasket damage or worse) and require a tow.

The two halves of the tank are molded separately and either joined with an industrial adhesive and pressure or sonically welded. Either way the part is crap. I have owned 20+ different cars, driven to many more miles than my BMW and never had an expansion tank fail before the BMW. But of course none of them drove like "the beast" either.