MPG What to Expect

[irishjag]

Now, just to say I didn't buy an XJR to lower my fuel bills!
However I look on the MPG more as an indication/measure as to how well the engine is running
Myself and the wife went off this weekend and did a round trip of around 120 miles, mostly motorway but a small amount of in town pottering.

From reading previous posts I had been expecting around 25-28 overall, but averaged 21.
Is 21 around what I should be getting?
Seems low to me and if so what could improve the engines running/performance?
There's no smoke and it's very smooth and quick so no complaints there.

Any suggestions welcome.

[J44EAG]

Chris,

21 is about right for round the houses and some dual carriageway or motorway work at sensible speeds. I have seen an indicated 31 when I`ve been exceptionally throttle conscious. Best MPG is on the motorway at no more than 56mph. Then you can see 27-28mpg. If you get the boost going at higher revs using the charger, then you can easily go down to about 18mpg.

Mileage can be helped by fitting a K&N 33-2273 air filter, cleaning the MAF sensor, changing the plugs, fuel filter, cleaning out the MAP sensor at the back of the throttle body and also having the car given Terraclean treatment. Terraclean is good at getting injector nozzles unblocked and spraying correctly. On a car that is new to you, that is the first thing I would be doing if I were in a similar position. Use of Cataclean in the fuel once in a while will help keep the cats as clear as possible. That is also a good preventative maintenance aide.

Helping an XJR breath more easily can also affect and improve fuel consumption if the car is carefully driven. Ridding the car of the standard power sapping intake manifold in place of a simple ali pipe helps reduce air drag at that point. Simple grind out mods to the top air plenum and cleaning out the throttle body throat will also help. Going further, removing the throttle body and reworking the top lip of the charger elbow will also improve performance. After that, you are into removing the charger and porting that out. Getting the charger off can be very challenging....Once it is on the bench a die grinder can give you a few hours of entertainment making the inlet side much less restricted which again helps fuel consumption.

Fitting either a 6% or 10% power increasing smaller charger pulley also helps get the torque coming in at lower throttle openings. again, this will help slightly with fuel economy provided you keep your right foot off large throttle openings!

Try a few of the easier standard service items listed above and see if you can improve consumption. 21mpg though is about par for the course.

[3.8etypephil]

Mine has averaged 20.6 mpg since acquisition, over a mix of town, fast single, and dual carriageway driving, dynamometer and private track performance testing, at electronically timed speeds well past the recording capabilities of the car's speedometer.
Used exclusively in Colchester's Liberal Dimwit anti car traffic system snarl ups, it manages just 13.8 mpg, according to the dash display, which seems reasonably accurate when checked with brim to brim re fuelling.
In normal daily use I expect 24 - 27 mpg, better if one behaves, so you should find that a little general fettling as suggested by Mike will offer worthwhile benefits.

[irishjag]

Mike and Phil

Thanks for the replies and suggestions
Seems I might be able to get a little better
The Cataclean/K&N filter/Terraclean seem to be the things to try for me first.

[J44EAG]

Agreed, Chris.

Also clean that MAF sensor hot wire mounted with two Torx head screws to the tube coming off the air cleaner box lid. Use spray carb cleaner, brake cleaner or acetone and a very soft small paint brush to remove any crud on the hot wire. Most dirt will be on the part of the wire facing the air cleaner.

You will note the air cleaner box lid is a pain to remove on the left hand side. You lift the lid on the right by the fixing clips, then when the lid is about 60 degrees off horizontal, you push the left hand side down to disengage from two tangs on the lower air box. The lid then comes off. At that point you will see the tangs are ¬ shaped. If you remove the short part of the ¬, you will be left with just a flat tang. That makes future removal of the lid much easier. Use a Junior hack saw blade to take off this un-necessary nuisance.

Mike

[irishjag]

About a week ago I got hold of a new K&N air filter,a bottle of Cataclean.
Fitted the filter, cleaned the MAF meter (didn't look very dirty to be honest, and the filter I took out (MANN) wasn't new but wasn't completely filthy), tipped in the cataclean when down to around quarter of a tank of fuel (although hard to be sure what was left as my fuel gauge is bonkers, a problem with one of the two senders from trawling the net)
Reset the trip computer and amazingly the average has gone up to 24.5 over the 150 miles or so since which i'm pretty happy with.
Haven't got the cash for the 'terraclean' thing yet.

So that looks like a good result, up from around 20 mpg and the 20mpg was with a good bit more motorway driving than I've done in the last week.
Thanks again for the advice and comments.

