In any event, the AdBlue constitutes just one more gauge for owners to eye warily.

WSJ: 2013 Porsche Cayenne Diesel Review: Only Geeks Need Apply | Rumble Seat by Dan Neil

Another compromise has to do with the full-size spare tire, which goes missing in the Cayenne Diesel, displaced by the AdBlue reservoir (diesel models get a space-saver spare).

WSJ: 2013 Porsche Cayenne Diesel Review: Only Geeks Need Apply | Rumble Seat by Dan Neil

Also, to comply with prevailing U.S. emissions standards on nitrogen oxides, or NOx, these big diesels require fairly complicated systems of postcombustion treatment with a water-based urea solution, called AdBlue.

WSJ: 2013 Porsche Cayenne Diesel Review: Only Geeks Need Apply | Rumble Seat by Dan Neil