In reply to a message from Grooveman sent Wed 18 Jul 2012:
Dennis,
When I used my 4.0 litre car more than I do now to travel
greater distances it would consistently average 24.5 mpUKg -
that’s 20.4 mpUSg - over a mixture of highway and urban/town
driving on a complete tankful of fuel. I did many times
check the true consumption against the trip computer and
always found them pretty accurately matched so I have no
hesitation on relying on my VCM now.
All my driving is done in ‘Sport’ mode ‘enthusiastically’
(why have a Jag if you are not going to use it as intended?)
with full time aircon - by that I mean I set the climate
control and rarely touch it afterwards, whatever the
weather, just let it do its own thing.
Nowadays, driving shorter distances and less frequently (the
car only did 3885 miles in the past year!) I rarely see
better than 17 mpUSg and recently it has been as low as 15
mpUSg. However, I waste a lot of fuel shuttling cars around
in and out of the garage / driveway so that wreaks havoc
with my readings.
A little while ago when I thought the mileage was
deteriorating, I decided to replace the Lambda sensor which
was the original fit as it left Browns Lane. Cost me the
equivalent of nearly $100 USD for the OEM Bosch sensor and
I’ve now concluded that it made absolutely no difference at
all despite my earlier enthusiasm. I could have bought a
heck of a lot of extra fuel for that 100 bucks!–
The original message included these comments:
What is a ‘‘REALISTIC’’ fuel mileage figure for a 1989 3.6 XJ40.
I absolutely love my car and it’s a real joy driving and working
on. 140k miles and still near perfect compression, silky smooth
idle and acceleration. Always starts on the first turn of the key.
The only problem is that I get around 10-11 mpg. This is an actual
figure (the VCM says 9-10 mpg). All my driving involves short
around town trips with the air conditioning on 100% of the time.
So let’s hear from you and tell me your actual fuel mileage…and
please if you’re going to say 30 mpg or better go back and check it
again !
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In reply to a message from Grooveman sent Wed 18 Jul 2012:
why is it such a problem, to believe that these car s can have such
good fuel mileage? my 4.0 readily does over 30 mpg on the
motorway/highway and around 20-23 mpg round town/urban. I have a
photo I took a couple of months ago on the motorway, at 60 mph with
cruise on, showing 35.3 mpg!!
10-11 mpg, even on short distances, is certainly not good, given
that a modern bentley will achieve a bit better than that!!
depends on your driving style though I suppose and other factors,
like a boot/trunk full of junk etc. may sound and drive like its
running fine, but perhaps a tune-up is called for or something
thats slightly faulty, causing it to run a bit richer than it
should.–
The original message included these comments:
So let’s hear from you and tell me your actual fuel mileage…and
please if you’re going to say 30 mpg or better go back and check it
again !
Groove
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In reply to a message from 4.0sovereign sent Wed 18 Jul 2012:
Are you comparing like with like?
Don’t forget Dennis is talking miles per US gallon and you
are presumably talking Imperial UK gallons which are about
20% greater in volume than US gallons
Furthermore, quoting ‘instant’ MPG or ‘average’ mpg over a
short distance is pretty meaningless. I’ve seen 99 mpg on my
trip computer - downhill with my foot off the pedal! :-)–
The original message included these comments:
why is it such a problem, to believe that these car s can have such
good fuel mileage? my 4.0 readily does over 30 mpg on the
motorway/highway and around 20-23 mpg round town/urban. I have a
photo I took a couple of months ago on the motorway, at 60 mph with
cruise on, showing 35.3 mpg!!
10-11 mpg, even on short distances, is certainly not good, given
that a modern bentley will achieve a bit better than that!!
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In reply to a message from 4.0sovereign sent Wed 18 Jul 2012:
Same here 88 306 xj40 w/well over 200k gets low to mid 20’s city
and 26-32 highway. which is really the only reason I put up with
all the headaches that come with owning it. I would do a full tune
up and also clean the mass air flow. One more trick u might try is
to unplug smog pump unless of course you are due for emmision
testing might buy a mile or two diff. FYI by running that rich You
will deystroy the catalytic converters and muffler very quickly
which will cost 10times more than solving the fuel consumption
problem. little money now or alot later.–
88 xj6 saved from the grave
wellington CO, United States
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In reply to a message from Grooveman sent Wed 18 Jul 2012:
i am really in awe of those that get over 30 mph(us) on the hwy and
upper teens to 20 mph around town. I have owned my 92’ Sov for
about 18 years and the top mpg I ever got was 23.4. Granted I don’t
drive to get good gas mileage; 75-80 is common with the a/c on and
16.5-to 17 I consider very good around town. On the other hand my
94’ xj6 gets about 24.3 on the hwy and about the same as the Sov
around town. We all know that the ‘‘way’’ you drive makes a
difference but if I was getting 10-11 mpg around town, I think I
would park it!–
92’ SOV & 94
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In reply to a message from 4.0sovereign sent Wed 18 Jul 2012:
My urban mileage is terrible. The on-board computer shows
that in the past 1750 miles my average speed was 17 miles
per hour. The MPG is 13.
