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We’ve had 2 TDI Q7s. Current one just hit 100000 mi on 1500 mile round trip to Fort Worth and back to Alabama. Over the years I’ve noticed that fuel mileage is very speed sensitive. Traffic runs pretty hard on I20 and I typically do too. Cruise set between 75-80 mph. ( limit is 75 in TX). This trip out the avg fuel mileage displayed was 26.4 over the 685 mi. Kind of disappointed with that so today heading home I experimented with setting the cruise at 70 mph. Over two separate samples of 10 miles each the avg fuel mileage displayed was 34.0 mpg!
Going 14% slower ( vs cruise set to 80 mph) yielded 30% more mpg! BUT you sure have to watch your mirrors at 70 mph. EVERYTHING passes you😏. This difference may be inflated a bit by the fact that we had the additional aerodynamic drag of two bicycles on a hitch mounted rack. Still— Over our 685 mi run to visit grandsons , slowing to 70 mph would save $25 in diesel cost each way. BUT it would add about one hour each way to our trip.
Last edited by J. Patterson; Apr 23, 2022 at 11:39 AM.
slowing to 70 mph would save $25 in diesel cost each way. BUT it would add about one hour each way to our trip.
Yeah I found similar results however despite today's fuel costs I make far more than $25/hr, and at my "**** off, I'm on vacation rate" it would even be in excess of 10x that.. Hypermiling these ain't my thing..
Yeah...I noticed the same thing here...significant mileage difference between 70 and 75 MPH. The other thing that really destroyed the mileage was the Yakima SkyBox. That thing would take the mileage down to 23 MPG and less. Fortunately, I was able to sell the SkyBox and transition to the EXO system.
I've found using the cruise control and tweaking speed to see where the 'sweet spot' is located works best for me on long trips, as it will vary depending on how the vehicle is loaded...the '10 on steel susp is more sensitive, and the '15 with air susp really doesn't care, as it self-levels and automatically drops at (my) highway speeds to optimize airflow/mpg. I've experimented with how fast I can go, semi-legally, and still maintain roughly the same mpg as driving 5-10mph slower, which has shocked me. My working theory is I've increased the speed of the engine to it's optimum output/efficiency, especially in our '10, which offsets the increased drag. Of course, the air suspension dropping down on the '15 once I've reached the threshold speed really helps, lol. What's nice about that feature is once engaged, it doesn't disengage until you go below a lower, preset threshold, so there's a fairly broad working range w/o losing the benefit.
Rather than hypermiling, my focus is how fast can I go and still get 'acceptable'/normal fuel consumption stats. It's all about that cruise control and proper spacing so I can adjust to traffic w/o hitting the brakes...and I don't drive slow.
Last edited by '10Q7TDI_Prestige'; Apr 24, 2022 at 04:47 PM.
Odly enough when I bought my 2014 with 75k miles I would hit 31mpg almost consistently with high speeds like 75-80mph trips of 300mi. Then as the miles went up to around 100k those numbers dropped down to about 25mpg. So I pulled the intake tube and sure enough, it was caked with soot. Soaked it in oven cleaner a few times, rinsed it, and reinstalled and sure enough my MPGs went back up. Did not have a chance to measure exactly but she sure feels like the old days.
Agreed on the intake runners; Audi actually cleaned those on our '10 (a real shocker!) when they replaced the EGR Cooler, and the tech remarked that it was plugged up tight with soot (108k miles), and so he cleaned it out. It was still running well, but once all the bad parts (leaky turbo too) got replaced, well, that car just flies now and is getting 26-27mpg over the road consistently, at high speed. I've also done the run on I-20 between DFW and Shreveport multiple times, and I get better mpg going out than coming back to DFW because of the elevation changes...it's uphill coming back, and then there's the wind in your face too.
On the topic of intake cleaning, what are the opinions of the Liqui Moly Diesel Intake System Cleaner? Helps...doesn't help? Where would you open the system to use this for the Q7 TDI (2015)? The Liqui Moly instructions say to open the air system "as close as possible to the engine". I suppose this could help clean the throttle body and manifold. Would it help anything else?
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Effect of speed on fuel mileage TDI Q7
