Older Mercedes-Benz petrol engines with the 'K' symbol are supercharged, not turbocharged. Superchargers are not run by impellers in the exhaust system so do not get so hot. However, since 2009, Mercedes 4-cylinder petrol engines have been turbocharged rather than supercharged. These turbochargers are water cooled with a pump that feeds coolant through them after the engine has been switched off. But it’s still wise to idle them for 30 seconds or so after a long ascent, after towing or after steady speed on the motorway.