Radi

I have tested fuel economy on my CTT 2014. And I am surprised that it can run 24mpg with 4 people on board and luggage I keep speed between 50-70ml. My friend has a CTT 2018 with 4.0 V8, and has exactly the same fuel efficiency. Strange, initially I thought that I can’t even be closer to fuel efficiency to new V8 4.0 I now it shuts down a cylinders at low speed.

will_atl

Once the car gets rolling, the effort to keep it rolling is less, and neither engine works crazy hard.
I daily drive an S450 (a V6), and on the Mercedes forum I posted my mileage, and the guys with S560s (V8) get pretty similar mileage.

Gus B.

Here is another reference point... 2013 GTS (4.8, not TT), similar distance, similar fuel consumption, but I was obviously stuck in a lot of traffic:

NKCowboy

I am the new owner of a 2015 CTTS. First measured fuel economy, comparing gas receipts and odometer: 14.4 l per 100 km = 16.2 mpg. Disappointing. Especially because the measured tank was almost all highway cruising. Porsche's claimed highway mileage and the reports above indicate I should be getting some 40% more fuel economy.

TPM normal. Cool weather.

I did have a roofbox on top. Could that produce so much drag?

mk85911

I recently moved on from a 2014 Cayenne S with the NA V8 to a 2024 Cayenne S with the twin turbo V8, and the gas mileage from the trip computer showed virtually identical results over identical driving routes. Based on published data, the new Cayenne S is about 200 lbs heavier. Mike

Go2GuyTX

I wouldn't think it makes a HUGE difference, but it definitely will make A difference.

Just bought a 2017 CTT and I get about 19.4-19.8mpg avg (mostly) highway, but my average speed shows 73 in TX... When I got it 2 weeks ago it was about 18.5; ran a bottle of Techron through it and then a fuel injector cleaner on the following fill up as well, jumped it up to 20.5ish mpg (computer). YMMV but its a cheap option to try!

TNelson

FWIW, we noticed <10% mileage drop on my daughter's Outback when we put the roof box on (23 vs 25MPG)

NKCowboy

Average speed on the French Highways for me is the speed limit which is 130 km/h = 80.8 mph. So that's one reason my mileage was worse LOL.

I will try an injector cleaner. Thanks for the suggestion.

NKCowboy

A bit less than 10% drop? Well, maybe more in my case since I was cruising at 80 mph.

Go2GuyTX

Debatable... lol, Posted speed limit of 75 is typically running 80-85mph here. Which is why I thought it was running a little lower (and why I specifically said avg speed of 73, haha)... but then the Techron bumped that up running the same route at the same speed. Let us know if you end up seeing any improvements, I would be curious if its beneficial overall :-)

Go2GuyTX

I want to know how to get 24mpg running closer to 70mph+ :-D I'm currently debating when to add an FVD tune as talking with @Rhonda@FVD she said they typically see 2-3mpg improvement, which I would gladly take... the more mpg I can squeeze out, the better. Even at 20mpg, Im not unhappy

Tappet

It's interesting how much difference altitude makes too. I bought my 2017 CTT in Denver, which is pretty high up, and driving home through the desert, the range remaining would say 560 miles on a full tank. I was getting around 25mpg and I wasn't gentle with the gas pedal. Here at sea level, the best I can do on pure highway drives with no traffic is about 22mpg. Driving up into the mountains, I get 18 mpg up, 29 mpg down. Driving a lot around town, my average is 12 mpg.

Gus B.

At sea level, high average temps (mid 80sF and up/30ºC and up), 70% stop & go traffic/ short distances, the other 30% in "highway with a lot of traffic" (average speed of 75km/h = ±45mph), I have averaged 12.71 mpg (18.51 L/100km) over the past 1,900 miles (3,000 kms) on my 2013 GTS. Tires are Michelin Latitude Sport 3 in the stock 295/35/21 size.

My consumption figures are based exclusively on actual distance driven (as measured by the trip odometer in the dash) and the amount of fuel put in at the pump. My onboard trip computer shows a fuel consumption figure that is "significantly" less than my measured result. My figures have already been mentioned, but as per the PCM summary page (mileage equates to what I have in my spreadsheet) the consumption is 15.05 mpg (15.63 L/100km).

Go2GuyTX

Very valid point about sea level (same as me)... I'm curious, what size tires are you running? I know stock is 275/45R20 but mine came with 295/40R20... this makes the speedometer even slower than from the factory, so I don't even think I'm traveling the miles it claims I'm getting. When it's time for new tires, I'm going to 275/50, 285/50, or 295/45; haven't made a final decision yet.

RhinoComp

Roof box can make a huge difference. I've found our Thule box mostly just increases the negative effects of any wind on the drive with respect to fuel economy. During a road trip to Montana last year, I averaged a hair over 20mpg on the highway in my V6TT S. However when we drove to Texas more recently, trip average was closer to 17mpg. The windiest day of that trip I think netted around 15mpg for the day.

For comparison, I typically get 22-23mpg on my standard daily highway commute, without a roof box of course.