[xj-s] what is considered normal gas milage for a 5.3 v-12

XJ-S
1

The reason I ask this is because I don’t want to go looking for
trouble where there isn’t any. My 1986 5.3 gets around 12 to 13
miles per gallon in Fort Lauderdale, Florida city traffic. On the
road ( I95) at about 80 miles per hour I get about 15 to 16 miles
per gallon. Does this seem about right? Thanks.–
Juano
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2

In reply to a message from Juano sent Tue 17 Mar 2009:

That is about exactly what I am getting. Maybe we are both lacking,
though?–
1986 XJS
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3

In reply to a message from Juano sent Tue 17 Mar 2009:

I think that is about right.
I get 12-13 in town.
About 18-20 highway 65 MPH.–
1989 XJS V12 1984 Porsche 928S 1974 Triumph TR6
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4

Juano,

Sounds about right to me… I get about 11 in Fort Lauderdale on the city streets (I have a lead foot) and about 14-17 on the highway depending on whether I can keep it under 80 MPH… I’ll keep my eyes open for you!

Phil Sanfilippo
1991 XJ-S Classic Collection Convertible

My 1986 5.3 gets around 12 to 13 miles per gallon in Fort Lauderdale, Florida city traffic. On the
road ( I95) at about 80 miles per hour I get about 15 to 16 miles
per gallon.

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5

Juano wrote:

My 1986 5.3 gets around 12 to 13 miles
per gallon in Fort Lauderdale, Florida city traffic. On the road (
I95) at about 80 miles per hour I get about 15 to 16 miles per gallon.
Does this seem about right?

Nope, you’re using too much gas – unless you’re really thrashing the
car. When was the last time the oxygen sensors were replaced?

– Kirbert

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6

My 1986 5.3 gets around 12 to 13 miles
per gallon in Fort Lauderdale, Florida city traffic. On the road (
I95) at about 80 miles per hour I get about 15 to 16 miles per gallon.
Does this seem about right?

// please trim quoted text to context onlyOn all three of my Jags I’ve found that fuel usage goes up quite a bit at 70 mph or higher. Don’t know why that’s the magic number but there you have it. I’d drop 4- 5 mpg at 70 mph versus 60 mph with my XJS. Not quite so much on the XJ6 or XJR…maybe 3 mpg. I think Juano’s may be using a bit too much but not horribly so…and there are lots of variables. Worth checking the sensors, as you say, and a few other things, though. Cheers Doug Dwyer Longview Washington USA 1995 XJR From: “Kirbert” palmk@nettally.com Nope, you’re using too much gas – unless you’re really thrashing the car. When was the last time the oxygen sensors were replaced? Juano wrote:

7

Juano,

Congratulations! That’s better than I get and my V-12 is perfectly tuned!

Earl Kiker

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8

In reply to a message from Juano sent Tue 17 Mar 2009:

You don’t say whether it’s a convertible.

My mpg on the highway drops from 20 to 17 when the roof is down.

Yours is a little low on the highway number, but again you don’t
say what kind of highway driving you are doing.

The one maintenance item that really helped mpg for me, was getting
the injectors cleaned - this got me 1 or 2 mpg more on the highway.–
1990 XJ-S V12 Convertible, 1986 XJ6
Santa Clara, CA, United States
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9

In reply to a message from Kirbert sent Tue 17 Mar 2009:

Even though mine is an XJ (1986 5.3 V12), the engine is the
same, so these are my readings.
With light foot and moderate driving, no stops and constant
speed of around 60-70 miles/hour I can get as much as 22
miles/gallon - 11 lt/100km. The trip computer measures 25
miles/gallon but from what I have measured it’s about 10% off.

Aristides

http://www.jag-lovers.org/snaps/snap_view.php3?id=1191551908--
The original message included these comments:

My 1986 5.3 gets around 12 to 13 miles
per gallon in Fort Lauderdale, Florida city traffic. On the road (
I95) at about 80 miles per hour I get about 15 to 16 miles per gallon.
Does this seem about right?
Nope, you’re using too much gas – unless you’re really thrashing the
car. When was the last time the oxygen sensors were replaced?
– Kirbert

–
Aristides Balanos, 1986 XJ V12,VDP - www.e-psychi.com/jaguar
Montreal, QC, Canada
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10

In reply to a message from Kirbert sent Tue 17 Mar 2009:

Kirbert,

LOL

I would be overjoyed to get close to HALF that kind of millage.

My Average is about ONE-THIRD of what these people are getting.

PRE-HE Gas Guzzler

Darrell
1978 XJ-S–
The original message included these comments:

My 1986 5.3 gets around 12 to 13 miles
I95) at about 80 miles per hour I get about 15 to 16 miles per gallon.
Nope, you’re using too much gas – unless you’re really thrashing the

–
dlg78xjs
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11

dlg78xjs wrote:

LOL

I would be overjoyed to get close to HALF that kind of millage.

My Average is about ONE-THIRD of what these people are getting.

PRE-HE Gas Guzzler

Darrell
1978 XJ-S

Even a pre-H.E. should get around 12, and that’s US gallons, it’s a
bit more when using UK gallons. What are you getting?

– Kirbert

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12

In reply to a message from Kirbert sent Wed 18 Mar 2009:

Kirbert,

My car has never gotten anything close to the 8-9 MPG that the book
says,

My average is about 5-6 MPG

Darrell–
The original message included these comments:

Even a pre-H.E. should get around 12, and that’s US gallons, it’s a

–
dlg78xjs
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13

dlg78xjs wrote:

My average is about 5-6 MPG

You most definitely have something wrong with that car. What temp
thermostats are you running?

