1. Having owned the car for a month now, I am trying to know what to expect from it. It is a 2000 3.0 Stype. The car runs absolutely smooth and has plenty of power. My issue is the gas mileage, according to the on board computer, is a bit over 16mpg. What should I be realistically be looking for? The only issue I am aware of, is the two buttons behind the J gate, I think one is for sport mode, don't appear to do anything and do not light up any lights in the gauge console. HELP

 

Wild Cat: What kind of driving are you doing... Puttering around town with multiple stops, or cruising along the interstate for extended periods?

Have you ever actually computed the mileage outside of on the trip computer at the time of a fill up?

 

I didn't think to manually figure it, so point well taken. 80% "puttering". I haven't owned a Jag for over 40yrs and in those days gas was so cheap who counted.. I must admit that after having a 4cylinder Hyundai as my DD for 8 years, it looks like I am spoiled. I asked service rep at the dealership what kind of mpg I should be getting and the response was 22-28 so he than said something is wrong. My belief is he said that to screw with my head and get the car into the $hop

 

Hi.
So, going in to Sherlock mode I deduce that you have an automatic gearbox.
You mentioned J Gate.
You need to research that, quite a lot.
If you have 'Sport' Mode selected on your box, you will have zero visual, um, visualizations.
Tiny little LED by the shift.
Figure it out Grasshopper.
Work around it; if you drive like a complete tool all the time then leave it in S mode.

 

Well being I am 81 and the fact that the car is a 3.0 not a 4.2, doesn't leave me much room to drive as a "tool"

 

I disagree!
The figures are quite similar, the V6 only loses out at the top end of the rev range in any gear.

Driving like a 'Tool' is very subjective; if you consider the pavement (sidewalk?) as part of the Highway, then you are a tool.

If you can't be bothered to look out of all of your windows, all of the time, twice; then yo are a tool.

Unfortunately, these are the sub-optimal creatures that we share our highways and byways with.

Also;
Be Happy.

I was quite happy being a Hobbit before all those film people came round...

 

Having been to "Hobbit Land" in NZ:, the hobbit movie set, I can understand how the film people screwed it up for existing Hobbits. LOL

 

Wild Cat: So back to your original question:

When it comes to measuring fuel consumption, it makes - ESPECIALLY for Jaguars - a huge difference, if you drive uninterrupted on a highway without traffic Jam or of you drive in town, low speed, frequent acceleration after frequent traffic-light stops.
As a rough guide, I found that city only could be double the fuel consumption of highway only.

So for a 3.0L S-Type it is totally normal - if you drive only around town to get 16mpg, which equates to 14.7 l/100km - it could actually be worse.

You should find a stretch of highway, where you can drive long distance at a reasonable speed. Our Australian speed limit is 110km/h on the highway, sometimes even just 100km/h. That is 62-68 mph. A bit slower actually means even less fuel consumption.

Before I started to trust the fuel consumption indicated on the dashboard (in the display, which was dubbed by a German car magazine "Maeusekino" when VW introduced it, when this feature was brand new back then (translation: Cinema for Mice)), I calculated the fuel consumption at many occasions by hand, after I filled up, and I found the display to be correct.

When I recently checked the consumption driving non stop a few hundred kms on the highway, I was surprised to get a fuel consumption of as low as 8.4l/100km = 28mpg on my 2004 and 2005 3.0L S-Types. That is a number I can only dream of when it comes to the fuel consumption on my X308 V8, not to mention the V12 XJS.

Also note that it makes a little bit of a difference, which grade of petrol/gas you are using. Here in Australia I got the choice of 95 and 98 octane for the Jaguars (91 octane is too low for those cars). 98 octane is more expensive, but should give you a slightly better consumption. When I measure my consumption above, I probably had a mixture of 95 and 98 in the tank.

For cars, which have a LPG conversion, the consumption figures are a lot higher (nearly 1/3 higher), but LPG is a lot cheaper than petrol, so that consumption-wise driving on LPG would be cheaper, but taking into account the meanwhile extreme conversion costs, it does not make financial sense anymore, unless you drive insane amount of mileages every year. (My Fairlane and Van drive on LPG - they both came with the conversion, when I bought them, and back then it made more financial sense, as the conversion was cheaper, the cost difference between LPG and petrol was bigger and as the quality of the LPG was heaps better. These days you can only buy extremely crappy LPG in Australia, which gives you a much lower mileage then in the good ol' days...)

 

Well my on board is showing me 17-17.5 so maybe I should be happy with that. I am going to take it on an 750 mile round trip next month so I will see what goes on then. The posted speed limits where I will be are mostly 70-75mph so I will probably run at +/- 80mph. I guess the proof of the pudding is in the eating

 

I assume that is 17-17.5mpg and not 17-17.5L/100km as both would make kind of sense...
80mph equates to 128km/h. If you drive that fast, you will probably not end up with 8.4L/100km (28mpg). It would consume more. I hope your 2000 S-Type also has, as my 2004 and 2005 S-Type the option of displaying the present consumption. Then you can see immediately the effects of different driving...

 

Yes it does have that option. What is really getting to me is my restored1981 BMW 635 is getting 18mpg in town and along with the fact that it is not broken in yet, and has a pretty modified motor along with short gearing. Oh well.

 

Expect a little worse MPG from a 2000 car than a re-engineered 2002.5MY-on. You've the older trans and older PCM (& without wideband O2s etc).

First, check your fuel trims in case they're off, though.

 

Well, Wild Cat, just for fits-n-giggles I checked my trip computer and the read-out was 16.7 MPG, for a mixture of stop-n-go driving with an occasional run down the highway to blow the cobwebs out. On a straight highway run, at 80 MPH I usually get 26-27 MPG, manually calculated at the time of filling up.