[J44EAG]

Chris,

Glad to have been of help. Cataclean really does work well.

Mike

[Manbearpig]

I'm a bit disappointed with the mpg on my newly acquired R too. 19 - 20 in mixed driving is not what I heard when researching (I have low expectations, and low to mid 20s is what I'm used to on all my cars). It psychologically precludes daily use!

I have used Cataclean to try and rid myself of the check engine light I have at the moment (now narrowed down to cats by a Jag specialist, to be done January). No change.

I have had the car smoke tested and fixed a couple of air leaks, no change.

Not sure about performance filters; I have fitted K&Ns before but always wonder about whether these dirty the MAF which everyone is so particular about cleaning. After all you are then sending the incoming air through oil which surely must mist the incoming air?

Terraclean - the smoke test guy does this as well but I'm a bit wary as it seems a bit extreme.

I love the car but starting to wonder if a V6 or TD would have been wiser!

[J44EAG]

Extreme blockages, require extreme clean out regimes. Carbon and oil bake can take some shifting especially after a few years of build up. Terraclean in my experience has proved most effective and I shall be repeating again in a couple of years time. My XJR became sluggish at 80k miles. A half hour session on the Terraclean rig proved most effective.

Cataclean is a most useful product. If you have a stubborn issue with fouled cats or dirty Lambda units, then you may need to repeat the process several times. If issues persist, then Terraclean is probably then the way to go. Cats can seriously block up over time. Lambda sensors can also become carbonised. I removed one myself the other day. It was well dirty, so I had the guy I was with clean it up. The trace on my Torque app certainly improved after that clean up.

Cats and Lambda units don`t last for ever and one has to be aware of that. The important thing though is to have a good verifiable and justifiable reason to change any of those components. Changing parts on an uninformed basis can prove unproductive and mightily expensive.

I have often heard people say they have changed cats and also complain of the cost. Usually they fit genuine OE units supplied by Jaguar. That isn`t always necessary although its fine if you can wear the big OE cost. My preferred method is to consult a specialist bespoke exhaust company such as Longlife Exhausts who are a franchised operation across the UK. You will be quite and pleasantly surprised at their costs, knowledge and level of service. You can also have a good haggle and see what deal you can achieve. This type of commercial organization expect that!

As regards Lambda replacements my experience to date has a couple of useful tips. Firstly, avoid any non OE Lambda units. I have one (after cat unit) here that was supplied for my car by Gendon. It was the wrong unit and they won`t take it back because I had the audacity to open the packet prior to fitting. What else can you do?! The unit fitted the exhaust stud but was too long and the plug detail and cable colours were wrong. I`m stuck with it. The next unit came from Manners, was a genuine Denso unit and the plug was the correct black colour, the wire colours correct and works as it should. It was nearly twice the price of the first unit but it worked first time. (Grey plugs on pre-cat sensors). The advice then is to buy from good suppliers such as Manners and stay OE Denso to avoid fitting difficulties.

As regards K&N type oiled filters and MAF sensors, I`ve had no issues. The secret is to keep the filter oiling down to a bare minimum. It does not need to be awash in oil. I clean the MAF on my XJR annually which is hardly necessary. Filter over oiling is a no-no. Done sensibly, there should be no issues.

The 4.2R and indeed the naturally aspirated models are the pick of the bunch. The V6 petrol is a solid unit but rather short legged compared to V8 versions. The diesel is only really suitable to long distance work. DPF units block quickly in short journey use. Maintenance costs can be eye-watering if problems occur. The diesel option needs an annual mileage of in excess of 30k when compared to the V6 petrol units to hit the break even line and then begin to show just a modest running cost saving. Diesel maintenance can be expensive, needs highly specialised garages and skilled operators and can be frustrating if multiple issues occur. Would you be better off with a V6 petrol? It would be the cheapest running of all options. With a diesel? Most certainly not due to potential maintenance costs overshadowing fuel savings and exhaust related issues.

What would I run? That would be a 4.2 NA if I wasn`t in a constant hurry. As I like a quick car, then the R wins without question. You will no doubt have read my numerous magazine maintenance articles and also looked at posts here. You will also have noted the run of electrical issues currently present and about to receive attention shortly. Most if not all of those issues also similarly affect the V6, V8 NA and also the diesel. So in that respect, all will suffer the same maladies given mileage, age, operating cycles and type of maintenance regimes applied. Sorry, what you are experiencing is the unique blend that makes the mark so appealing and charismatic....namely to have to own two Jaguars because one of them is bound to be in the garage receiving repairs! My XJR is due to go to Ray Brown next week...its falling to bits again!!

