Body changes are modest with the 2012 Mercedes-Benz C-Class, but there are some big changes under the hood.

Beauty should be more than skin deep.  So, while most makers will be pointing to the all-new sheet metal they’ve got on display at the upcoming Detroit Auto Show, expect Mercedes-Benz to be pointing out what’s underneath when it comes time to preview the new 2012 C-Class.  And, curiously, the German maker will have the car on display only during a brief backgrounder for journalists, but not on the show floor at Cobo Center.

In fact, the cosmetic changes to the popular luxury sedan will be relatively modest, especially on the exterior, with a new aluminum hood and updated headlights and running lamps.

Sitting behind the wheel you’ll notice a bit more significant update, with a new leather-wrapped wheel lifted from the CLS and a completely redesigned dashboard, now aimed to spotlight the new high-resolution, multi-color instrument cluster.

But you may need to read the manual – or actually listen to the salesman’s spiel to discover all the additional features, notably including safety updates like Blind Spot Assist, Lane Keeping Assist, Adaptive Highbeam Assist, Attention Assist – which will flag you when you appear drowsy – and Parktronic.

The 2012 Mercedes-Benz C-Class gets a significant interior update, including an all-new IP.

Another place Mercedes offers some assistance is at the gas pump.  The maker claims to have improved fuel economy by up to 15% with the introduction of two new direct-injection engines and an updated 7-speed automatic gearbox.

The top-of-the-line powerplant for the C-Class will now be the C350’s 302-horepower V6.  That’s up 34 hp, while torque jumps from 258 to 273 lb-ft.  Using the BlueDirect process, the maker says, it has been able to bump up performance and mileage simultaneously, the C350’s 3.5-liter powertrain driving 0-60 times in the low 6 second range while fuel economy improves 5%.

The big mileage gains come from the new turbocharged 1.8-liter inline-four that will power the C250. Combined mileage is 24 mpg – 15% better than the old C300 — with 0-60 times rated by the maker at 7.1 seconds.