SLOW leak at bottom of Coolant Expansion tank :(

[MO525]

1993 525i M50

I read a post some time ago about replacing an o-ring at the bottom of this tank?
I have to remove the coolant level sending unit as well?

To do this service, I'm assuming all I'll need (part-wise) will be an o-ring for the tank and a gasket/o-ring for the sender?
I prefer to have all my "ducks in a row" for less downtime for the car.

Thanks for your help and feel free to e-mail me directly.
Bill

[AZ_Jason_S]

I would suggest getting one of the clips that hold the radiator to the core support. I broke mine removing it. Possibly also 1 or 2 of the expansion nut that hold the shroud to the radiator. You have to remove the black plastic cap on top of the tank. The clip for the radiator/support inserts into that. I think the shroud also inserts into that piece. After you get the 3 allen heads off, pop the black cap piece. Then the tank just lifts out. It may not want to at first but just keep working on it. There is one O ring around the bottom, another small one on the top. I only really needed the bottom one, but I did the other one anyway. Took me about 20 minutes. Also, I tried to clean the mating surface down in the rad. where the tank inserts. I also put a real light touch of grease on the big O ring. I didn't want it to tear when I pushed the tank back in. Lastly, I didn't do anything with the sending unit.

[MO525]

I would suggest getting one of the clips that hold the radiator to the core support. I broke mine removing it. Possibly also 1 or 2 of the expansion nut that hold the shroud to the radiator. You have to remove the black plastic cap on top of the tank. The clip for the radiator/support inserts into that. I think the shroud also inserts into that piece. After you get the 3 allen heads off, pop the black cap piece. Then the tank just lifts out. It may not want to at first but just keep working on it. There is one O ring around the bottom, another small one on the top. I only really needed the bottom one, but I did the other one anyway. Took me about 20 minutes. Also, I tried to clean the mating surface down in the rad. where the tank inserts. I also put a real light touch of grease on the big O ring. I didn't want it to tear when I pushed the tank back in. Lastly, I didn't do anything with the sending unit.

Fantastic.
Glad to hear it's an "easy" job.
I need to get rid of that leak, it's irritating as can be!

Thanks for the step-by-step explanation.
I'll get the o-rings ordered asap.

Bill