From the NGK website;

Iridium IX®

The Spark Plug
Serious Enthusiasts Rely On

Designed specifically for the performance enthusiast. Iridium IX® offers extreme ignitability, improved throttle response and superior anti fouling

* Fine Iridium tip ensures high durability and a consistently stable spark
* Iridium alloy has extremely high melting point, perfect for today’s high-tech, high-performance engines
* Trivalent Metal Plating - superior anti-corrosion and anti-seizing properties
* Outstanding acceleration, high fuel efficiency and durability
* Ultimate design, technology and performance.

I've heard that plugs can make a difference on several forums and from techs...across all brands...but it is negligible, 1 maybe 2 MPG's...

Of course it is all hearsay and your point is valid from that perspective...but I do know that car manufacturers are more concerned with a profit than anything else

 

The factory plugs are good to 100k

 

Fresh plugs dont hurt and w/ new plug advancements it can only be better than worst.....thus why better fuel burn, spark, fuel mileage and power

 

All brands claim the same thing, classic marketing hype at it's finest. The additional cost for an OEM to install 'the best' plug to gain that 1-2 mpg would be mere pennies.

Chrysler pays a total of 0.34 cents per plug for the Viper engines.

 

They use the iridiums to get a particular type of burn. You can read about these things if you do some research about how they work. Those plugs cost more than the older type so Jaguar would not fit them unless there was a genuine reason!

 

Not to argue, but I spent 31 years at an aircraft engine OEM in the design, manufacturing and field support areas. Part of the certification process was to demonstrate the ability to shutdown and relight the engine at altitudes of over 30,000 feet. Ambient temps were in the area of -40 to -50C. Other testing included bird, water and ice ingestion.

We tried hundreds of different types of plugs going from basic steel to the most exotic of materials, with all sorts of electrode design configurations. In amonst this was a similar program trying different types of ignition units, some giving off enough energy that it melted holes through the plug walls.

Made no difference whatsoever.

As stated before, a spark is a spark is a spark. A plug simply lights the fuel/air immediately adjacent to the spark. The spread of the flame front through the rest of the combustion chamber has everything to do with the engine design and nothing to do with the plug or the spark that's now long gone. Here's a simplistic example- the temperature of your BBQ does not depend on what type of spark ignited the fuel.

Iridium or platinum plugs are used simply for extended durability. Cars are required to stay within certified smog limits for X number of miles. Standard steel plugs don't last long enough to meet that requirement.

 

Were those piston engines which were essentially similar to those used in the jag (STR only if you like)?
Were they burning gasoline (as used in cars)?
Were emissions of relevance? Were misfires?
How much emphasis on mpg was there?

 

Yes, a spark is indeed a spark. I also have over 35 years of experience in caring for my vehicles (no airplanes, though). I for one will vouch for the superiority of iridium plugs. They burn cleaner, their tips stay much more intact and pristine, and some of them will go for the life of your vehicle. I pulled the factory set of Denso iridium plugs out of a 2000 Lexus RX300 at more than 120,000 miles just prior to selling it. The owners manual called for a plug change at 120,000 miles and I did it just as a selling strongpoint for whomever would buy this vehicle from me. But those factory plugs looked brand new and I really believe they would have easily done 200,000 miles as long as the fuel system was properly maintained. Had I kept the vehicle, I would have slid those factory plugs right back into place....

That being said, Denso and NGK lead the league by far in terms of iridium plugs. The factory iridium plugs in our 2005 S-Type 3.0 appear to be Motorcraft (which makes perfect sense given the Ford Duratech engine) and while they looked good when I pulled the easy-to-get-to drivers side bank for inspection at somewhat less than 40,000 miles, I will indeed change them at 100,000 miles per the owners manual assuming we keep the car that long. But I'll install a set of NGK iridium plugs at that time and that will be the last set of plugs this S-Type will ever need....

 

Hi,
The simplest and best ways to improve fuel economy is through practicing efficient driving techniques: moderate acceleration, drive at the posted speed limits, avoid/combine short trips, anticipate traffic to avoid unneeded stops and idling, not using cruise control when going uphill, etc. Use your instant mpg readout to teach yourself to maintain your travel speed at the highest mpg readings. To learn more about fuel efficient driving check out websites such as www.ecomodders.com, www.gassavers.org, www.cleanmpg.com . These hypermiling websites have a lot of great information on how to maximiize your vehicle's fuel economy. "Modify the nut behind the wheel" as they say.

As the OP was looking for vehicle modifications that improve fuel economy, I would recommend upping the tire pressure to the sidewall maximum to reduce rolling resistance. I have been running my tires at 42 psi for the past 20K miles and while ride is harsher, handling and tire wear are fine. I have over 76K miles on my original tires. Check your wheels for brake drag and fix it if its excessive. Insure that your wheels are balanced and aligned.

Keeping your car well maintained is critical but you won't find any significant improvements from using touted sparkplugs or air filters. Don't waste your money on snake oil products like HHO generators, magnets, intake turbulators etc.

Modifications that have a proven positive impact are aerodynamic modications and reducing weight. Aero mods: lowering the vehicle, grille blocking, passenger mirror removal, full belly pans. These changes work best at higher speeds but do make a noticeable difference. Weight reduction is less noticeable but still has a positive effect.