Mike K

[robv12]

Mid 20's is about right for an R 350/358

I do know Dave Marks gets 30 plus out of his 03 R on his long runs to Germany, and in fact a late night A1 run from here near Berwick to his place in Nottingham netted a 31.2 and not hanging about, I rode shotgun, so I know

That said I never get close to that

Many many things come into play, even if I drive like a wuss, and even a long run, then hand the car over to my partner, whatever she does the consumption goes down, MPG increases, her 180,000 mile 4.0 X300 LWB is sitting at 29.4 average, yes really 29.4

Good housekeeping is essential, we only use premium fuels, with an additive on a regular basis, correct and premium oils, correct Jaguar filters, plugs, coils all changed at below the specified interval . Tyres are correct spec, correct pressures, and no extra weight is carried other than spare wheel and essential tools

We have also taken to using EDT engine flush annually

http://www.edtautomotive.com/

Lots of claims, but on my 2008 358 tractor juice car, its was truly amazing, quieter , smoother, so much quicker in the mid range, emissions down, MPG up by about 15%, there is a feature due soon, see below

http://www.exclusively-jaguar.co.uk/spo ... utomotive/

As to which car you should have bought, well....

2.7 is OK if you are doing high miles, 20K a year or more, other wise you will have lots of issues, also expensive to maintain, a 3.0 is a good alternative, quick, quiet, loads about, not expensive, under a grand will bag you one now, unbreakable engine unlike the 2.7. We run one of each 3.0 locally, 2.7 long haul

3.5V8 , a gem, if you can find one, not a huge amount about

4.2V8, wonderful car, all the 4.0 V8 issues ironed out.. gone for ever... BUT, buy one an you will always wonder ... what's the full fat XJR like!!

so pay your money take your choice

[J44EAG]

Excellent material from Rob.

A couple more observations. The fitting of VVT units in later 350/358 models will make the car produce more low speed torque which means the loud pedal doesn`t need so much application to achieve the same effect as in a non VVT car. The availability of extra torque allows a higher gear to be selected earlier and further fuel economy achieved. Best fuel economy on modern cars is usually achieved at 56mpg with the car having changed up into sixth overdrive gear. I`ve seen 32mpg on my car which was in fairly standard tune at the time.

I fully agree with most of Robs appraisal. I`ve moved away from standard Jaguar air and oil filters to K&N units. My air filter change will result in little if any improvement economy wise. It does though have increased air flow through the element which comes into its own when the car is worked hard. The K&N oil filter is fitted as tests of this kind of filter showed a slight improvement in oil flow when compared to standard filtration media. Believe it or not as you wish. Another reason I use the HP1014 is that it has a 1" lug on the end of the cartridge which makes removal with a ratchet and socket exceptionally quick and easy.

Rob uses the EDT system to maintain engine cleanliness. This works along similar principles to Terraclean. Both preventative methods can only but help keep engine and internal component fouling to a minimum. Gummed injectors are one of the biggest curses. Keeping nozzles clear of fuel induced gum again helps with fuel economy.

I`m at odds as regards Super type fuels for the following reasons. Higher octane fuels produce more carbon and therefore fouling as well a potentially higher CO emissions at MOT time. Claims of enhanced engine cleaning are marketing bunk and are not substantive. Claims of saving "up to X mpg" gives the game away. I ask if fuels clean as they drive, why do some of us find the need to resort to EDT or Terraclean to dissolve gunked injectors? Take a look at some of the American Youtube vids to hear and see the reasoning as to why fuel companies are operating a con. Finally, why is there the need to feed excess octane into engines that were designed to run on lower grade fuels?

Mike

[robv12]

Lots of fuel arguments abound

What I do know is my devil juice 358 is best on shell super go go... supermarket fuel especially Sainsbury is awful, it gives lumpy running.. poor consumption and invariably ends up throwing the eml.. so avoid where we can

Our good petrol cars the same..but the petrol X Type hack gets filled with whats available... but still performs better on proper fuel

Additives.. we use Miller's for fuel

As for cleaning regime's we've not tried terraclean so cannot comment

EDT is an oil clean and engine flush using a light vegetable oil pumped in and vacuumed out.. the sludge that was drawn out had to be seen to be believed. New oil then goes in with a new filter. My oil stayed clean for ages even in a diesel

[J44EAG]

Interesting about EDT, Rob.

