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12 vs. 6 Cylinder - gas mileage?

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  #1  
Old 03-28-2011, 11:38 PM
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Default 12 vs. 6 Cylinder - gas mileage?

i am thinking of adding to my jag collection and think my next one will be an XJS...but i am trying to decide which engine to go after the 12 or 6 cylinder...one factor is gas mileage, but i am wondering if there is much difference? naturally i am thinking a 6 would be better but what a well kept 12 won't it be close then?...any thoughts on which way i should go?
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Old 03-29-2011, 02:45 AM
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Also, I'd be interested to know the difference in fuel efficiency between the 5.3HE and 6.0.
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Old 03-29-2011, 04:25 AM
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You pretty much answered your own question, in a weird kind of way.

The 6 cylinder will be better maintained just because it is a 6 cylinder, which nearly any mechanic can work out, and the AJ16 is one reliable Jag engine, as is the bolt on stuff that goes with it.

The V12 will be a BADLY maintained beast for the opposite reasons, as most mechanics do not understand 12 cylinders, work on them under sufference, and do ONLY what it take sto get it out of the workshop, and the 5.3 had MANY,MANY issues basically built in, a lot of Lucas (Prince of Darkness) stuff, wiring that fried itself due to bad placement, so on and so on. Then OLD AGE comes into it also.

The gas mileage is subjective. My '85 HE gets around 16L/100km around the burbs, and 11L/100km on interstate trips. The X300 gets around 13L/100km in the burbs, and 9.8l/100km on the last trip. I miss the pure GRUNT of the V12 on the open highway, but all in all life keeps moving on, as does the 6cylinder.

My XJ-S took 4 years of PASSIONATE work by myself to get it to be as reliable as any other car, so much so we have travelled the whole coast road of Australia (very long way) in it 3 times now and NEVER been let down.

I would buy a 6ltr if I was making this choice today.
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Old 03-29-2011, 07:22 AM
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I agree with Grant as for which engine to buy. I just recently purchased a XJS and did a fair amount of research before the purchase. Most of the articles leaned towards the 6 cyl. engine for reliability, some even stated that the performance is close to that of a V12. As for gas mileage, if driven the same, the 6 should easily get better gas mileage then the V12, but neither are going to be great.
FYI, If the XJS your looking at has inboard rear brakes, check them completely, including the parking brakes. After I bought my 93 XJS, I found that the rear inboards were trashed, even thou the previous owner told me he had replaced the pads. I shopped around for a mechanic and got quotes of between $2500-$4000 for the complete job. I ended up doing the complete job myself, but it still cost over $1000 in parts alone (rotors, calipers, brakes, etc.). As you already know, Jag repair can become very expensive, but you don't want a $4000 surprise immediately after you buy the car, like I did.
Good luck in your search.
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Old 03-29-2011, 07:40 AM
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My '88 XJS 5.3 V12 got about 12/13 mpg in city driving and about 20mpg on the highway. With careful driving below 70 mph I could manage 21/22 mpg highway.

My '95 XJR 4.0 six cylinder gets about 12/13 mpg in city driving and about 20mpg on the highway. With careful driving below 70 mph I can manage 22/23 mpg highway.

My '87 XJ6 4.2 six cylinder got about 12/13 mpg in city driving and about 19 mpg on the highway. With careful driving below 70 mph I could manage 20/21 mpg highway.

Bit of a pattern, eh? :-)

In fairness I've often heard from others who manage better results. A 4.0 XJS coupe would be lighter than any of the above cars so it might do better.

Most people seem very happy with the 4.0 XJSs. I wouldn't mind having one myself. However, if the car will be used only for weekend pleasure driving I'd be tempted to to get a facelift V12. Those 6.0 V12s are a real powerhouse.

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Old 03-30-2011, 12:31 AM
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thanks guys...this is some great tips...i notice there are alot more V12 XJSs out there than the 6's as well...
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Old 03-30-2011, 03:26 AM
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Quote:
Originally Posted by Doug View Post
Those 6.0 V12s are a real powerhouse.
Yes, I remember you saying that in your buyers guide, but what of the 5.3? Is there that much difference? What's the 5.3 12 like vs the blower 6?
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Old 03-30-2011, 08:25 AM
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The 6.0 V12 and the supercharged 6 both have much more power...lower rpm power, specifically.