– Kirbert

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14

In reply to a message from Kirbert sent Wed 18 Mar 2009:

Unless you race the car or only drive in the city stop start on
short trips I’d have to agree with Kirby. My carbed E-type driven
at highly illegal speeds gave more like 10 mpg and normally 13-15
mpg (Imperial)–
The original message included these comments:

My average is about 5-6 MPG
You most definitely have something wrong with that car. What temp
thermostats are you running?

–
68 E-type OTS, 96 X300 XJ12, 94 XJR 5-speed manual
Cambridge, United Kingdom
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15

In reply to a message from PeterCrespin sent Wed 18 Mar 2009:

Yes peter,

You are right, the car is driven only 12 miles at a time back and
forth to work one day a week. So that probably does not help much.

As I drive a route that allows me such , I have a special road
coming home that I drive 5 miles at 100Mph. That probably does not
help either.

Now to answer the questions, thermostats are fine , gauges run
dead center, believe coolant temp sender okay as at least
according to forum , when it fails , fuel shuts off,

Now on to known problems yet to deal with, Vacumm advance shot,
screws holding distributor are siezed in same, broke one off (
end of project at least last year ) running with two left, check
advance with light, last year had some mech advance , at least
until the cat ate the tiing light. so not perfect.

Had some fuel issues this spring , that was on another post.

Car pulls strong from 0-120 so cant be too far off, have not tried
this year as not had the chance to take on the supper slab and see
how fast will run , maybe next month , will let you know.

Darrell–
The original message included these comments:

Unless you race the car or only drive in the city stop start on
short trips I’d have to agree with Kirby. My carbed E-type driven
at highly illegal speeds gave more like 10 mpg and normally 13-15

You most definitely have something wrong with that car. What temp

–
dlg78xjs
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16

dlg78xjs wrote:

Now on to known problems yet to deal with, Vacumm advance shot,

That’s a BIGGIE. Considering how fast you’re going through fuel, I’d
think the cost of a new vacuum advance module could pay for itself
pretty quick.

– Kirbert

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17

In reply to a message from Juano sent Tue 17 Mar 2009:

Well … if only I got that much. :frowning:

On the road at 70-80 mph I get around 15 mpg.

Around town when I drive it long enough and far enough, I get
around 12 mpg.

However … most of my driving is short duration trips, less than 5
miles, 10 miles maybe at most. Because nothing has heated up by
then … :frowning: … I’m really only getting about 8 mpg most of the
time tank full to tank full. Yikes!

Is there a way to by-pass that dreaded 15 minute fuel enricher
timer, and what negative effects would it have if that were done?

What does that operate off of? Coolant temperature sensor or
coolant level sensor? I ask because my coolant level sensor is
showing low coolant most of the time (but if I add coolant, it
spits it back out as it warms up, so I know the coolant is full -
just a bad sensor).

I’ve tried the trick of shutting off and restarting when the temp
needle moves up, but have not noticed a difference.

The only way I can make a difference is to drive it more. What a
novel idea! :slight_smile: Except that adds mileage to a relatively low
mileage car (1983 with 66,000 miles on it) and I’m trying to keep
the mileage low.

Any way out of that Catch 22 and improve mileage?–
The original message included these comments:

trouble where there isn’t any. My 1986 5.3 gets around 12 to 13
miles per gallon in Fort Lauderdale, Florida city traffic. On the
road ( I95) at about 80 miles per hour I get about 15 to 16 miles
per gallon. Does this seem about right? Thanks.

–
Jerry Peck, 83XJS/past-54XK140,54MKVII,59MK,60MKII,67E,72XJ6
Ormond Beach, FL, United States
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18

Jerry Peck wrote:

Is there a way to by-pass that dreaded 15 minute fuel enricher
timer

You haven’t yet? Just yank the wires off the thermotime switch at
the RR of the engine.

and what negative effects would it have if that were done?

Lessee, use half as much fuel, less engine wear, no, those aren’t
negative – oh, yeah: It’ll take longer for the heater to start
working well.

What does that operate off of? Coolant temperature sensor or
coolant level sensor?

Are we talking about the 15-minute timer on UK-spec cars? Because it
doesn’t work off either of these; the thermotime switch is in the
coolant manifold on the right side.

– Kirbert

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19

In reply to a message from Kirbert sent Wed 18 Mar 2009:

Kirbert,

Thanks, did not know where it was.

I’ll have to look for it and remove the wires.

Hopefully, my mpg will go way up - hey, 8 mpg to 12 mpg is ‘‘way
up’’ :-).

Thanks,–
The original message included these comments:

Is there a way to by-pass that dreaded 15 minute fuel enricher
timer
You haven’t yet? Just yank the wires off the thermotime switch at
the RR of the engine.

–
Jerry Peck, 83XJS/past-54XK140,54MKVII,59MK,60MKII,67E,72XJ6
Ormond Beach, FL, United States
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20

In reply to a message from Jerry Peck sent Thu 19 Mar 2009:

Kirbert,

Still do not know where it is, cannot find it.

Stumped.

Reading in Kirby’s book, and I see a location given for UK cars,
but what is ‘‘underscuttle’’?

Where on US left hand drive cars?

Thanks,–
The original message included these comments:

Thanks, did not know where it was.

–
Jerry Peck, 83XJS/past-54XK140,54MKVII,59MK,60MKII,67E,72XJ6
Ormond Beach, FL, United States
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