Originally Posted By: jldcol
Several factors here. Winter blend gas in more volitile, easier to vaporize, to help aid cold starting. Results in a "lighter" mix of gasoline, probably less btu's per gallon. Car is in open loop until o2 sensor gets to 600deg F. Coolant sensor also has to get to a set temp,(varies by manufacturer) for a set time before closed loop operation starts. You probably get ~1/2 of your warmed up closed loop mpg's with open loop operation. In summer temps can take about 5 min to get there. In winter 15-20 min or more if really cold (below zero).Cold air is denser and thus more air drag. Cold tires have much more rolling resistance than warmer ones. Lubes being cold less effect on mpg's, but still some as well.
I would think colder, harder tires have less rolling resistance than softer tires.
Time in open loop isn't much longer in the winter than the summer. For one, everything made today has a heated 02 sensor. Cars like my TL light off the convertors and 02 sensors and are in closed loop within 10 seconds of startup regardless of engine temp. Sure, it may run just a little richer until the coolant has reached a certain temp but it's not as drastic as older cars.
Don't forget there is *usually* more timing with cold intake air temps and colder coolant temps which can help mpg or lessen the hit from winter gas.
Cold denser air causing more drag as a reason for worse mpg is a stretch. Maybe in theory but I doubt it would be measurable.
Winter gas and longer idling is primarily responsible for the drop in mpg.
Several factors here. Winter blend gas in more volitile, easier to vaporize, to help aid cold starting. Results in a "lighter" mix of gasoline, probably less btu's per gallon. Car is in open loop until o2 sensor gets to 600deg F. Coolant sensor also has to get to a set temp,(varies by manufacturer) for a set time before closed loop operation starts. You probably get ~1/2 of your warmed up closed loop mpg's with open loop operation. In summer temps can take about 5 min to get there. In winter 15-20 min or more if really cold (below zero).Cold air is denser and thus more air drag. Cold tires have much more rolling resistance than warmer ones. Lubes being cold less effect on mpg's, but still some as well.
I would think colder, harder tires have less rolling resistance than softer tires.
Time in open loop isn't much longer in the winter than the summer. For one, everything made today has a heated 02 sensor. Cars like my TL light off the convertors and 02 sensors and are in closed loop within 10 seconds of startup regardless of engine temp. Sure, it may run just a little richer until the coolant has reached a certain temp but it's not as drastic as older cars.
Don't forget there is *usually* more timing with cold intake air temps and colder coolant temps which can help mpg or lessen the hit from winter gas.
Cold denser air causing more drag as a reason for worse mpg is a stretch. Maybe in theory but I doubt it would be measurable.
Winter gas and longer idling is primarily responsible for the drop in mpg.