Also, after '81 or so anything with a 5.3 also got the tall 2.88 differential which only worsened the situation. Cars with the 6.0 or supercharged 6 got a 3.54 or 3.27 differential, respectively.

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Old 03-30-2011, 05:56 PM
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I've had both the V12 ('83) and the 4.0 AJ16 ('95 Convertible) and I much prefer the 6. I use my '95 as my DD and the car is dead nuts reliable, estimated gas mileage is in the 18-22/24 mpg range. It handles better, is more responsive, easier to maintain and repair. In terms of "livability" the 6 wins hands down. Just my two cents...
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Old 03-30-2011, 07:27 PM
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I've read up on this some. To me, the V12 has the mystique folks want but the expense nobody wants. From looking at prices on EBay the V12 cars have prices that are in the toilet and the "expensive ones" are around 5-7K. If you have to have the 12 I'd buy nothing but a car that someone else has spent a fortune on. Otherwise I would assume it is a turd.
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Old 08-07-2015, 10:03 AM
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Given the problems with notorious gauge issues on pre- and facelift models, and dodgy trip meters too, as best as I can figure, one may expect about 480-500 miles per tankful, or 770 kms/tankful. Would you agree with these ballpark figures ?
This assumes that the odometer is also accurate of course.. arrgghh
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Old 08-07-2015, 11:48 AM
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gerryxjs,

To get 500 miles out of a 4.0 convertible, you'd have to be doing 28mpg, which on average is way more than I get from my driving style!

At 23mpg which is my average over 13 years, you'll get a max of 410 miles out of a convertible.

Of course a Coupe has bigger range but you'll still need to do over 25mpg to get 500 miles out of a 4.0 Coupe.

Paul
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Old 08-07-2015, 04:58 PM
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My 1996 AJ16 engine consistently saw an average of 17mpg in the city and 23mpg on the highway.

Cruising at fair speed on a highway with no traffic over long distances, I did manage to get to a lot closer to 28mpg, but that's under ideal driving conditions.
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Old 08-07-2015, 05:35 PM
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Quote:
Originally Posted by dba-one View Post
To me, the V12 has the mystique folks want but the expense nobody wants.
This sums it up, if its going to be a weeked cruiser, you want the beast. You want people to gwak at the mess under the hood and look at you, trying to decide if you're a hero or a nutcase or both. The 6 won't cut it, you only live once, why live plain vanilla?
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Old 08-08-2015, 11:10 AM
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But, Warlock, I like vanilla ! :-)
I gleaned the miles/kms per tankful off either this forum or another, and based my calculations on a 91 litre tank (20 Imp.Galls or 24 US galls) however, I clearly made a blunder in my multiplication !! Obviously others were more optimistic in their mpg estimates etc.
Many thanks Paul, Vee and Warlock.


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Old 08-08-2015, 11:28 AM
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To address the OP's original question:

If my house had a garage, I would seriously consider the 6.0 v12. I like to spend time working on the car though.

I think you have to weigh the pros and cons of both the 12 and the 6. I can make a strong argument for both, but not for every person.

I find most repairs/refurbishments on the 6 easily done during the course of a day. I suspect many of my projects would take much longer on the v12, requiring a garage to finish work after the sun has set, rains have rolled in, etc.
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Old 08-09-2015, 06:24 PM
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Most sources I have read indicate that yes, the V12 has more grunt than the 6, and gas mileage is better with the 6 but not by much.
Against this, you balance the problems that can arise with the V12 more so than with the 6, and also the fact that the 6 is much easier to sort out, as you mention....
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Old 08-09-2015, 11:15 PM
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I wonder, though, how much longer the 6-cylinder cars will continue to enjoy their 'easier to own' reputation? Eventually age and mileage (and neglect) will start taking a toll....and some of the gloss might wear off.




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Old 08-10-2015, 08:16 AM
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My 1993 V12 6.0L averages 16 mpg (UK) around town.

On motorway runs it's closer to 18 to 20mpg .
Whilst this is my first Jaguar, I do wonder if some of the difference in reliability is due to comparing 1980s V12 with mid 1990s 6 cylinders.
I suspect later model , when under Ford ownership had better quality control and reliability.
My V12 is my daily driver. I part exchanged a Nissan R35 GTR for my XJS and love every minute I drive it.
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12, 53, cylinder, gas, get, jaguar, mileage, modify, mpg, take, v12, xj, xj6, xjs, xjs12



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