When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The XF is certainly a capable highway cruiser but as many users may already know, the 5.0L variant tends to be thirstier than less equipped, much less fun cars.
Having achieved 12mpg driving like a retard (or like I stole it like Big Will would say) and up to 24mpg cruising, I wanted to prove that an owner with enough self-control could go from South San Francisco to Orange County on a single tank of gas. I've done the trip before and had to fill up once, just shy of getting home which is ****ing infuriating.
On a hot 100*F+ Sunday afternoon, I set out to do the impossible on these eccentric machines - get good gas mileage. So what is the expected outcome? The 5.0L SC engine is supposed to get 15/21mpg (city/highway) but I usually average 16-18mpg.
The end result is somewhat surprising. I pumped my tires to their max rating of 52psi which is probably not recommended. Using a combination of shifting to neutral (to maximize gravity, decrease internal resistance from engine braking) and really boring driving, I was able to get 26mpg (calculated from fill-up pictured below) but the onboard computer reading of 28mpg is still more satisfying to lie to myself about.
If you've been able to get similar mileage or think something might actually be wrong with my engine, let me know! Otherwise, I've noted the details of the trip below.
Methodology:
- Shift to Neutral going downhill and coast with minimal braking
- Stay at or below 2k rpm
- Freeway only driving (trip starts at gas-station and ends at gas-station)
- No pit stops (OK, I took ONE stop for 10 avocados for $1 )
3/4: 127 miles, 26.8mpg 1/2: 210 miles, 26.8mpg 1/4: 310 miles, 26.8 mpg// 340 miles, 27.5mpg (gauge went up again after coasting so two readings) 1/8: 404 miles, 28mpg (No Low Fuel Warning came on at this point)
Calculated Mileage:
(404 miles)/(15.51 gallons) = 26mpg
Pictures:
Speedometer reads +3-4% due to larger tire diameter on XFR/XFSC (not sure if this calculates into Odometer readings also)
Tank goes below 1/8 but no Low Fuel warning comes on
ECU calculates 28mpg but my own calculation shows this is actually closer to 26mpg
Freeway only miles
15.5gallons to fill to full. Made it to a gas station with just a bit to spare
Last edited by mechanicalturkey; 07-18-2017 at 04:40 AM.
28.4mpg over 90+ miles was basically all highway miles.
My normal experiance is:
Week day consists of 40 miles (round trip) to and from work. It is about 50-50 highway and city (35-45 speed limit city, not too many stop lights/start-stop helps) I average around 22mpg daily. I would think the average speed for that mpg is around 40mph.
BUT, when I am feeling aggressive, I can expect around 12mpg city
28.4mpg is incredible. I wonder if they have better gas quality out there in Iowa or if there might be other factors improving your mileage. What tire size are you running?
EDIT: What is this ECO mode you have on your MY2013? On some newer cars, they have the cylinders shut off. Also, your NAV button placement is amazing - I wish the pre-facelift models had them as well.
I get exactly same ( 30mpg or 7.8L/100km ) when crusing at 102km/h for a couple of hunderds kilometers(no agresive overtaking) with old and ineficient XF 4.2 SV8 ( SC in US)
to drive this car is actualy cheaper than any other xf, as I use LPG (it takes 22MPG on same cruise of LPG which converts to about 44MPG. not bad for a 400+ car)
Once I did 1300km(800+ miles) with single filling of both tanks.
When I drive REALLY agresively i got around 10MPG on gasoline and 9MPG on LPG) Jag V8 can be veru economical if driver economicaly, but if you push it drinks
I have a gas station at the exit of my subdivision that has 91 octane (no alcohol). That is all I ever use.
My trip home was 30mpg at 70mph average over 90 mile trip.
The 5.0SC models don't have an ECO mode. It does not have "displacement on demand" or anything like that. It does have start/stop but that does nothing on the highway.
I am running the stock tire/wheel size. 255/35/20 front and 285/30/20 rear.
In the famous words of Jeremy Clarkson when commenting on fuel mileage of a Prius vs. M3.
"It's not what you drive that matters, but how you drive it"
144,593 miles - Now that's something worth writing home about. Congrats
Any major bumps along the way or good maintenance pointers on how you got there. I'm only halfway there.
Haha @nsl1, thanks. I guess the big ticket item on these engines are:
1. Water pumps and surrounding plastics are known to fail so should definitely be replaced
2. Supercharger coupler will go bad (will need to be rebuilt or replaced)
3. Transmission replaced at 120k because Jag claims they are sealed-for-life (with proper transmission oil/filter changes every 50-60k this should never be a problem. should run around $300 for parts)
4. Replaced the radiator fan but not aware if this is a common problem or not
5. Some of the lower suspension pieces that had torn seals and bushings so they were swapped at 100k as a precaution. Easily visible on a lift
5. Swapped diff oil to redline heavy at 130k
6. 100k tune-up: supercharger belt, accessory belt, spark-plugs
7. Oil changes every 7k full-synthetic (the filters are insanely expensive though ~$40)
8. Timing chain will eventually stretch and go bad even with the tensioner - haven't replaced it yet myself but want to.
Not sure if I missed anything but I'm sure there's plenty on the forums
The XF is certainly a capable highway cruiser but as many users may already know, the 5.0L variant tends to be thirstier than less equipped, much less fun cars.
Having achieved 12mpg driving like a retard (or like I stole it like Big Will would say) and up to 24mpg cruising, I wanted to prove that an owner with enough self-control could go from South San Francisco to Orange County on a single tank of gas. I've done the trip before and had to fill up once, just shy of getting home which is ****ing infuriating.
On a hot 100*F+ Sunday afternoon, I set out to do the impossible on these eccentric machines - get good gas mileage. So what is the expected outcome? The 5.0L SC engine is supposed to get 15/21mpg (city/highway) but I usually average 16-18mpg.
The end result is somewhat surprising. I pumped my tires to their max rating of 52psi which is probably not recommended. Using a combination of shifting to neutral (to maximize gravity, decrease internal resistance from engine braking) and really boring driving, I was able to get 26mpg (calculated from fill-up pictured below) but the onboard computer reading of 28mpg is still more satisfying to lie to myself about.
If you've been able to get similar mileage or think something might actually be wrong with my engine, let me know! Otherwise, I've noted the details of the trip below.
Methodology:
- Shift to Neutral going downhill and coast with minimal braking
- Stay at or below 2k rpm
- Freeway only driving (trip starts at gas-station and ends at gas-station)
- No pit stops (OK, I took ONE stop for 10 avocados for $1 )
3/4: 127 miles, 26.8mpg 1/2: 210 miles, 26.8mpg 1/4: 310 miles, 26.8 mpg// 340 miles, 27.5mpg (gauge went up again after coasting so two readings) 1/8: 404 miles, 28mpg (No Low Fuel Warning came on at this point)
Calculated Mileage:
(404 miles)/(15.51 gallons) = 26mpg
Pictures:
Speedometer reads +3-4% due to larger tire diameter on XFR/XFSC (not sure if this calculates into Odometer readings also)
Tank goes below 1/8 but no Low Fuel warning comes on
ECU calculates 28mpg but my own calculation shows this is actually closer to 26mpg
Freeway only miles
15.5gallons to fill to full. Made it to a gas station with just a bit to spare
Hi mechanicalturkey please how do you calculate your MPG manually???
07-18-2017, 04:36 AM
28MPG on 5.0L Supercharged (w/Proof!)
