I have an old 06 Malibu Maxx with the 3.5 , a good beater car but I'm getting old and I have to nod forward to see the speed, so I bought one of those OBD headsup displays and it is easy to read. One of the things it has is an instant liters per hour readout. Yesterday it was+5 degrees and at an idle the reading was 1.4 L/Hr. Today it is -20 and the reading at idle (after a half hour drive) was 1.8, so is that because the volume of the gas is less or is it a cold temperature adjustment by the ECU. It looks like a kinda useful information display because it give you an indication of how the engine is at idle