Expansion Tank Location Options

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bhamilt8

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Joined
Sep 26, 2025
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Hi all,

I'm new to this forum and optimistic that I'm in the right place to get some help! I've got a '98 z3 that used to be a 2.8L car. Long story short, I bought it with a blown engine thinking it would be a good recipient for an N52B30 with 6spd transmission I had. The engine and trans is in the car now, but it sits a little closer to the radiator and the expansion tank no longer fits in the factory location between the rad and cylinder head.

I would like to get some recommendations for where it can be located. From what I can tell, M54 cars had the expansion tank behind the drivers side strut tower. I obviously won't be using the ??cruise control?? module that used to sit there, but I plan to keep the ABS pump. Does anyone know if the M54 expansion tank will fit? Also, I believe the M54 expansion tank has 2 outlets. Do you know if the S54 version has a single outlet?

Finally, I'm happy to hear other recommendations for expansion tanks. I plan to do a write up of the work I did to get the N52 into the car, but I'll wait till I'm a little further along the process. I need to get the EWS deleted on the DME, so I still haven't started it in the car.

Thanks for your help!
 
Hi and welcome from me, my ///M is the S50 variant that has one main outlet but has a return that runs down the passenger side to the radiator. The tank sit next to the bulkhead on ghe passenger side. If you look at my build thread link underneath my sig and go to the last page and scroll down you can see a pic of my engine bay giving you an idea what I’m on about.

looking at Realoem you can enter any BMW model to find part numbers of parts and google those to find pics of what your after if the diagrams don’t give you enough detail.

Look forward towards your build thread.
 
Thanks Althulas! I spend a lot of time on RealOEM - certainly would be much harder to work on these cars without it.

It looks like the S50 cars have the expansion tank where my DME is. Is your DME still on the far passenger side near the firewall (Bulkhead?)? I ended up purchasing an M54 expansion tank that sits right behind the drivers side strut tower (green outline in my picture). It will arrive in a couple of days, so I'll have to wait to see how it fits.

It looks like the m54 cars also don't have those three harness connectors between the fuse box and master cylinder reservoir. I can't find any information on the one I have circled in red. My wiring diagrams show a picture of it, but no reference to it throughout. Is this the X6031? Does anyone have a pinout for it?

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Just a quick update. right after I asked the question about the mystery connector, I ended up finding the correct wiring diagram for my car. Up to now, I've been using the AG Version for 1998 Z3, but I just came across a pdf of the US version encompassing my build date.
 
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