In addition to the styling tweaks, power could grow considerably.

Mercedes-Benz engineers are hard at work developing the refreshed E63 saloon and estate at the Nurburgring before snowy weather stops development at the Green Hell for the year. Check out the video above and the one below for a look at the camouflaged machines.

Both vehicles wear camouflaged wraps over the front and rear. The nose has a revised fascia that appears more angular than the swoopy piece on the current model. The large inlets should let plenty of air into the engine bay. These cars don't yet have the Panamericana grille with vertical slats, but this element should be on the production model. New headlights have sharper edges than the lamps on the existing vehicle.

At the back, the changes are harder to see. New taillights appear to be among the tweaks. The four, trapezoidal exhaust tips are still an eye-catching part of the rear.

There aren't photos of the interior yet, but the E-Class allegedly gets an updated infotainment system that should better match the look of the latest Mercedes models. 

Gallery: Mercedes-AMG E63 saloon, estate facelift spy video

The revised E63 should retain Mercedes-AMG's twin-turbo 4.0-litre V8. It makes 603 bhp currently, but there's room to boost the output because the mill produces 630 bhp for the GT 63 S Four-Door Coupe. For comparison, the Audi RS6 Avant is the E63 wagon's primary competitor in the performance wagon segment, and the latest version from the Four Rings packs 591 bhp from a hybrid-assisted twin-turbo 4.0-litre V8.

The refreshed E63, plus the rest of the E-Class lineup, should debut in 2020 and be on sale at least in some markets before the end of that year.