I'm currently getting 16c/18h mpg which I don't think is terrible for a car this size with a V8. But short of slowing down, does anyone have any recommendations for moving these numbers even higher?

 

That engine is as efficient as it will get. Really comes down to adjusting your driving style. Otherwise, you would have to trade for a V6,

 

That sounds a tad low to me... I get 17/23 with my '11 XFR.

 

I use Shell Gasoline 91 octane (100% pure with no Ethanoil crap) and add 6 oz of Marvel Mystery Oil to every 10 gallons..My mileage is consistent in city at 20 MPG

 

That seems low for the highway, i get 25mpg at 75mph.

 

Forgot to ask, what octane gasoline do you use?

 

Driving style makes a huge difference. Don't mash the gas from a stop and keep out of boost on the highway. Also make sure your air filters are clean and your tires are properly inflated. That is usually good for a few mpg. Normally I would recommend swapping out fluids to higher quality brands (Redline etc) but from what I am reading here Jaguars are very particular about which oils and fluids they require.

 

I forgot to add weight reduction as a factor. The less weight the motor pulls the better your gas mileage. Don't haul around a bunch of junk in your trunk (Haha), remove spare tire, toolkits etc, you can also swap to lighter weight wheels. You will get the added benefit of making the car a little quicker too.

 

Wow! That's fantastic. I'm jealous of the green XF. That was the color I initially wanted but settled for the Liquid Silver.

 

I always use the highest octane available. Sometimes 91, sometimes 93 depending on the availability.

 

I feel stupid, but I honestly had not even thought about the weight factor. My trunk is jam packed with golf clubs and everything else. I'll give that a shot today. I'll also check the air filter. I assumed it was good because it is CPO, but that may have been a bad assumption.

Thanks for the help everyone!

JG

 

One thing I am surprised no one else has mentioned. Setting the DSC to track mode will certainly increase your fuel economy; that is if you tend to drive the car the way I do.
With the car using the brakes to limit wheel slip it is fighting your every attempt at having a bit of fun. Off or track DSC will keep the nanny from fighting you and it will save your rear brakes as well, tires not so much

 

If you're driving on public roads at speeds that cause the DCS to kick in, you'll soon be in jail or a ditch if you switch it off.

DSC has no effect during regular/legal driving.

Regarding octane rating, the cars achieve full performance on 91 AKI fuel. Use of anything higher just lightens your wallet and nothing else.

 

No and no.

The poster mentioned TRAC mode which is an additional feature on some vehicles. It is distinct from DSC. While the effect is minor, having traction control engage while accelerating from a stop will have an effect. And, it can engage at far less than legal speeds even without squealing tires.

As far as increasing octane is considered, it has been mentioned many times that the ECU will take advantage of the available headroom as determined by the knock sensors to remap the ignition advance curve to the optimal curve for the particular engine and individual driving style over time. The additional advance results in better gas mileage in terms of miles per gallon. However, the higher octane costs a premium. On the other hand, the increased cost of the higher octane fuel is offset by that increase in gas mileage with the result that the miles per dollar figure is often a tradeoff.

The effect of higher octane as noted above is repeatably observable to anyone who takes the trouble to data log the relevant parameters using simple ODB-II software. As such, the effects are independently verifiable as fact.

 

If the car is being driven hard enough to cause the DSC Track mode to engage, obviously fuel consumption is not a concern.

Regarding octane above and beyond Jaguar's recommended 91, show us your proof please, not just repeatedly claim that it exists. Your theory infers that the engine is on borderline conditions of detonation frequently enough that fuel mileage potential is compromised. I have my doubts that such conditions exist, especially under driving conditions where fuel consumption is paramount.

 

TRAC is distinct from DSC and ABS, although it occupies the same hardware space.

I have personally had TRAC engage coming off a red light with light mist on the road at light throttle. Absolutely no danger whatsoever. Meanwhile the energy is being wasted and the rear brake pads are getting used up. In other words, TRAC can and does engage unecessarily.

This is again your worn out old tactic of demanding "proof" when faced with logic and observation. As you are taking the opposing position, where is your "proof" to the contrary? It is disingenuous, at best, to issue demands where one is unwilling or unable to reciprocate in kind.

It is well known that optimal advance is one of the determinants of efficient operation of a gasoline engine. The "proof" can be found in any number of basic automotive texts at your nearest library.

When you state: "especially under driving conditions where fuel consumption is paramount", that is an attempt to muddy the waters.

It is well known that one of the main components of fuel consumption is accelerating from a standstill. Fuel consumption is much higher than the fuel consumption at steady state. As accelerating from a standstill is a frequently encountered situation in city driving, it certainly must be included in your stipulation of "where fuel consumption is paramount". Indeed, as fuel consumption is a cumulative average, all miles driven must be considered and not just some selective portion that is convenient to the writer. The "proof" can be found in any number of basic automotive texts at your nearest library. Or, since fuel consumption is a hot button question, any number of government agencies would be happy to prove they are of use by forwarding you a brochure or a url to the topic on their web sites.