Get me on the highway for a long trip and I can do a 125
mile trip with a 30 mpg average. On shorter trips I can
easily get 25 mpg.–
The original message included these comments:
photo I took a couple of months ago on the motorway, at 60 mph with
cruise on, showing 35.3 mpg!!
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Well I have the two extremes.
I recently changed jobes and pior to starting the job I had to undergo
training.
This training was held across twon from where I live and included a good
measure of motorway travel. We have a 100kph limit so take that into
account.
Over a period of 2 weeks I was regulary getting around 27 Imp MPG.
Now that I am based closer to home the MPG has dropped a - little - to 10
MPG.
Considering that I am traveling less than 5 klms each way the car is never
getting hot hence the abyssmal figure.
And no I do not pussy foot around, when I get the chance I floor it
Regards Robin O’Connor
'92 XJ40 4.0 Ltr
Auckland NZ----- Original Message -----
From: “buddy 13” jameswade09@yahoo.com
To: xj40@jag-lovers.org
Sent: Thursday, July 19, 2012 6:17 AM
Subject: Re: [xj40] What’s your " realistic" fuel mileage
In reply to a message from Grooveman sent Wed 18 Jul 2012:
i am really in awe of those that get over 30 mph(us) on the hwy and
upper teens to 20 mph around town. I have owned my 92’ Sov for
about 18 years and the top mpg I ever got was 23.4. Granted I don’t
drive to get good gas mileage; 75-80 is common with the a/c on and
16.5-to 17 I consider very good around town. On the other hand my
94’ xj6 gets about 24.3 on the hwy and about the same as the Sov
around town. We all know that the ‘‘way’’ you drive makes a
difference but if I was getting 10-11 mpg around town, I think I
would park it!
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services and resources including Photo Albums, Event Diary / Calendar, On
Line Books and more !
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In reply to a message from Grooveman sent Wed 18 Jul 2012:
Hi, like others I also have a 1990 4.0l sovereign . When ever I
have done a freeway trip of say 200 -300 klm I have always returned
a trip computer calculated fuel usage of less than 12.5 litre/100
klm. It doesn’t seem to have mattered whether I used 91 or 95
octane . I should add that we have a 100 kl/hr limit on our
freeways. Around town , it has commonly been approx 18 l/100lkm
where most of the driving has been 60 kl/hr or under and a fair bit
of stop start driving.
Just recently I do believe that we have finally solved the riddle
of the code 44 check engine light comming on when retarting a warm
motor in the shopping centre car park.
I mention this because after many years and lots of money spent on
service, replacing sensors ,checking wiring especially the
management system grounds and the ECM etc it seems there were two
simple faults. Firstly , for some unknown reason, the manual
adjustment of the idle speed air control valve was fully shut off.
When this was adjusted as per the jaguar manual the difference was
really noticable , particularly the smooth idle and a small drop in
fuel usage around town.
Second, the nonreturn valve on the fuel pump was leaking making
starting harder without priming the rail first. This was replaced
the other day when the car was serviced. On the way home I reset
the trip computer. The 20 Kl continuous trip along the freeway
produced 10.6 /100kl. With town driving since then the AVE usage
has been slowly increasing . It is now 13.2 l/100 klm
I expect it will get to at least 16.
In relation to the ‘odd’ spark plug problem reported earlier by
Bryan. I have just fitted new spark plugs . They are long life NKG
Iridium 1X BCPR6E1X-11 . The gap is preset . Made in Japan.
They seem to be working well at this stage. I will keep an eye on
the indicated average fuel usage
Cheers all, freshy–
The original message included these comments:
I know I’ve talked about this before…but…
What is a ‘‘REALISTIC’’ fuel mileage figure for a 1989 3.6 XJ40.
I absolutely love my car and it’s a real joy driving and working
The only problem is that I get around 10-11 mpg. This is an actual
figure (the VCM says 9-10 mpg). All my driving involves short
around town trips with the air conditioning on 100% of the time.
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In reply to a message from Grooveman sent Wed 18 Jul 2012:
Grooveman
I have kept all mny records since I bouight mine about 12 years
ago - I maintain teh records every fill as I am of teh opinion that
one of the first indications of a potential problem can be a sudden
increase in consumption, albeit that the increase may be fairly
minimal if the records are kept a trend will immediately be seen -
as will an improvement after doing some maintenance
When I first bought the car it was at about 14 miles to the gallon,
over the years as I brought the maintenence together and learnt
more about the way these girls behave I now have average 19.5 -
20.5 urban driving in Singapore and 24 - 25 per gallon when I take
the car into malaysia and have a loing drive to Kuala Lumpar on the
expressways there
AC on all the time
There is defintely something wrong if you are at 10 miles per gallon
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In reply to a message from Nigel Snowden sent Thu 19 Jul 2012:
Well reading you all makes me dream. I haven’t had a chance
to use my car yet due to this braking problem that I wan to
fix but simply don’t have time to get to.
