Better mileage going faster
 

Most of my driving has been short trips - to and from work. The past couple of days, I've had to drive about 50-60 miles on Interstate, other highway, and city streets. I've found that I got more miles on this tank than the 3 previous tanks. Being that I work nights, I end up in some pretty crappy traffic, and couldn't really help but to go with the flow of traffic. So, can anyone tell me why I get better mileage driving faster than slower?

All else being equal, short trips are going to get much worse mileage than the long ones. Plus, you could be benefitting from the "corridor effect" at speed on the highway in heavier traffic, where the sheer volume of traffic has set up a flow of air that makes a difference.

Are you doing any stop & go on your short trips? How short is "short": does the car have time to get warmed up? How much of the time is spent in a lower gear? All these might be contributing to lower FE.

You are also going faster than you are when doing city driving at a stop-go rate. My vehicle can do 1500 rpm at both 25 and 55 mph, but i'm covering more ground per revolution at 55. Of course there are issues of drag, but if you look at most EPA estimates for cars fuel economy, universally the highway mileage is higher. I'm pretty certain that outside the fact you are able to travel constant rather than regular accel/decel, it is that you are in a higher gear at an RPM rate close to what you would have in a lower gear in slower speeds.

On the interstate, I was hitting upwards of 80 mph at about 3500 rpms. I don't draft because it scares that s%^& out of me. I can see the corridor effect doing some, but that much??? I still haven't refueled. Currently the car is in the air awaiting a rebuilt transmission. I'll post in the fuel log after I refill.

As for my short drives, its about a 10-15 minute drive of about 6 or 7 miles. With the heat down here, the car warms up fast. I keep the rpms below 2500 all times, and coast frequently (engine on). There is one light that is always red when I hit it, but its a quick one and not worth shutting my engine off. I'm quite careful of the throttle position and dumping unneeded gas into the engine.

As I try to answer my own question, I keep thinking "buy a scangauge" (I also read it a lot) but I can't afford the cost on top of everything else right now. I suppose that would lend to better understanding of whats going on under different circumstances.

I just installed a vacuum gauge about a week ago, and while driving at 55 you can see a noticeable effect of drafting, from as far away as 150ft. My vacuum gauge would show higher vacuum as soon as I came into the draft, sometimes as much as 8 in.hg. The more cars ahead of me the farther back I could be as well. So you don't necessarily have to be close to draft.

bbjsw10 -

Oooooh, that sounds like MPG radar!

CarloSW2

Exactly,:thumbup: :D

Yes all of that, and he may be stopping/starting more off of the freeway.
Steady 70 mph is better that top and go any day...

better faster
 

Yeah,the stop & go kills your momentum and will eat your lunch.And any trip less than 22 miles means the car never completely warms up,so it's road load is higher than in the longer commute.I loose half my mpg in town,where it could be the other way around.Welcome to traffic!Hybrids help a little here,as they recover some of the otherwise"lost" energy,but as long as congestion persists,we'll be forced to pay the extra tribute at the gas pump.