mpg, nightime driving vs daytime driving

no traffic maybe

and air gets thicker as it cools down.

 

I have heard that as well snowwy. Something about thicker air adding fuel mileage or thinner air adding fuel mileage don't remember. I think the no traffic has more to do with it though.

 

Could be that you had more down hills on the way back then you did on the way there. You have to take a much longer and more inclusive test to be accurate.
Cooler air does make for better combustion in a motor however.

 

I think at night you are naturally more cautious and naturally accelerate smoother and constant. And yes supposedly at least on a gas engine. the colder it is the denser the air and closer to complete combustion. The reason behind the cold air intakes on the rice burners with fart cannons. Well thinking about it it has to have the same effect on a diesel too because of the intercooler. Thats it purpose is to cool down the charge air.

 

Traffic and cooler air along with POSSIBLY a more uphill going and downhill coming back sound possible. I get better economy in my Ram 2500 when it's cooler for sure!

 

a long long time ago. i was actually thinking about a private pilots license. completed the ground school. got half way through the flying time. till that lesson came along where the instructor makes the plane climb sharp enough to the point of stall. and he slows the engine down enough that you can actually see the propellor spin.

needless to say. i don't have a license.

but one of the lessons was denser air in the winter time. planes can fly at a lower rate of speed. and propellor planes can fly higher.

don't know about the rest of the country but utah has a very high rate of accidents in july and august. you listen to the news and it's not hard to figure out they went into a stall.

 

One might also consider the regional market blend of the gas he was buying during the junket.....he didn't say BUT if he bought city gas during the day when it was hot....vs country gas ( out of attainment area ) purchased at night or at a lower temp then he would see a diff in the mpg's......

 

I'm seriously flabbergasted here. I hate to sound mean, but seriously, did any of you pay attention in school, or is the ability to think no longer taught? this stuff is basic physics. a car, truck, whatever will always, always always get better fuel efficiency at night compared to daytime. sorry if my harsh statement upset anyone, this stuff drives me postal and makes me rip my hair out

just in case someone really doesn't understand why night time driving is more fuel efficient I'll try to explain.
coolor air temperature means more oxygen per volume of air. it's just denser as it cools, samething with every other molecule on earth. oxygen is a combustible energy source so more oxygen molecules equates to more energy per combustion stroke each cylinder in your engine makes. so less fuel is needed to create the same amount of thrust to propel the vehicle down the road.
there is also the drag hot temperatures create, in this case friction. have you ever walked across a parking lot on a hot day? feels like you got glue on the bottom of your shoes right? same thing is happening to your tires. more drag means more fuel must be burnt to create the same amount of thrust.
also, hotter road surfaces create high tire temperatures, creating yet more friction.

 

In the day time it is hotter meaning your cooling fan will have to come on more often.
This draws power and thus burns fuel.
This is partially balanced out by the alternator working more to carry the extra electrical draw from the use of lights.
The draw from the fan however is more then that of the alternator.

As for the denser air at night this is true but on a turbocharged inter-cooled engine this is all but negligible.
On naturally aspirated engines it plays a real roll just like altitude does.