Picked up my 2018 IS350 F-sport AWD about a week ago and figured I'd throw some fuel economy numbers out there. Obviously, you don't buy a car like this because you're concerned about fuel economy necessarily, but it never hurts to get good gas mileage.

I'm actually pretty impressed so far. This car seems to be pretty bipolar when it comes to fuel consumption, but it also seems to be manageable.

With adaptive cruise and Eco mode on highway commutes (50 miles rd trip, light traffic) I'm easily averaging 31 mpg at around 75 mph. In heavier traffic, the average seems to drop down to 29 or so. With adaptive cruise off, I can drive identically and the fuel economy worsens to around 27. Letting the car do its thing seems to really allow it to achieve the best highway MPG.

City driving is where the bottom falls out as I'm getting around 17. If I chill out on the throttle, achieving over 20 in stop and go city driving is seems pretty easy.

Driving aggressively obviously kills economy in this thing. I've had a few "sporty" cars and this one definitely does the worst MPG-wise when driving hard (seemingly worse than my 2013 SRT Challenger) Otherwise, love the car. I had high expectations and it continues to exceed them, even in the power department. The little 5 hp boost in 2018 seems to give it a noticeable extra kick. Great ride overall.

 

You're breaking in the engine, drive it hard at various RPM's! Don't mess around with Eco mode during breakin

 

I've mostly been doing that. Been driving it in a lot of different scenarios to see what happens.

Interesting about Eco mode...why is that?

 

You want to vary the RPM's during the break in period. Eco mode will shift to the highest gear possible at given speed in a bid to save fuel. Your RPM's won't move much in Eco mode.

 

I read not to use cruise control as well. But also don't go over 4k rpm. I think I get mixed of 25MPG or so with 75% highway and 25% city drive.

 

 

I didn't read the manual on my IS yet but a lot of times manual does indicate that you need break-in while others tell you that they are already broken in from the factory.

 

If you drive other brands, they sometimes come broken in from the factory too

 

I definitely went above 4000 RPM on my third day with the car, only 200 miles on the clock at the time. I wouldn't recommend putting the pedal all the way to the floor though, or driving hard for more than a few minutes, since the whole point is to vary the RPM. I don't think there's anything really to be concerned about as long as you're not being a d*** to your car.

Congrats on the car, and I must say those MPG numbers are not bad at all, but then I have the AWD version which is far worse in that regard. Even so, I notice the difference in city and highway is pretty huge - I got about 28 MPG on a 70-ish MPH highway trip recently, but then it's back to 19 now that I am just commuting again (which is mostly city).

 

I have the AWD too. And yeah...I drove the **** out of it the day after I got it. We're blessed with some really empty country roads here in the Nashville suburbs. It's definitely been able to run the gamut as far as driving situations.