Around town mileage is not stellar, but it is a Jaaag...

 

One thing to consider: I'm not sure of the exact details, but believe the displayed MPG is based on the last several hundred miles of travel. It's quite possible your current fuel consumption rate is still affected by the previous owner. Did the car have any recent work performed? If the car spent any significant time idling or being lead-foot tested after repairs, that would skew the mileage computations, too. IIRC, disconnecting the battery also resets the mileage calculations. It takes several hundred miles for the computed value to settle down.

As others have suggested, definitely check the actual mileage, i.e. miles driven divided by fuel used. The dash display is something of a gee-whiz feature and may not be especially accurate. The computer has no way of knowing exactly how much fuel is used, for example. There is no component actually measuring fuel flow. Not 100% sure, but suspect the system computes fuel usage based on a known fuel pressure and injector "on" time. If fuel pressure is out of specs, for example, the computer has no way of knowing this, even though it will skew mileage computations. If an injector had reduced flow (for reasons unknown), the computer will command a longer "on" time to keep the air/fuel mix within specs per the O2 sensor. Even though the correct amount of fuel is actually reaching the cylinder (eventually), the computer mistakenly interprets this longer "on" time as extra fuel flow.

You could start by verifying fuel pressure is good. There's a test port on the injector rail, near the oil fill cap on the early V6. This test port looks like a valve stem for a tire. Connect a mechanical gauge. Ignition on, but not yet started, you should see 55 PSI to prime the injector rail. After engine start, you should see 40 PSI at idle. The computer adjusts the pump output to this desired value. If the sensor is off, the computer will happily adjust the fuel pressure to the wrong value based on inaccurate feedback from the pressure sensor.

Make sure you are using the correct octane fuel. Lower octane causes increased pre-ignition, but the knock sensors detect this and automatically retard ignition timing to protect the engine. In theory, the ignition timing is held right near the edge of knocking, for maximum efficiency. Fuel consumption increases with lower octane fuel because of this.

My '02 V6, driven conservatively by a cheap old fart, gets around 21.5MPG according to the handy dash display.

The button to the right, which looks kinda like a snail, switches off the traction control. You should see a message briefly displayed at the bottom of the instrument panel, and an amber icon illuminated above that. I think it automatically resets with each engine start, but don't quote me on that.

The button to the left is Sport mode for the transmission. This changes the shift points for better acceleration, and reduces your fuel economy slightly. The only indication is the red LED in the switch. It does not reset with each engine start. Might be opening a can of worms here, but the guy who rebuilt my transmission suggested using Sport mode. In normal mode, the shifts are smoother. This actually causes more internal wear as the shift process is deliberately slowed down, so the clutch packs have more time to slip. Sport mode reduces the slip time and causes slightly harsher shifts, but in theory the friction material should last longer.

 

I too have a 2000 3.0 V6 auto. I can tell you that mine drives beautifully, has only done 52,000 miles and has no problems with fuel trims. On a long run 25mpg is easily attainable. However, when pottering around town, she guzzles fuel at an alarming rate.
From what I am told, this is normal behaviour for my car. I love the car so much, I still prefer to drive the Jag instead of my much more frugal Citroen Xantia HDi.
Could it be remapped for better economy? Possibly, but I haven’t got around to fully investigating that. So far, I’m happy to enjoy it as it comes. I hope you get as much pleasure out of yours as I do mine👍😀

 

I think your response is the most accurate assessment and conclusion to my original post. I will have to learn to live with it's in town thirst. My car has 66K on it and drives as a new car so I will just enjoy it.

 

P.S. Your 1980s Beemer will have an unfair advantage over the Jag; it may have no Cats and it’s performance isn’t likely to be as compromised due to later emissions legislation. Many early 1980s cars perform equally as well as, or better than, their more modern multivalve counterparts. Emissions regulations have a lot to answer for, but they do help us breathe more easily.

 

One more thought:

Since the car is new to you, any idea when it last had new spark plugs and an air filter? If overdue, that would negatively affect fuel economy.

 

.Checking the airfilter is on todays list. As to the plugs that may be in the future. The engine has 66K on it and runs so smooth and goes so well, I can't believe the plugs and/or coils are bad. My understanding is the intake manifold has to be pulled to get to the plugs?

 

That is correct 👍. You will need four new inlet manifold gaskets (2 lower and 2 upper) and a fine flat file. The file is to level the plastic lower manifold that will have warped with age and heat.
In addition you may need to replace the odd plastic coolant pipe joiner that are easily snapped. Mine now has brass ones.
While you have the manifold off, it is highly recommended that you replace the rubber seals on the variable venturi flaps (I always forget what the proper name for them is). This will save you a lot of hassle with running issues and smelly oil leaks later on.
Also it is a good time to replace the cam cover gaskets, not forgetting the vvt grommets.
While you are at it, thoroughly check, and replace if necessary, the vacuum pipes and breather valve connections hidden under the manifolds.
There are also some coolant connections that can be easily accessed during this job that are prone to leaking (replace a pipe or two and a couple of rubber O-rings). See other posts for all of these suggestions in greater detail.
Yes, I know this starts to sound like a major overhaul when you were only expecting to replace spark plugs, but these are common-problem avoidance measures which can only be done while the manifold is off. These will also help you avoid the spark plug wells from filling with oil and causing a misfire, avoid inlet manifold and vacuum leaks (very common problem) and avoid inaccessible coolant leaks.

It is likely that none of these things will make your car run any smoother than it already is, but will almost certainly save you from lumpy running problems later on.