2017 Passat SE 1.8L Troublesome MPG / tank
 

I just turned in my 2014 Passat SE 5-cyl and leased a 2017 Passat SE 4-cyl. My 2014 use to give me about 330-340 miles to a tank of gas, mainly city driving. I've filled up twice in this 2017 with more highway than I've ever driven and I'm not getting any more than 270 on a tank. I'm frustrated because I opted for the 4-cyl due to the reported better gas mileage. I do sit in my car idling a lot (with both vehicles), and my mpg monitor tells me on this 2017 that I am getting FOUR mpg while idling. Does anyone have a similar issue or should I take it in?

Thank you!

Welcome to the forum. Your experience just goes to show how optimistic instantaneous fuel monitors are. When you are sitting stationary and idling you are getting ZERO miles per gallon.
In theory you could sit there and burn an entire gallon of gas without going anywhere.
Anyone who idles when there is no need to is wastefully burning fuel. I even switch off at long red lights.
Highway driving can be pretty fuel guzzling if you drive at high speeds. It takes FOUR times as much fuel to travel at 80 mph than at 40 mph (all else being equal).
Other issues that could be affecting your MILES PER TANK is your relative inexperience of the vehicle (compared to the one you were used to), and possibly even a marginally smaller tank.
Have you tried filling up full, driving until you need to fill back up, again fill up full, and divide the miles between fill ups by the number of gallons you had to put in? That is the only true measure of fuel efficiency. And even that is best done over several tankfuls.

In addition to learning a new car, there is a break in period for components before best efficiency is reach. This is mainly the tires; they have higher rolling resistance when new.

The 4 cylinder engine has a turbo. Small displacement turbos can return good fuel economy, if you can stay out of boost. Drive them for the power, and they can suck down the gas.

I am having a similar issue with Toyota Corolla. I drove a 2003 model for almost a decade - always got between 280 - 340 miles per tank - depending on % city vs highway driving I was doing (and in L.A. city driving is terrible for FE). Bought a 2015 Corolla 2 months ago with only 35k miles on it, and now I'm barely getting 250 miles per tank - when I fill up putting in about 11 gallons, so do the math and I'm getting LESS than 23 MPG in relatively new car! Corollas are advertised at 28 city/ 38 highway.

I've taken it to 2 mechanics and the Toyota Dealership, had the oil changed (synthetic) and everyone says everything under the hood looks totally normal. The tire pressure is fine. I try to be light on the gas pedal and never unnecessarily accelerate. I coast into lights, put in neutral downhill. I have run the AC a lot as it's been hot, but I did that in my old car too.

I've seen people on the forums recommend turning off the engine at long red lights... Is that good to turn the car on and off so many times? It would probably save me a good amount of gas because I spend 2 days a week sitting in 90 mins of L.A. rush hour traffic (pacific palisades to hollywood at 530 pm = total nightmare).

Any thoughts anyone? Any ideas much appreciated.

-Johnny

That's right. This is the reason I always tell my teen agers not to wait inside the car with air condition turned on. They are wasting fuel.
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