I bought the car (my first diesel) in May, so no experience with the cold. The auto has drag at the torque converter that presents a load to the motor, so it warms up quicker than the manual. The coolant glow plugs not only add some heat to the coolant, but they also present a load to the alternator. That's why they are there, or so I understand. One user said working coolant gp's make the car warm up 30% quicker than without.