I look forward to posting my numbers. My car is beautiful.
Just wished I could use it. Sweet dreams.
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In reply to a message from Grooveman sent Wed 18 Jul 2012:
Reading this one have a question for anyone who know the answer
Reference has been made to US Gallons and UK Imp Gallons
I am sure that the trip computers for UK cars were set up for UK
Gallons and litres
Were the US cars set up for US Gallons ( I dont think so but may be
wrong)
1 gallon UK = 1.20095 Gallons US
1 gallon US = 0.8326738 Gallons UK
20 miles per UK gallon = 16.65 miles per US gallon
20 miles per US gallon = 24.02 miles per UK gallon
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In reply to a message from Nigel Snowden sent Fri 20 Jul 2012:
Nigel,
Correct - that’s why we must always specify mpUKg or mpUSg
when quoting fuel consumption, otherwise arguments occur!
It’s easy to recognise the litres per 100 km quoted by our
continental and some colonial friends and to save time I
have created some conversion lists on my note pad using this
useful tool :-
Reference has been made to US Gallons and UK Imp Gallons
I am sure that the trip computers for UK cars were set up for UK
Gallons and litres
Were the US cars set up for US Gallons ( I dont think so but may be
wrong)
1 gallon UK = 1.20095 Gallons US
1 gallon US = 0.8326738 Gallons UK
20 miles per UK gallon = 16.65 miles per US gallon
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In reply to a message from John Quilter sent Sat 28 Jul 2012:
In my 1990 XJ40 - 4.0l with 175,000 miles ( US Gals ) I get
City - 19mpg
Mix City-some-Highway - 21 mpg
Highway - 28 mpg
I live in Colorado USA and all of this driving is above
5,000 ft and up to 10,000 ft elevation and running on 86
octane. Once I go below 5,000 feet elevation I use Premium Fuel.
By the way the computer shows about 2 mpg below what I
calculate at each fill up and about 10% higher fuel use.–
New to Jaguar - Old to Cars…
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In reply to a message from Rocky Pilot sent Sun 29 Jul 2012:
Just to throw in my two pennyworth, I’ve just completed a
375 mile round trip of mixed urban and highway driving
(mainly the latter)in my 147,000 mile '91 4.0 litre,
cruising where possible at … (I take the fifth!) and my
trip computer records an average of exactly 25 mpUKg
(‘Sport’ mode with full-time A/C)
[That’s 20.82 mpUSg or 11.30 litres/100 km]
On the outward journey the VCM recorded 26.10 mpUKg before I
topped up the tank before the return journey. From my fuel
receipts, the actual consumption is calculated as 25.98
mpUKg - but I will post another thread describing why that
latter figure may be a little misleading! :-)–
Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Sun 29 Jul 2012:
You all seem to be doing well better than my 18.99 US MPG
over the most recent 1248 miles of mostly short trip urban
driving in my 1990 XJ6 4.0 liter with 66,000 miles. I use
89 octane and run the car at about 400 feet elevation with
the gearbox in normal mode and climate control system on.–
The original message included these comments:
[That’s 20.82 mpUSg or 11.30 litres/100 km]
On the outward journey the VCM recorded 26.10 mpUKg before I
topped up the tank before the return journey. From my fuel
receipts, the actual consumption is calculated as 25.98
mpUKg - but I will post another thread describing why that
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In reply to a message from John Quilter sent Sat 28 Jul 2012:
Hi all…
Glad to see my thread generated such a great response. I’m sure
fuel mileage is something near and dear to EVERYONES heart.
Also nice to see that we’ve discovered that a lot of the
differences in reported mileage is due to U.S. vs Imperial gallons.
Here’s yet another wrinkle that I don’t believe has been
mentioned…octane. I use ‘‘regular’’ gas which has a PON (pump
octane number) of 87. Is it reasonable to assume that since a
higher octane produces more energy that less of it is needed to
accomplish the same amount of work (moving your car)?
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In reply to a message from Grooveman sent Tue 31 Jul 2012:
Basically the higher the Octane number is the better it will
work with higher compression engines. Used to control knock
and ping ( pre-ignition ) And it only is a factor at higher
manifold pressures ( high throttle position ).
I live at almost 8,000 feet elevation, therefor I have no
need for premium fuel. Also if at low elevation and I keep
low throttle position then again premium fuel is not needed.
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In reply to a message from John Quilter sent Sat 28 Jul 2012:
Around Nashville, Tn I get 25-26.5 MPG (US). I’v erun 86
octane gas for over 100,000 miles in my car and changed the
head gasket about 12,000 miles ago. You could still see the
honing marks in the cylinder walls and the valves showed no
excess wear.
R,
Gunner–
Gunner 94 VDP 221K+ miles Kingfisher Blue
Hendersonville/Tn, United States
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