Will an E93 rad cap fit E53's? NOPE
 

E53 V8 and I6 rad caps are the same.

Will the E93 1.4 bar cap fit? 17 11 7 521071

I saw a thread where SlckGT1 put it one on. Would like to confirm please.

EDIT: No, it wont fit correctly. It will screw on but the inner sealing surfaces are different .

I don't know about that but the E30 one does if you're looking for a lower pressure cap

Thanks Josh, I did see that in the same thread.

I was planning to get an E30 one but I may be able to get an E93 one for free.

That would be $15 saved for the maintenance fund if it fits.

www.realoem.com

Find the object of your desire for your car and click the part number. Follow the link to a list of all other cars that use the same part. If the E93 (current model of 3 Series) is listed then the answer to your question is yes, else it is no. If no, then there can be differences that you need to explore further to see if the part will physically fit or not.

If you can get it for free just get it and try it out and if it fits let us know

Jd, checked realoem already and it crosslinks to mistly newer F-series vehicles.

RB, I was gonna order that E30 1.2bar cap but this came up. In the thread you mentioned the E30 caps, Slick mentioned he used an E93 cap.

The 11 digit BMW part number you gave (17 11 7 521 071) at realoem.com or bmwfans.info...the e93 is listed but the e53 X5 is not: RealOEM.com - Part Search

It won't cross link to E53 because the system is "spec'd" to 2.0 bar - the E30 cap I linked and the F series cap SlickGT1 linked will work - I prefer the E30 cap since it looks the same as stock.

Q, yup did the search and its all newer cars, thanks for linking that though.

RB, thanks!

You're right, the E30 cap looks exactly like stock but for free, I can get used to the different look.

Will report back here when I get it and put it on.

The 2 caps are similar enough but differ in some areas that one might not work properly in the other system.

Here is the E93 cap:
http://i239.photobucket.com/albums/f...psygyrrzbd.jpg

http://i239.photobucket.com/albums/f...psowkisf4j.jpg

http://i239.photobucket.com/albums/f...psfnkjn37o.jpg

E53 cap beside E93 cap:
http://i239.photobucket.com/albums/f...ps7jrwccwq.jpg

Note same number on relief valve even with differing pressure rating:
http://i239.photobucket.com/albums/f...ps8hqndjwf.jpg

Differences:
First, a pic of the expansion tank mouth. This is an old tank of mine that I replaced because it had a slight leak at a seam. The white stuff is wax, to see points of contact between cap and tank.
http://i239.photobucket.com/albums/f...psqkjtwbmb.jpg

Stock cap has a rubber seal that engages the step in the tank mouth.
http://i239.photobucket.com/albums/f...ps8xbx0ftg.jpg

E93 cap doesnt have this seal, it has an O-ring that engages the inner wall of the tank mouth. However, the measurements are different enough that the O-ring doesnt engage the tank mouth. Wax didnt smear in that area when I tried the E93 cap.
http://i239.photobucket.com/albums/f...psckkajkbk.jpg

Also, if you will look at the tank mouth pic again you will see 2 bands where the cap valve O-rings engage the tank body when the cap is screwed in. Problem is the E93 cap valve sits higher and screws in less than the E53 cap, so the valve will not be in the same position.

http://i239.photobucket.com/albums/f...pscaldihsq.jpg

TL,DR: Cap threads are the same and cap valve is same diameter but E93 valve lacks upper seal and sits in a different place in the tank compared to an E53 cap.

That is one big ass ugly cap, E30 cap ftw!

If you want another option check german auto solutions I have the billet caps on both my 540 and e53 they work and look great

The GMS caps are nice! For this particular part under the hood I personally am not wanting to spend more than necessary though.

RB, it actually looked decent when it was on. Filled up the space and was flush in the area, did not stick out like a sore thumb like i had imagined. I wouldnt have minded using it at all if the valve fitted properly.