I've been getting some conflicting information regarding spark plug replacement. I have 41K on my 2001 XKR and have the original plugs. My local mechanic says, don't mess with them if the engine is running well (it IS running well). The Jag Vehicle Maintenance Sheet recommends plug replacement every 30,000 miles for supercharged engines (70,000 for non-supercharged). My Jag Dealer says they don't typically replace plugs until 60,000.

The original plugs are platinum, NGK PFR5G-11. These are now obsolete (not to mention 9 years old).

The Jag Dealer says they now use NGK IFR5N-10 iridium plugs. I know these last longer than platinum plugs. When I check compatibility with my car on various websites (NKG and Amazon), they say this plug is NOT compatible with my car!!

My first question is - why does the supercharger affect the life of a spark plug.

My second question is - exactly what brand and model # spark plugs have other XKR owners used?

Thanks!
Steve

 

I guess it could make sense that a supercharged engine would need spark plugs sooner. The point of a supercharger is to cram more air and therefore fuel into the cylinders. This creates more/better combustion and probably at higher temps, which would contribute to faster erosion of the plug electrodes.

I hope I don't offend any of our much more knowledgeable members with my attempt at explaining a supercharger

As to the kinds of plug, I'm interested to find out too, since I have 46000 on my R.

 

I just pulled up the Maintenance Sheet for the 2003 model year XK. There is a big change in the recommendation for plug replacement vs my 2001 Maint Sheet. Regardless of supercharged or normal, they recommend replacement after 100,000 miles. I'm GUESSING this may be due to the use of iridium plugs in these later models and their durability advantage over the platinum plugs that were installed originally in my 2001.

Maybe a Jag tech can confirm.

Jnpcello, you should be good for another 50K!

 

I believe that Jaguar recommends the 4.0 liter supercharged engine spark plugs to be changed at 30k miles.I did mine at 35K miles and did notice some improvement in preformance.The 4.2 engine is listed for a 100k miles.
The plugs that were in my car from new were iridiums and I replaced them with NGK (2341) PFR6G-13E .

Now I will just throw in my opinion,after plugs have been in a block with 100k miles on it is that you are taking a chance that they will be seized and a bit*h to get out.Just talk to the guys that are paid to remove them on cars with a 100K on thiem. What experience have others had?

 

I just confirmed with my Jag dealer that I can replace my plugs with the following iridium plugs:

NGK-IFR5N-10

I found these on Amazon for $4.40. Good thing too, because the dealer was going to charge me $30 EACH plus $200 labor for replacing the double-platinum plugs that are in my car now.

I'm having the dealer do the plug replacement. They will use the plugs I bring in from Amazon. Just curious though, how hard is it to do it yourself? Looking at my engine, I have no idea how to even access the plugs.

 

It is not very difficult and should provide a good bonding experience with your car if you are comfortable with some basic hand tools.

The spark plugs are under the rectangular covers bolted to each valve cover (one says Jaguar in silver letters, and the other is blank). Once you remove the covers you will see four coils on each side. Each coil is removed with two bolts and can be gently unplugged, or simply set aside with the cables. The coils are directly over each plug and they are attached to a rubber spark plug boot which must be pulled straight up.

Just make sure you retorque the new plugs with a torque wrench to spec., and a little antisieze on the threads would be a good idea.

If you come across any oil in the spark plug cavitiies in the valve cover, that is an indication that you need to replace the spark plug seals in the valve cover also to avoid problems down the road.

 

Steve,

You got a great deal on the plugs,on Partgeek they retail for $29.00 and sell for 11.94ea.

The plugs are easy to change,I purchased a spark plug socket with an extension that can be use in deep well engines such as the Jaguar.Take off the covers remove the coils inspect the plugs in the well and look for oil or other contaminates.Remove and replace the plugs ,torque per JTIS replace coils and covers.I put antiseize on the threads of the plugs and Dielectric Tune-up Grease on the boot that covers the plug.It took me 2-3 hours to do,but I do take a lot of breaks.

 

Iirc the 4.0 R engines use a heat range colder (6) from NGK instead of (5) which is used on the 4.2 engines.

This will not make a dramatic difference, however if you are seriously tuning (or have), it would even be better to go to 7 on the 4.0 cars (or at least stick to 6).

I also use the NGK iridiums, they do last pretty long.

