My apology to some members who have seen this question posted before
.
The EPA originally had posted the fuel Economy for the Jaguar 1996 XJS :

Combined MPG:18 MPG
City MPG:16 Highway 22

I have never had my mileage above 15 MPG combined.


My low mileage XJS has been kept to a high degree of maintenance and I had hoped that this would also provide me better fuel economy.

My, Tires, brakes, bearings are new.
Throttle, EGR, MAF, oxygen sensors, spark plugs/ wires, fuel filter, air filter, oil and filter, transmission fluid, brake fluid, hoses/clamps, radiator flushed and temp sensor, tire pressure, vacuum hoses, Andy's bracket, ETC. ....all have been maintained and/or installed/changed.

Is there anything else I can do to increase my mileage other than radical modifications and/or have I missed something?
Is there anything I could to investigate and determine what can be done in reducing my fuel consumption?



Example: I was told the last week that if I change to synthetic oil, I would increase a fuel mileage a few percent.

 

In fort lauderdale you probably won't see much more than that. How much do you drive highway??

When I used to live on Georgia, even smallest roads to and from places that weren't in the neighborhoods themselves were 55-60mph. If you are simply driving around town from stop light to stop light, with speeds averages 35mph, you will never see those figures.

The AVG is an average between city and highway, you are mostly driving city. If you are doing anything but driving like a saint you probably aren't going to see 16mpg.

I used to mess about trying to get best MPG to entertain myself and got my 5.3 up to about 19. In Tallahassee I get 9-11mpg depending on how much fun I have.
I know you have more speeds and less cylinders, but how realistic are you being about the ratio of highway and city?
Have you ever put a specific amount in, driven on the highway at a constant speed, and then figured your mpg?
I am assuming the 1996 would throw you a light if it were running too rich or lean.

I would go run 5 or 10 gallons on the highway at exactly 65 or 70 and see what numbers you get back and decide from there if something must be wrong.

Am I reading 20,600 miles right or should that be 200k?

 

sidescrollin:
I use highway app. 50% so I had hoped my total MPG would be slightly higher.
I have not taken results from highway only since my average MPG has been balanced even if I had less highway use. I will do as you recommend next week and do a test only on high speed thoroughfare. And yes, I have six cylinder, XJ16 engine and I'm not sure how we can compare fuel use.

I have now 20,800 miles on black beauty. I'm the first owner that has used it as daily driver. It gives me the sensation of a new car. It just needed me to update it all for its age not so much for being driven...:icon_trophy

 

I was reading this very carefully, rather strange for me.

Then I found the problem, YA GOT 6 CYLINDERS MISSING.

My HE 5.3 does 26MPG (Imperial) on the road trips, and 18ish (Imperial again) around the 'burbs. We got dumb 50KPH 'burb speed limits which the V12 luvs, NOT.

That AJ16 should be running 10W40 Synthetic oil anyways.

The timing wheel on the front pulley can be tricked to give 5deg advance to the sensor, which will assist the economy somewhat. My 3.2 X300 is much better with that little trick being done.

We dont have very much "smog" junk on our engines, more like NONE, so maybe that does impact on your engines more than I realise.

 

FWIW I do about 80% highway driving and my combined average is about 17 mpg. I can average 20-22 quite easily on the highway but *any* city driving knocks the average numbers right down....in hurry

Cheers
DD

 

grant, he isn't talking imperial mpg figures

RobertL, how fast do you drive on the highway? Highway figures are always better but of course there is a point where it starts going back down. The high point on the XJS V12 is around 55 or 60, then it goes back down. The car is very easy to drive on the highway and if you aren't doing the speed limit you may be bring it down. Still that seems like it would be low.

Do the newer cars have a MPG calculator built into them like the older cars?
So your O2s are new?

 

I'd be very surprised if any difference could be demonstrated.

Agonizing over EPA numbers, especially old ones, is a waste of time. They were never meant to be representative of real world numbers, only to compare one car against another. Never forget, without the EPA we wouldn't have the acronym 'YMMV'.

 

Correct. Not real world. For example, the 'highway test' is something like 5 miles @ 54 mph. Real people drive at 70+ mph !