I am somewhat of a fuel efficiency buff and keep fuel logs for all my vehicles. I have achieved a best tank average of over 36 MPG and have a lifetime average of over 27 MPG in my 2000 S Type 3L SE. The mods I have done are 42 PSI tires, Grille blocking over the uppergrille opening and about 1/2 of the lower grille openings, R side mirror removal, front wheel deflectors and keeping unneeded stuff out of the trunk. I'll probably add a streamlining panel under the engine to further smooth air flow under the car. I made all my aero mods and they are easily removed if I need more radiator cooling airflow or need to use my foglights.

Some people will disagree with my efforts which is fine, I have a thick skin. The S Type is a great car; beautiful, fast, luxurious and efficient. I hope to enhance the efficiency without degrading its other qualities. This is what has worked for me. If you drive smart, keep your tire pressures up, and keep your car well-mainbtained, sleek and light you will be rewarded with good fuel economy. I hope you find my suggestions to be helpful. Please let me know if you want more information on getting the most fuel ecionomy out of your Jag.
Best wishes , VMV

 

This has this "SPARKED" some serious debate here....

 

VMV,

76,000 miles on a set of tires installed on an S-Type is quite an unusual achievement. What is the make, model, and size of your tires?

 

Even if I said yes to all those questions, I doubt you'd accept it. I'm not going to argue.

Please buy a set of the plugs, do some honest blind testing against any other set of plugs and let us know. Thanks.

 

Hi Jon,
I have the original Bridgestone Turanza 225/55R 16's on my Jag. They are pretty close to the end of their service life but I hope to get 80k out of them before I'm forced to replace them. I'm lucky to live in an area with no snow, minimal ice and not much rain, otherwise I'd be changing them now.
Best wishes, VMV

 

Never would have believed that a set of Turanzas could have done that kind of mileage on a relatively heavy car like the S-Type.

I've done a lot of research on the next set of tires I'll pick for our 2005 S-Type 3.0 (235/50/R17). I want a combination of long treadlife, excellent wet weather handling, a smooth ride, and some ability to get around in moderate snow (although I expect our S-Type will always sit out the snowstorms - it has thus far).

I'm leaning towards the Dunlop SP Sport Signature. The new Continental ExtremeContact DWS is also on my list due to its good reviews, but I believe its sidewall may be a bit too soft to allow it to achieve high mileage....

 

Hi Jon, Thanks for sharing your tire research. The Turanzas have been pretty good all-around but not very quiet. I'll be doing some tire shopping soon so I'm interested in hearing which tire you decide to go with and how you like them.
VMV

 

The Turanza line gets punished for its loudness by a lot of folks who buy them on many different types of cars. I had the Bridgestone G019 Grid tire on my short list for our S-Type, but three different local tire vendors have warned me about the noise after only 10,000 to 15,000 miles with those tires. So I scratched them off my list.

Unless my research changes, the Dunlop will be my choice. It carries a 60,000-mile treadwear warranty compared to the Continental's 50,000-mile treadwear warranty. And around here, a set of Dunlops will cost more than $100 less than a set of Continentals. I'll benchmark with tirerack.com and then work my buddy at Discount Tire to get the best deal....

 

Excellent write up...thank you for sharing...

 

There's really only one way to accurately measure your own car's mpg., and that's to fill the tank full to the brim, note the mileage on the clock, do your driving for a few days or so, fill up again to the brim and note the miles covered. Simple matter then to work out the mpg by dividing the miles covered by the gallons consumed. (I use a calculator kept for the purpose, I'm not good at arithmetic. In UK divide your litres by 4.55 to get gallons). Remember american gallons are 7 pints against british 8 pints, so US figures will look slightly thirsty. Computer calculations as to mpg are not always accurate, sometimes wildly inaccurate; the full tank-full tank method is the scientifically accurate one, only depends then on the accuracy of the mileometer.
If you want a car that's frugal, you don't buy a Jag. Even the diesel S-type likes its drink, about 25mpg in cold weather big city driving. Why? because Jags. are a heavy motor, approaching two tons imperial for the XJs. This is why you get the nice ride. And is a good car to have an accident in, if you must.
Can you improve the mpg? Yes, but a qualified yes. Assuming the car is properly maintained (tyre pressures, injector clogging fixed, proper engine oil etc.) the biggest fuel-saver is the driver, pure and simple. And how do you drive to get this fuel efficiency? Modestly is the answer. All big cities now have the "green-wave" computer controlled traffic lights, so if you drive at the right speed, the lights will let you through on green as you approach them. This is only one feature. As a driver, you have to realize that enthusiastic driving won't get you around any quicker. It'll just waste fuel -- fuel YOU have to pay for. You put kinetic energy of motion into your car by burning expensive fuel; every time you use the brakes, or even slow down, this expensive kinetic energy is being wasted in the brakes as HEAT. So don't put that energy into the car in the first place unless you absolutely HAVE to. This means approaching a red light modestly, and in such a way as for it to go green when you get there, without you having to use the brakes. Ok, it's not easy, but it can be learned. Do a check on your travelling time for each journey when driving in this fuel-saving way, and you'll be agreeably surprized that it's not taking any longer -- honest!
Leedsman.
p.s. Driving economically also reduces CO2 pollution simply by burning less fuel, so you can go around bragging if you want...