 

And... do them one at a time. That way you don't forget which wire goes to which plug. Many years ago I made the mistake of pulling off all of the wires and replacing all of the plugs at once (on a different car). That was before the internet, and figuring out which wire went where took forever since I couldn't drive to the auto shop or library to look it up. Some lessons are never forgotten.

 

I only have the 2000MY maintenance sheet but they should be the same as 2001MY

bob gauff

 

Actually, you don't have to worry about this, each plus has an independent coil and lead. Each is identical, so you can take a whole bank off at once. I did mine a couple of months ago and it is a breeze.

I have a 1999 4.0L SC and I put these in... BKR6EIX11. I got them at RockAuto.

 

The PFR5G-11 is the NGK long life iridium plug for the 4.2 SC engine, its their best plug for this application. It's what I would use just because I hate changing plugs and use the longest life ones I can find. They do have a lower life iridium plug than this. I suggest changing them at 60,000 miles just to be sure they aren't seized.
At some point, time is the govening factor. When the car is 6 or 7 years old, I would change the plugs regardless of miles.

 

Avos, what is the source of this information? If my original plugs have a 5 heat rating (PFR5G-11), then shouldn't this be the correct rating for the replacement plugs?

 

The change in maintenance recommendations was probably made for legal or marketing reasons, not logical or proper maintenance reasons. At some point, which was probably around 2003, the US government changed the warranty period for all emission control related components from 60,000 miles to 100,000 miles. And crazy enough, spark plugs were considered part of this. Also, many of the luxury car makers started including all maintenance, which in most cases just meant rewriting the rules so it fell outside a warranty period.

Anyone who waits this long to do a simple maintenance item like R&R'ing spark plugs is crazy! As was already pointed out, the steel threads will seize in the aluminum heads before then (dissimilar metals cause this electrolitic reaction). Plus, the electrodes will erode from all that combusion. Performance and gas mileage will also suffer. And yes, additional boost pressures in a supercharged engine will accelerate this a bit but 30,000 miles is the most I'd put on any plug in any engine regardless.

My philosophy has always been to not buy top-of-the-line or gimic plugs but rather to replace them every year or so with quality OEM replacements. Cheap insurance, and by not buying super expensive plugs, I feel no guilt changing them out (and always keep a set as spares just in case).

Then again, I have been restoring cars for over 30 years and this work is so basic and easy I of course do it myself. Paying a dealer the mark-up on the parts as well as their labor rate is just not something I would even consider.

 

Thank you Dougboost!! Guys at least pull you plugs to check them out and if you are in that far you might as well replace them.A set of premium NGK plugs is less that a $100.

 

@Steve,

I have just checked the latest "Vehicle specification" sheet from Jaguar, and there it states that from the AJ27 engine (which you have) the same plugs/gapsize are used as in the AJ33 (4.2 engine). So then the heat range is the same now and can be 5. It was from memory that I mentioned it, and I think that befor the irridiums came the heatrange was 6 for the AJ27 engine (at least it was for the AJ26).

 

Its basic, simple preventative maintenance like replacing spark plugs which make a car drive many trouble free years.

Some other simple maintenance stuff that I would do judging the mileage, I would replace the fuel filter as well. Just a good measure and its a cheap job if you do it yourself. I would also keep an eye on the condition of the serpentine belt. They tend to crack and generally wear out around the 50k mile mark.

Its when the easy cheap fixes are neglected that can often lead to expensive damage.

 

Avos,

Just a question,I am using the NGK 2341(in a 2000 XKR) which is the recommended plug by all the application info from NGK and the engine performed like a fine watch after I installed them. What benefit would I gain by going to the heatrange 5. Or did Jaguar dumbdown to spec to simplify the dealers parts inventory?

 

If in doubt you could check your plugs to see how they look, that should give some indication.

I use also a heat range colder plugs (6) on my car, and my plugs look very good, so guess it will be alright.

You could also keep your plugs and add the twin-screw, that way you will have the right heat range

 

Thanks everyone for the advice. Now that I've got the right plugs, I'll give it a go myself this weekend and hopefully save $200 in labor fees. (Interesting side note: Amazon raised the price on these plugs from $4.40 to $10.32 shortly after I made my purchase.)

Now a question on the gap ... These plugs (NGK IFR5N-10) have a gap of 0.040".

The Jag Vehicle Specification guide indicates a gap range of 0.035 to 0.039" for my engine. However, my own Vehicle Care Handbook specifies a range of 0.040 to 0.043".

Which is correct? ... and is the delivered gap of 0.040" close enough that I should not mess with it?