The purpose was to provide apples-apples comparisons from car to car, since each car was tested the same way

That said, the EPA estimates CAN be achieved IF you drive like there's an egg under the throttle pedal. Not just any egg. The thinnest-shelled, most fragile egg you can imagine. I proved this to quite a few customers over the years who insisted that there was something wrong with their cars

Cheers
DD

 

EDIT, nevermind, I don't read so good.

 

Very strange.

My AJ16 tends to stay in the 17mpg average range. Sometimes even 18!

 

Thanks: The next time I Change my oil, I will use synthetic.

I have installed the Andy bracket and it provide me the 5% advanced.


Difficult to translate from Imperial gallons (4.54 Litres) to U.S gallons ( 4 quarts)

 

[QUOTE=FWIW I do about 80% highway driving and my combined average is about 17 mpg. I can average 20-22 quite easily on the highway but *any* city driving knocks the average numbers right down....in hurry ...DOUG
Cheers[/QUOTE]



Thanks for your replies I'm getting a grasp of my incorrect assumptions.
I do not drive 55MPH highway.
I drive more in the range of 70-75 MPH. So realistically I am getting good fuel consumption
It still feels strange not receiving better fuel mileage. Because the car feels light, as if I was on a skate board
I forget I'm driving a heavy car-- 4000 LBS Gross weight.

 

[QUOTE=sidescrollin;1101258]grant, he isn't talking imperial mpg figures

I know, I was just too damn tired to go to the conversion table and do it for him.

Slightly better at this moment, so here goes.

Online Conversion - Convert just about anything to anything else

My 11.2L/100Kms is 21Mpg USA, or 26Mpg our scale.

My 15ishL/100Kph is 15.68Mpg USA, or 18ish Mpg our scale.

The PreHE (Sir Arthur) in my gagrae is half that Mpg on any day, thirsty sucker.

 

"Difficult to translate from Imperial gallons (4.54 Litres) to U.S gallons ( 4 quarts)"


Robert.
Everything has 'quarts', Its just a way of saying quarter. ie 4 make a whole thing.......Imperial or US gallon have 4 quarts. l think you meant to say.


1 Imp. Gal. = 4.55 lts
1 US Gal = 3.79 lts

 

I need a BIG JD.

Hanging Christmas lights = NO Jaguar work being attended to, and drinking time getting eroded.

Imperial to Non Imperial, simply NOT rocket science, its a Jag, they do what they do, and they always have. If economy is such a major issue to anyone, buy a Hyundai, or a Non Jaguar.

Some of my past Jags have DRANK the liquid, as have I, and some of the later ones are better. The AJ16 is "old technology" by todays standards and does pretty damn good for what it is.

Wife is still looking at that damn Bentley TurboR, and that is NOT a small slurper is any language.

 

My Lincolns were supposed to get 27 highway, and I can honestly say that I not only achieved that, but surpassed it pretty frequently. I had to drive like a responsible human being, but that usually wasn't a problem.

This was painstaking, and expensive. Constantly spent time making sure the Mark VII was in perfect tune, that the fluids (synthetic only!) were fresh, and that no "cheap parts" were used - no store-brand junk, no economy parts, no low-octane fuel from off-brand stations, none of that.

Was it worth it? Sort of. It was kind of fun to hit the F/ECON button on the Tripminder and show people that a 3,800 pound, V8 powered RWD luxury coupe could get the kind of fuel economy that their modest sedans were proud to advertise. It was kind of fun to roll around in a 20+ year old car that moved through the turns effortlessly and handled smoothly and quietly while someone else's five year old mid sized import creaks and clunks and squeals like a haunted machine.

As the years and miles passed, the fight became increasingly uphill. And, as mentioned above, any time at all in the city was hell for my fuel economy. I never made the advertised 18 mpg. Hell, 15 mpg was a win in my book.

Fuel economy has never been a selling point for me, though. I want my car to major in luxury and minor in performance. If they have to sleep through fuel economy 101 to do so, then so be it.

 

It is just engineered well, just because it feels nice and light and cozy and the engine doesn't seem to struggle doesn't mean it isn't using gas to do so. The suspension is really nice and doesn't really convey speed, so it seems very effortless, regardless of fuel mileage.