As for the behaviour of the ECU, and its adapt to engine operating conditions including observed knock and typical demands of the particular driver, you can consult in particular Jaguar technical publications, or more generally, references on ECU design.

As for whether ignition advance even has an effect on fuel consumption, or whether Jaguar in particular even pays attention to ignition advance, you can read about real life experiences right on JF in the following thread:

https://www.jaguarforums.com/forum/x...nigines-66536/

Or, on the same theme:

https://www.jaguarforums.com/forum/x...emapped-66907/

As for obd-ii data logging, any one with the cheapest $20 ELM obd dongle can observe that same behaviour on their own vehicle at almost no cost. As I said, it is independently repeatable.

Finally, participation in a forum discussion is informal. Usually, the goal is to share knowledge. It is often non-exhaustive and the reader is expected to be able to delve further into things he does not completely grasp by further research. Perhaps by using search engines. On contentious points, it ought to be enough that the point is developed from sound foundations leading to reasonable conclusions. Demanding formal proof with citations acceptable to one particular participant is simply the type of obstructionism best reserved for situations like MSG-3 commitees. Or, for partipation at:

The Flat Earth Society - Index


+++

 

Mikey what are you the Jag ****? I am just stating that I personally saw a 1.5 mpg increase with switching to TRAC DSC
You would be correct that fuel consumption is not my major concern I had ECU Tuning group remap my ECU and increase the boost; my Jag is making @600 hp and getting better fuel economy numbers than Jimmy G. Turning the nanny down or off increases my fuel economy and my driving pleasure. Legal or not was not ever included in my statement. In TRAC DSC the nanny is still very aggressive with any lateral g's introduced it just isn't hitting the brakes every time I am hitting the gas.
Maybe you need to get behind the wheel of a newer XF before you assert your author-a-tay....

 

Damn guys, you make me feel really bad - I'm getting 14.7MPG in the city on my 2010 XF (5.0L). I'm using 91 gas and tried 94 - did not notice any difference...

Will try TRAC DSC trick and report if it makes any difference

 

@Plums- as suspected, you have no proof that the engine in these cars will experienced decreased fuel consumption with higher than recommended octane.

Quoting what happens on a different engines series (AJ16 and AJ6)that are known to be delivered to the owner in less than optimum state of tune is irrelevant. Any 1st year journeyman mechanic understands the potential power increases of optimizing an ignition advance curve, but also understands that an overly aggressive curve will either induce detonation or decrease the power output of the engine. There's a huge aftermarket making widgets to modify ignitions systems some of which are actually sound and functional. There's lots more that do nothing or make things worse

Neither of the discussions you presented involves taking a car in stock tune and using higher octane fuel as is being discussed here.

Theorizing that Jag delivered a current engine series in a similar detuned state is great- but there's no evidence to support this. On the contrary, there's dozens if not hundreds of posts by owners deliberately or inadvertently operating their cars on LESS than recommended octane and experiencing no loss in performance or mileage. My own experiments (which I'm sure you'll dismiss) using 87, 89, 91 and 93 octane fuel demonstrated no discernible difference. Notice that pumba has stated that using 94 made no difference.

@athompson.

Thanks for proving that Godwin (Godwin's Law) was correct.

A difference of 1.5 mpg due solely to TRAC DSC would mean that the system is interfering with operation of the vehicle almost constantly.

Occasional operation of the system, such as the example given by plums are insufficient in frequency or duration to affect average fuel consumption.

Other driving at excessive speeds around corners (when it's doing you a favour), there's no reason to believe that any such system would step in during conditions of constant or trailing throttle which forms a large part of driving.

This leaves the acceleration phase of driving. Again, if your driving style is aggressive enough to constantly have the nanny step in, and this is in turn genuinely affecting fuel consumption........................

 

Mikey, the DSC (Driving Stability Control) in the XF is also linked to the traction control. If you just take off in the rain with light throttle, DSC will kick in, doesn't mean you are in any type of danger.

XF has three different modes.
1. Traction control - loosens up the stability control a little, but not enough where you could light the tires up or get the car out of control
2. DSC OFF - It disengages computer inference even more. But, still it will not let you put the car into a slide per say.
3. DSC Trac off - Hold the same button down for full 10 seconds, it turns off stability control completely with 385hp on tap without any aids.


Will having DSC completely off yield high mpg under normal driving conditions? Absolutely not.

If you driving aggressively, then yes it's possible, as it will not cause an interruption in the momentum.