So it’s been awhile since I had to replace my plugs. The plugs that were recommended, and that I was using, were the NGK ITR6F13 (Laser Iridium). Now when I look up the recommended plugs for replacement it says these ARE NOT recommended and apparently “don’t fit”, which is odd because that’s what was recommended before and what is currently in there.

Now the recommended plugs, and apparently exact fit, are NGK TR6AP13E (Laser Platinum). So I’m confused why now the Laser Iridiums are indicated as they are not compatible. What’s the difference? Are the Laser Platinum plugs just the latest version?

The reasons I ask is I’m curious what the difference really is between the Iridium and Platinum, and whether I SHOULD NOT use the Laser Iridium again for some reason. I have 4 left over new plugs I had bought awhile back and i’m not sure if something had changed where i’m not supposed to use them anymore.

 

Mine is a Dec 2009 2.1V6

The TR6AP... are what I use, and the same plugs in both the S Type V6 beasts.

I would ask NGK, via their website for explanation.

I have used NGK for as long as I can remember, and they have always answered my queries promptly.
Not asked many times, but never had a "no reply".

 

ugotmaile, if you were using the wrong plug, the kitty would have told you. It is very picky about its plugs. i would find 2 more of the iridium plugs and go from there. It isn't a metal issue as both are for long term use (ie, more than 100K miles between plug changes). so, unless there is some structural issue (highly unlikely), I am not sure why they would say what they are. Yes, it could be that NGK has stopped making that version of the plug and now directs you over to the other. As was said, send a question to NGK and see what they say. i am interested in what they say.

 

Thanks, I’ll shoot them an email!

 

I asked the question and here's the answer........which actually leads me to another question..........

Answer from NGK -
"The difference is that TR6AP-13E (Laser Platinum) is a 10k ohm resistor plug. Jaguar may have chosen to use this plug instead of the Iridium to eliminate the electronic frequency interference. ITR6F13 (Laser Iridium) is a 5k ohm resistor. If you haven’t experienced any issues, you can continue using the ITR6F13"

So, my additional questions are:
1) For a smooth brain layman, can you enlighten me on how the ohm resistance, or I guess ohm resistor variance, matters?
2) They say that "Jaguar may have chosen to use this plug", but the car is 15yrs old (2006) and the "recommended" OEM plugs, at least 5yrs ago, were the Laser Iridium. Does Jag just 'change their mind' on what the OEM type plugs are for 10 and 15yr old cars?

 

So an additional piece of information to stick into your pondering. Remember who owned Jaguar when our X's were made versus now.

 

Ah........well, ****. Good point.

Still curious about the ohm resistance and how they play a role or factor.

 

I think there has been some small discussions from more knowledgeable members in arcane threads here about interference generated causing radio problems and the like. My thinking would be similar to what the NGK folks said. If you had no problems before, use them again.

 

OK, if you are curious why the resistor, here is the answer. The coil for a plug takes current from a 12 V source and it generates a magnetic field. Due to the low resistance, it creates a relatively large current (talking about 1 amp or so as I recall). The plug then changes circuit paths and tries to keep flowing 1 amp through the gap of a spark plug. Using ohm's law (ie, current = voltage / resistance), you can rearrange it to mean voltage = current X resistance. In this case, you have a significant resistance from the air gap and a fairly large current. This results in a very large voltage (for the X-type, around 50K volts). This causes a large EMF field to be produced (because of the voltage). This EMF field is some of the alternator noise that you hear in the radio and in general induces a voltage in the cars electrical system. This puts noise on all the electrical components and causes them to have to work harder to maintain their proper function. By adding the resistor, you are now producing 2 fields in different areas and they will tend to cancel each other at the cost of some of the spark energy. so, you want a larger resistor to reduce the EMF, but this comes at the cost of a smaller spark, resulting in less power in the engine. So, the ultimate question then comes, how much spark do you need to make the cylinder fully fire under worst case conditions. The 10K resistors may be ok for say 5000 RPM conditions, but get them up to 6000 RPM and you may loose a little bit of power up there just because of the spark plug. Where, a 5K resistor plug may be great through the whole range of RPMs that the X-Type can handle, but at the cost of some alternator noise which may or may not have a negative effect on the computers and whatnot.

 

As I said, more knowledgeable members a.k.a. Thermo the guru!

 

Well all be damn. Yep, I wonder if there is anything you don't know. This makes a lot of sense once it is spelled out. Thank you sir!

 

When I replaced my plugs I used Ford Motorcraft plugs, part # SP479 which was the same as the original plugs that came out. I got them quite cheaply from Rockauto

 

ugotmale, I do not know everything, I had to look this one up. But, I figured if I knew, others would want to know. So, I passed on the word I found. I do try to alter what I find to put it into more manageable language (gotta love engineer speak).

As a saying I once heard and now live by: A wise man knows how little in the world they know, an idiot thinks they know everything.

 

Definition of an Expert.

X................is the unknown quantity
Spert .........is a drip under pressure!