I tend to use two cans of Wynns Engine Flush added to the old and hot engine oil prior to evacuation with the front end slightly raised. I`ve an electric Clarke pump and pipes for down dipstick tube work. Like EDT, the Wynns does its internal irrigation act with aplomb. Even after just 5k miles, the amount of treacle within hot engine oil is incredible. A straight engine oil change could never achieve that on its own.

As is well known, my car also has methanol/water injection fitted. The vapourised gaseous meth/water concoction has two effects which are fairly marked. The 50/50 mix is sprayed down the plenum chamber into the low pressure area prior to the throttle body once the charger produces 6psi of system cut in boost pressure. This keeps the throttle throat clear of crank case gunk and also the MAP sensor which is located in the pre-charger inlet elbow. That together with the upper charger case, the cow-horn manifold, inter-cooler brick internals and cylinder head tracts are kept spotlessly clean by the methanol/water vapour. The same for the valves and piston crowns. That`s the good side of the system.

The slight downside side is that the vapourised gas content has about an extra eight octane units when compared or used in conjunction with either standard or super pump fuel. The water content cools the compressed inlet air/fuel charge and at the same time actively suppresses detonation. This allows extra ignition advance and allows more power to actively be released from the extra octane content. The down side is that more soot/carbon content appears in exhaust gas with not unexpected higher CO output. As the methanol/water system has an internal steam cleaning effect, that releases that extra soot and carbon/oil burn by-product into the engine oil. So with the methanol system in use, this means oil contamination accumulates faster than with a non methanol car. So be it. All this means in practice is my oil changes are now done at 4-6k mile intervals dependent on oil colour and contamination level seen on the dipstick,rather than at the standard recommended 10k intervals.

My preferred fuels are Esso or BP. I`ve avoided supermarket fuels although it is not unusual to see an Esso tanker on the re-fueling bunker stand.

Wynns, Millers, K44, various injector cleaner solvents, Cataclean, Seafoam etc, all have something to contribute together with EDT and Terraclean type processes. The difficulties arise when one tries to quantify in measurable terms, their true effectiveness. All one can do as an end user is note any apparent performance or economy improvements and detail them here for other owners to peruse. Apparent effects as a result of using additives will be less than for a vehicle that is gunged up, so what may be a brilliant find for one owner might not be so efficacious for another owner. All vehicles are differ for ever as soon as the leave a dealers forecourt and operate under widely varying conditions and maintenance regimes.

Mike

[Manbearpig]

Just a quickie - would any engine codes affect the mpg? After chasing down some leaks I still have codes 420 & 430 both banks "CAT inefficency".

The Jag indy diagnosed the CATs, presumably his machine can eliminate the O2 sensors?

I have the new (aftermarket) CATs in hand but dont want to fit them if it could be something else that could subsequently damage the replacements.

I also had my eye on a Longlife later on in the year when funds had recovered, would I be doing any damage by leaving the codes until then?

[J44EAG]

429 and 430, I know to be "cats out threshold limits". This is not always a cats problem. As I`ve previously said, I replaced a NSR Lambda due to those issues. So it had nothing to do with the cats. The issue was the fight between the upper Lambda (429) and the lower defective rear Lambda (430). Use of my Android phone, the cheap Torque Pro app and a bluetooth ELM327 chip allowed the issue to be shown on the oscilloscope on the phone. That set up is cheap as chips and allows zeroing of the codes which may or may not then reappear dependent on whether faulting continues. Running with the engine check icon or the MIL lamp illuminated can occur without damaging the car. They just signify an "electronic event" has occurred a few times and the car needs attention. Restricted performance requires more urgent attention...that means the car is in limp home to make sure management is temporarily reined in to prevent damage.The car becomes irksome and tedious in that condition and most drivers will want that gone as soon as possible.

The thing about this type of faulting is that until the issue is fixed (ie perhaps just one sensor) then one can expect several sometimes unrelated issues to suddenly and inexplicably materialise. Think of these faults and cods as similar as dealing with a naughty child. Forget rationality and logic...just see the issue as electronic idiocy which will remain until the car goes to the electronic physiologist! The fix is usually quite simple and is often only caused by one defective component.

A Jag Indy will have IDS/SDD dealer level gear to diagnose the car to a greater depth than is possible with either the Torque app or indeed our favourite iCarsoft 930i units many of us here use. He should have no problem itemising whether you have a cat or Lambda issue or a combination of both.

Before changing any components on a whim, always try to fix the issue by logical diagnosis prior to swapping out components. This is where professional help comes into its own. We can only do so much without professional gear and elevated knowledge. Sometimes we have no option but to reach out to the trade for assistance. Remember, these cars are complex and were never designed to be DIY serviced or repaired.

Mike K