starting a vw sharan in cold frosty mornings?

my1998 sharan will not start in a cold frosty morning,if she eyentualy starts and the battery stays up,there is a lot of smoke for amout 2 mins.fitted new glow plugs but dont work in engine.bench test-working fine.heater light comes on dash for about 1 sec.CAN SOMEONE PLEASE HELP..