Keep in mind I live in Florida so hills don't exist here.

So I went on my first real road trip and used cruise control 99% of the time, the trip was around 2.5 hrs there and 2.5 hours back on the highway. Before my trip my mpg was 37.2 and it's been steadily around there since I got my car in November.

I just got back from the trip and my mpg plummeted to 36.9. Why would this happen while using cruise control the majority of the time? I haven't seen my mpg below 37 before.

 

That's common. Cruise is not as good as a gentle right foot.

 

In the frozen tundra, we regularly see 10mpg drops in cold weather, so I must admit I had a little chuckle when I read where your mpg "plummeted" to 36.9 from 37.2.

Cold air is the biggest culprit with mpg drops. It's denser, takes longer for the engine to warm up, creates more drag on the vehicle, and burns more fuel.

What else cuts mpg? Strong headwinds, use of a/c, over or underinflated tires, etc.

I doubt using cruise had anything to do with an mpg drop. More likely other factors.

 

How did you determined the amount of gas used? The logical way is to top it off when you start, and top it off when you want to determine the amount used. Using the pump stop to determine the amount used will not be accurate because variables can cause the pump to stop too soon or too late. The honda average mpg indicator is always 2-2.5 mpg higher than accurate calculation.

 

 

I would not consider a drop of 0.3 mpg as 'plummeted'.

What speed did you set your cruise control at?

 

Are you kidding me? Plummeted?
0.3 fluctuation on a 5 hour round trip road trip is NOTHING.

Basically you went on a road trip and your mileage stayed about the same.

There are nearly countless factors that can impact MPG on that minimal of a level.

Reported EPA specs are up to 40 MPG highway, 33 city and a combined MPG of 36 MPG.

Usually on a highway drive my MPG does increase. But that fluctuation? I really wouldn't worry about it at all. I'd say on the few multiple hour, freeway trips I've taken, my mileage has increased on the trip, upwards of 38-40 mpg.

You're overall getting about exactly what is reported as what The Fit should get in combined driving.
If you have a problem?
I hate to say it but things will get worse, and be more noticeable.

At this point? Maybe a little strange that you went on a highway drive and the MPG didn't increase, but I'd file it under absolutely nothing to worry about.

Usually I refill the tank, and reset the trip computer right before I go on a road trip, making it easy to see exactly what MPG the vehicle is reporting for that trip alone.

 

Many years ago, driving a VW Squareback (yes, that long ago) I noticed a 5 mpg differential going east/west on a 650 mile trip. It was the headwind!

 

Ok yes it didn't plummet but it did go down when I expected if anything for it to go up. Everything I read online about cruise control said it's more efficient. I just found it weird for it to go down that low when it hasn't gotten bellow 37 since I got it.

I'm also wondering how other people here report getting much better mpg than me. I live where there's no hills, no cold weather, mostly highway driving and still around 37 mph while other people can get over 40.

 

Look up hypermiling techniques for some tips. I can regularly get 40+ MPG by utilizing some smart driving techniques.

 

Do you use the AC? If yes, that is why.

 

Yes but I always use AC so this is nothing different. It was on the lowest setting the whole time.

 

I average better economy in town vs highway simply due to that fact that I drive fast on the highway.

I have noticed the best highway mpg when I drive between 55 and 65 mph. If I average closer to or exceed 70 (as I usually do) then mileage drops precipitously. A highway trip staying under 65 and averaging 60 will net me 43-45 mpg. If I average 70+ I'll get mid 30s or less.

And I always get better mileage using my foot. Cruise control makes poor throttle choices because it tries to maintain set speed no matter what.

This is all according to the computer which should be taken with a grain of salt. I also rarely use AC.

 

Generally, unless you drive like a jackhole, cruise will always be worse. If one has a clue how to use the throttle, you'll always beat it.

 

You asked why you seem to get worse MPG than many others.

AC is at least a partial cause.

 

Yup. I get significantly worse mileage when the AC is on.

 

I doubt that cruise / no cruise is as big a factor as the speed and wind. How fast were you going? Even if it wasn't windy, if you're on the interstate with a lot of other cars around you the air coming off the other cars also has an effect. Also, was the Econ button on or off? Was it the same in both cases?

 

With cruise control during morning work commute, I get between 38 and 41 MPG at 65 mph.
In the afternoon work commute, I don't use cruise control due to traffics, I get between 33 and 37.

So, with cruise control on or off, the slopes, headwinds, etc..... will cause the mpg to be out of wrack.

 

I just took my first road trip in my Fit and noticed one major factor in mpg at highway speeds...

SPEED.
In areas where I was doing about 70 mph, I was getting about 36 mpg.
about 60 mph = about 40 mpg
and about 50 mph = about 42 mpg

These cars are streamlined, but they are tall and the flat vertical hatchback creates a monster vortex. So getting up to and maintaining higher speeds takes exponentially more fuel. (Add to that the kind of sadly high geared 6th in the MT)

Being in Florida on a road trip, I can only imagine you would probably be going 70+ mph, so I would imagine that is where you saw the unexpected mpg figures(at least the largest influencing factor)

 

how fast were you going? if over 65mph it can get worse mpg. i was easily getting 42mpg+ while on my commute at max 60mph..