Hi all,
NGK site http://www.ngkpartfinder.co.uk/ says ILTR5A 13G but the ones I took out (which look to be original at 30K miles) are FoMoCo Japan ILTR6A 13G which, if they are NGK plugs, are a grade cooler than NGK site says to use. These plugs do look like they’ve been running cool and I wonder if the grade has been revised since my early car?
A web search doesn’t thow up much so I wonder what you guys are putting in yours?
Thanks, Rich
 Here’s how the old plugs look at 30K miles. Some evidence of spark erosion though the gap measures the same 1.3mm. The car has just had its 6th birthday so although they aren’t due til 62K5 miles I wanted to remove them rather than risk them becoming seized. They came out easy enough, cold engine and taking my time. No 1 cylinder was a little looser than I’d expect and showed some oil on the threads so may have been blowing a bit. The car’s garaged for the winter at the moment and has been started and run cold for shunting around quite a few times so the colour isn’t a lot of help but they do look cool with quite a lot of sooty deposits. New plugs went back with a smear of copper slip on the threads and nipped up 1/16 turn rather than torqued. I’m feeling it was a good thing to do regardless of mileage 
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 What does the handbook say?
   Regards Geoff Peace.
 Hi Geoff,
L3G2 18 110 refd *1 = “ex factory”
Gap 1.25 to 1.35mm
Nothing else or equivs, anyone got a later book?
 The sites I have looked at indicate ILTR5A13G. but then they would as they will obtain their data from NGK. I would be inclined to email NGK about the problem, I have found them very helpful in this respect.
      Regards Geoff Peace.
 Thanks Geoff, that may be the only way but they put their recommendation on the site so I guess that is their answer. I’ve put them in (5As) and will pull them after some miles to see how they look.
I find it strange not to find a cross ref or anything definitive about this on the web and still wonder what other owners have been fitting!
 I find this sort of thing interesting, I have seen a post on the Miata site which suggests the different numbers are down to Fomoco, Denso and NGK. No two plugs from different manufacturers are ever exactly the same, if you cross reference a few times you never get back to the starting point. Which is why catalogues usually say for guidance only. From the appearance of your plugs I would say you have taken the right action in fitting the ILTR5A13G. Interestingly the Denso recommendation on some sites is ITV20, on others ITV16. again a difference in heat range. It has been known for car manufacturers to change the heat specification in midstream when they get feedback on their plugs. Ultimately you are chasing a shadow!
   Regards Geoff Peace.
 Hi Geoff,
FoMoCo ones out of mine appear to use NGK numbers and are printed 6A. But can we be sure they’re the same as NGK branded 6A? I don’t have any to compare but if we look at the photos of the earth electrode shapes of 5A and FoMoCo 6A I posted they may not be. That could be for reasons of design change or OE specification I suppose but I’ll try and get a look at NGK 6A for interest.Â
So I’m guided by NGK for their own retail plug and have gone with 5A. Then had a look at how FoMoCo 6A have been running, which backs up using a slightly hotter running plug, and will keep in mind that FoMoCo 6A may not be same as retail NGK 6A! 
 A little more,
Just changed the plugs in our 2006 Mazda 6 2.0 today. Similar engine to the MX5 with separate coils on top of each plug, and they’re also listed by NGK as being ILTR5A 13G same as the MX5, so I was interested to see what were actually fitted. They were indeed FoMoCo ILTR5A 13G.
That car is on 48K and the original plugs were tired with the electrodes looking similar but worse to the pics posted earlier. They are running about right, still a bit cold looking, but that will be down to the short trips. I think they would have lasted to 62K5 miles but have just taken it out for 20 miles and it runs so much better now  Checked OBD before and after and nothing showing but there’s definitely a difference to be felt driving!
 Hi Rich , I also have a 2005 launch edition ,one of my winter jobs  was to check the plugs,  i will let you know what they are. only done 14,000 
 DAVE
2009 mk3 = 1.8 Engine L303 18 110 * . LF Engine L3G2 18 110 * , L3Y1 18 110 .
Regards JJ.
Hi Dave, that would be interesting thanks 
Every NGK recommendation I can find is for the 5A’s so they’re in and running great.
The old ones came out fine from our MX5 at 30K 6 years and Mazda 6 (similar engine) 48K 5 years but there are some horror stories like this poor guy 84K 3years, http://forum.miata.net/vb/archive/index.php/t-317271.html
You’ll have your own ideas but I did them cold and slowly and didn’t come up against any undue resistance that caused any panic - if I had I might have stopped and used penetrating oil. You’ll see much about whether to use anti sieze or not on the new ones. I’m well used to alloy heads from motorcycle days and the only ones I’ve seen stripped were tightened too much. I use anti sieze, just a few light dabs and not past the last thread, and tighten by angle (1/16 turn after seated) so the torque setting is not affected.
 Hi  Rich, Just got round to checking my plugs today. They are fomoco ILTR6A13G (factory fitted) lovely gray colour spot on .DAVE.
Hi All
Recently we had guy on the forum with a stuck plug that had rounded over when he tried to remove it with a 16mm plug socket . Just out of interest if one of you has some vernier callipers handy could you do an accurate measure of the AF of the hex of the NGK plugs please.
R-b
Hi Dave, Thanks for that. Mine had done a lot of town and shunting around the garage so the sootiness pic below wouldn’t be a true indicator I suppose. The ILTR5A13G’s are still in and she’s running very well indeed no hint of pinking so I’ll leave them and see how they go through the summer.
Hi RB, Yep, got one here, 15.85mm = 0.624" so 5/8" all but a thou. Just checked my 10mm plug socket against a 16mm deep type 6 point socket and there’s the same angular movement of the plug in both, both quite sloppy, so I’d say my plug socket is 16mm 12 point. You can see here there’s no way the 16mm 6 point would round the hex though if the plug was stuck
Hi Rich
Thanks for measurements. I asked because I wondered if there was a general problem of excessive clearance between 5/8" plugs and 16mm sockets. From your photos it would seem not.
Last year when I changed a set of plugs, they came out alright but some plugs were actually jambed in the socket. I’ve just checked this particular socket and it measures at 16.1mm. Which would explain it. Your sockets are obviously close to 16mm.
My socket came with a 3/8" drive set I bought last year, all the rest of the sockets appear to be very close to their nominal value except this one.
R-b
 Hi, yes I can imagine it starting to round the corners of the hex if it’s a 12 point type and a bit loose. Maybe look out for a 6 point one. Check before use for enough clearance at the top, I used one once which snapped the porcelain when the socket leant over a bit. This looks better, http://www.ebay.co.uk/itm/NEWSOME-3-8-Dr-16mm-SPARK-PLUG-SOCKET-DEEP-M10-PLUGS-/250859413762?pt=UK_Hand_Tools_Equipment&hash=item3a6862e102
Hi guys,Â
The 5 and the 6 refer to the heat rating of the plug. The 5 is a slightly hotter plug than the 6, the colder the plug the quicker it dissipates heat. Colder plugs are generally for warmer climates.
See this for NGK plug codes.
Mazda plugs will just be rebranded big name plugs, usually NGK or Denso.