Hello,
I need to replace my 04Jag XJ8 (126,200 miles) Spark plugs and I would like to know which NGK to use.
Advance Autoparts sells the Iridiums NGK spark plugs OE for $13,$6.99 but it has two different ones the:
-NGK Laser Iridium ( IFR5N10) $13.48
-NGK Iridium IX ( BKR5EIK -11) $6.99
Both are Gap 0.040 from factory
So any advise guys ?
Thanks

 

Both are good choices, and the IFR has a platinum disk on the ground electrode for extended life. The IFR is what Jaguar recommended for 100k. I have used both.

I'm currently using Denso's IK16TT Iridium TT which I like better than both NGK's.

 

Why do you like the Denso plugs better?

 

Thank you 😎👍

 

Idle quality and low end torque.

 

IFR5N10 is OEM spec

 

The engine management is DENSO. Why not???

bob

 

Some People say I should replace them when engine is warm and other ppl say no because jaguar has aluminum cilinders head I should replace them when engine is cold , I'm confuse

 

Warm for sure. I tried removing one plug on a cold engine. Felt like I was going to snap the threads.

Some say squirt some WD40 (or similar penetrate) before removing...

I plan on putting a dab of copper anti seize on the top 3 threads...

 

I was told to use nickel based anti-seize when aluminum threads are involved.

 

Do not use anti-seize with such as OE (NGK) plugs as they have a coating already.

I found it much easier to get plugs out warm and no need to use WD40 (wrong substance anyway - clue is in the name).

 

Thanks for the information, I removed the ones by the passenger side and with the cold engine they came out fast and easy, some came out at 0.42 ( don't know why) instead 0.40 like NGK iridium spec for the XJ8 says but I have to gap them at 0.40 from factory not all of them were gap at 0.40 only two out of 8 some came at 0.45 no a good quality control in that factory from Japan and no anti seize needed since the NGK plugs has them coated in the material from factory. Now I need the driver side I'm crossing my fingers

 

I prefer around 0.038", (Jaguar specifies for AJ33 0.035"~0.039", and tested against coil current and burn time) and the higher the combustion chamber pressure the smaller the gap needs to be. When you remove a plug and you find the gap larger than originally set, generally what you are seeing is the amount of material that has burned away from the electrode.

 

I replaced the plugs on my 04 XJR when it developed a slight misfire under heavy acceleration. I was surprised to find they were the original factory installed plugs, Autolite APP 3923 Platinum. I bought the car 4 years ago (with no service history) and it started, idled and ran great, with good fuel economy and great power. The car had 207,000 km (130,000mi) when I bought it. I changed the plugs after the misfire began at 227,000km (141,000mi). The gap had opened up to 045" for those who are interested. Until the misfire the car ran great, even after the misfire began, it still started great, idled smoothly, got good mileage and accelerated smoothly under normal acceleration. The bad plug was #8 (P0308) none of the others were misfiring. I installed NGK INR5N10, still runs great and no misfire under hard acceleration. FWIW.


Stu

 

Be very gentle with iridium plugs (such as IFR5N10) especially the centre electrode. Very fragile.

 

Use the NGK type specified by Jaguar. Don't be tempted to use other than NGK. As mentioned by others, NGK's have rolled threads which is plated with a special metal to prevent shearing and seizing making the use of anti-seize compound unnecessery. If you use it, don't use a torquemeter as you may overtorque and risk breaking the plug off. Better and safer is to torque to 180-240 degrees as recommended by NGK. Take a look at the NGK Service Bulletins and other NGK-pages on the Web. You will find a code breaker too. The last number describe the gap: 11 means 1,1 mm gap. Supercharged engines need larger gap than naturally aspired engines. I have just installed NGK's in my XKR 2000MY following their instructions.

 

Jaguar 04 XJ8.
Thanks for the good information to all of you, the plugs from factory were in good shape and actually not crazy tight at all like must ppl thing it is wrong to over tight them, it was a smooth for me to get them out. I have replaced the driver side yesterday and the passenger side Friday on a cold engine, a little warm is ok too, like I drove it around the block once the first time when replacing the passenger side thinking that was going to be easier to get them out but no difference, mine were still the originals the gap was 0.42-43 which i think it's pretty good for a 126,320 miles 04 Jag with the OEM Iridium NGK, I thought it was going to be difficult but nothing difficult at all, I just followed the instructions of a forum fellow : He used a " 3/8 2 inch adaptor with a swivel head 360 degree screw ratchet..once the plug has broke free remove the ratchet then use a 3/8 inch 5 inch adaptor to unscrew with your hand .... make sure you remove the oil dipstick for the driverside also for clearance of the coil" All good 😎👍

 

Actually, Jaguar specifications for the AJ33 is exactly the same for NA and SC engine lines. The specification is 0.035~0.039 as stated before.

I have stated before and NGK's own documentation supports this, and that is as combustion chamber pressure goes up, (increased compression ratio or supercharging or turbocharging) the gap needs to be decreased, not increased.

 

You must have misunderstood the NGK's documentation.
Supercharged engines are usually designed with lower compression ratio than naturally aspired engines. The spark STARTS the combustion, the high combustion pressure comes AFTER the spark plug has done its job.
The lower pressure at the ignition moment allows for an increased gap.
If the compression ratios are equal, the gaps may be equal too.

 

I'm not meaning to sound rude, but you do not understand volumetric efficiency, or combustion pressure. The reason the supercharged engine produces roughly 100 more horsepower than NA engines is due to increased combustion pressure due to volumetric efficiency, even though the compression ratio is less in the SC engine. Basically, the more air/fuel mixture in the chamber, the higher the combustion pressure.

From NGK, "As an example, when you raise compression or add forced induction (a turbo system, nitrous or supercharger kit) you must reduce the gap (about .004" for every 50 hp you add)."

Concerning your information on the default gap, NGK tells you when the question is asked if you should change the gap of a newly purchased plug;

"A spark plug part number might fit hundreds of different engines from many different manufacturers. Although the NGK factory will set the gap to a preselected setting, this may not be the right gap for your particular engine. The incorrect plug gap for your engine can contribute to a high rate of misfires, loss of power, plug fouling, poor fuel economy and accelerated plug wear. It is always best to check the gap against the manufacturer's specifications. If adjusting the gap on fine wire or precious metal plugs such as platinum or iridium, be very careful not to apply any pressure or prying force to the fine wire center electrode or insulator as they can be damaged. The gap should be adjusted by only moving the ground electrode."

The correct gap for the AJ33 is what Jaguar specified, (0.035~0.039) not the plug's default shipped gap of 1.1mm (0.043)