...cabbies put sheets of cardboard behind the front grille of their Hackney Cabs ?

Seen it done for years and always wondered, then saw another at lunchtime.

I believe that it's to stop the engines getting too cold. Diesel goes lumpy when it gets really cold and can clog up the injectors.

+ it looks Cool

And of course in the winter, the heater may not work the best, so blocking up the rad can help keep ur toes warm