Folks,

Seen a few inquiries as to how to replace the fuel filter, and especially the O-rings on our X350's. Hope this ditty helps to resolve some.

Note that the fuel filter in 2004 and later vehicles moved to the same location as BMW's: Under the driver seat and no longer within the driver side rear wheel well. You do not need to remove the rear wheel. This is because the fuel tank was moved from behind the rear seat to under the rear seat (again, like a Bimmer).

It's recommended that you disconnect the (-) battery terminal first. Blow down the fuel pressure, to minimize fuel spray while under the vehicle:
- Remove the blue Schrader valve cap on the driver side fuel rail;
- Place a doubled shop rag over the valve;
- Press down the valve stem with a Torx bit or otherwise, until the fuel pressure is relieved;
- Replace the blue cap (most important step:-).

You will expose the filter by removing an aerodynamics cover that runs the full length between each wheel well. Therefore, jack the rear of the car, then place it down on floor stands beneath the rear frame (on-frame mount of the control arm, etc.). Remove the jack, as it'll be in your way. Use a 10 mm, 1/4" drive socket to remove the cover fasteners (combo of nuts & screws); the recessed ones will need a 2" extension. Remove the fuel filter's steel protective plate / bracket (10 mm). Be sure to use anti-seize on all fasteners when replacing them.

The fuel filter remains the same (I believe it requires a 16 mm and a 20 mm wrench). Note that the forward fuel tube slides forward for filter extraction and replacement. We may get lucky reusing the oil drain plug washers, but O-rings take a more significant set and should be replaced. The $3 Jag O-rings are 8mm x 1mm; try to find red TFE ones if you can, but black Nitrile is OK.

The copper fuel tube ends are flared and have sharp edges, so do not install the O-rings over these edges directly or you can imperceptibly score them. Instead, load both O-rings on the end of a Ø3/8" smooth dowel, and slide each one onto a fuel pipe.

Inspect the copper fuel or brake tubes for any corrosion. A bluish green sediment is trouble, but a green or black color is normal oxidation. If sediment (metal salts) is present, look for areas where the lines contacted the aluminum car body. This can be real trouble and should be addressed.

For the clever ones: Never use Teflon tape on the fuel filter nuts - that's what the O-rings are for - as the tape may enter the fuel system an wreak havoc. Over tightening the filter nuts is not necessary.

Again, hope this helps.
Rob