Apologies if I haven't found an existing thread that covers this, (I have looked! honest! )

So, I've had my S-Type long enough to cycle through a couple of tanks of fuel and I have calculated the mpg..

I have been filling up each time from the same pump at the same location and I have been using Shell V-Power. My daily commute is 36 miles, of which 30 miles is motorway. The other 6 is almost entirely a rural road.

I'm getting 22 mpg, this doesn't seem right, I understand that the manufacturers figures may possibly be optimistic, but this is a long way off what is stated in the owners handbook.

So, where should I start in trying to improve this, I was thinking of doing the spark plugs and filters, the car has 86K miles on it and has (up to the last two services) been well maintained. (I have my doubts as to the quality of the last 2 stamps in the book, and the last service has a note saying spark plugs not replaced)

Is a service as above likely to help? What else should I look at.

 

Agreed, a tad thirsty, more in the V12 area, than a V6.

Spark plugs would be my #1, followed closely by the air filter.

The grade of oil has a lot to do with fuel economy on these cars, and you are doubting the last 2 stamps, so maybe wrong oil, both quality and grade??.

Other things will crop up, but they are the main things that I can bring to mind at the moment.

 

Hi Wearlej,
Your consumption seems on the high side indeed. If your car is an automatic, are you sure that the transmission is locking up correctly and engaging 6th gear. There have been some instances where 6th gear fails to engage, which as you will appreciate, seriously affects the fuel consumption rate.
Maybe worth checking this out.
Regards,
Telfer.

 

Thanks Grant, I wasn't aware that the oil could be a factor, I'll definitely add that to my to do list. The guy I bought the vehicle from claimed he'd had the plugs done before selling to me (and furnished a receipt for 6 plugs in someone elses name) but I don't really believe that.

How is sunny Adelaide these days? (I grew up near Belair)

 

Thanks Telfer, I have checked for 6th whilst on the motorway, if I push the selector across to 5th it drops back a gear, I've also noticed if I have the s button engaged it will stay in 5th and not go to 6th.

 

If you're saying that 22 mpg is your average, it's not really that far off what other owners see. Weather conditions (temperature) driving style, traffic, hilly terrain and a thousand other factors can affect mileage tremendously.

Have a read here:

https://www.jaguarforums.com/forum/s...mileage-86059/

and don't forget to convert US gallons back to real gallons.

I'd suggest that you find an opportunity to get out on a straight level stretch of motorway and let the computer calculate consumption while the car is kept at a constant speed. I'd guess that you'll be pleased at the outcome. Note that any variations in fuel mileage due to oil viscosity will measure in the tenths of a mpg, so there's not likely much to be gained there.

 

I like and agree with Mikey's response.

 

My 3.0 has been averaging 21MPG for the last four years. That's up a shade over one MPG since I switched from 10W-40 to 5W-30. It likes that stuff much better. Note that do a bit more bimbling around suburbia than you, punctuated by relatively brief motorway jaunts.

 

Yes, I've already read that, given that most of the examples in that thread are from owners with the V8 engine, and I have the 2.5 V6 engine, I'm still concerned.

Even more reason to be concerned if a V8 is doing 22 miles on 3.78 litres, and my V6 is doing 22 miles on 4.54 litres

As I mentioned above, 30 out of the 36 miles I travel a day, is on a motorway.. So that opportunity arises every day, and no, I haven't been pleased by the outcome.

If 22mpg is what the car does, it is what the car does, but as I mentioned in my original post I wish to at least take whatever steps I can if it is possible to improve it.

 

Nice avatar! I tagged along on some fairly scary laps of the old pacific highway north of Sydney with Steve Bisley a few times back when I rode motorcycles (and lived in Sydney). He rides pretty quickish

 

I should add while I think of it, the onboard computer thinks the AVE MPG is 25, I've calculated it to be 22 from the amount of fuel used and the distance travelled.

 

So what does your instant fuel consumption read at that point? If it's still 22, yes you have a big problem.

 

Pretty consistently around 25 (which is what the car thinks the AVE is), sometimes jumps up to 30 or so on a downhill stretch. Sometimes drops down to 6 and I have seen it go to 99 when rolling down a hill with no throttle at all.
But mostly around the 25 mark.
This last week I have actually gone to the extent of logging everywhere I have driven, and referred to maps to calculate the distance travelled. That matched the onboard computer so that is accurate at least.

I'm spending christmas in somerset with my wifes family, so does anyone know of a good supplier down that way where I can pick up plugs/filters/manifold gasket etc?? My father in law has a shed, which I don't, so I'll do the work while I'm there.

 

My 2003 V8 non R would indicate 32-34 US gallons or under the same conditions, or 40ish in imperial gallons. Ouch. I'd have a look at the air filter immediately. Spark plugs usually work/don't work with no in between. Non-firing plugs usually set a code which you haven't mentioned.

 

How's your tyre (tire) pressures..that also determines good and poor mpg...

 

If you have OBD-II logging capabilities, it may be helpful to log LTFT while in cruise.

It will show whether or not the actual amount of fuel supplied to the engine differs from the amount of fuel the ECM expects to deliver to the engine for the given conditions as programmed into the default tables.

 

another thing to check is you dont have any binding brakes

 

YEP, "oils aint oils", as Sol used to say in the Castrol adverts of years gone by.

I run Penrite 5W/40 Synthetic in ALL the Jags, all year round.

Belair, mmm, we are north, and its been hovering 40+ for about a week, and now its 29 and raining, so Qld has moved south, but still good beer drinking weather.

Our 3ltr returned 7.8l/100km, on our last 1000km interstate run. This equates to about 36mpg British spec. The X300 (3.2) returns 9.9l/100km for the same trip, which is 28mpg, which is acceptable for that big car. The V12 HE returns 11.2l/100km, still good in my opinion.

Also I ONLY run our 98 octane fuel, and NEVER Ethanol blend (not common down here anyway). I did try our 95 as per the cars book, OK, but not as sweet as with 98, and economy does go down with the lesser octane.

 

Another thought!!
Also, check the tyre pressures, as the door will say one pressure (36kg) for example with two people and (38kg) for full load of four people and luggage. And another for 100 kph speed. Use the air pressure for the loaded car, as you do not always go in two's and your speed is probably over normal. Creates less friction to road and will handle better and tyres will last a little longer if stay below 100. The lower pressure is for smoother ride. Sure it may be a little more harsh ride, but may give you another mpg. If you like the car don't worry about the fuel, it'll take care of you in the long run. And yes, the higher octane fuel Jag recommends will induce better mileage and performance. My wife bought a new MINI Countryman S and the saleperson suggested REg fuel, well the fuel cap sticker said to use 93 High test and she got a whopping 2.3 mpg better.

 

My $0.02 - tyre pressures and brand of tyres and size - confirm you have the correct size tyres in place...