Wrong spark plugs fitted?

Technical Area Routine Servicing
1

Hi all,
Just started to swap the plugs on my 2008 2.0 mk3

I have new Denso ITV20TT to go in
But the one I took out is a different length. Out came an NGK IFR6E 11.
I am pretty sure the Denso is the correct plug, but with it being longer, I am paranoid.
I also note the NGK is a crush seal where as the Denso is a taper.

Can anyone confirm the plug type and or length?
The NGK thread (from seal to electrode) is 18mm, the Denso is 23mm.

Thanks.

2

NGK ILTR5A-13G

Denso ITV16TT

Who knows? Above sold by mx5Heaven and AutoLink, vehicle specific for mk3 2.0 models.

Mx5Parts offer 3 versions but no part numbers quoted.

Some sellers quoting Denso ITV 20TT for 2.0 model?

Blooming minefield! You do right to query it. Sorry can’t be of more help to you.

Barrie

3

Hello Mate,
Strange one that.
Just done some research and all the plugs listed come out as 25mm thread length.
Seems strange the NGK ones are short (or as you say were the wrong ones).
https://www.motor-doctor.co.uk/spark-plug/mazda/mx-5/mx-5-iii-nc/18887-2-0

4

Itv20 will work and have the correct taper seat. Your ngk is more mark 1 than mark 3. I would be inclined to squirt some wd40 or other lubricant into the thread holes and carefully work one of the plugs in and out to clean any carbon from the threads not covered by the ngks

5

Thanks all.

All the cross checking I have done tells me the Denso ITV20TT is correct and the NGK was wrong.

Will wet the threads with some carb cleaner, that may soften any carbon deposits, run a tap in first and will use a torque wrench when fitting.

The unexpected joys of buying an old car!

6

I agree with that. :+1:

7

It might run a bit better without the plug shrouding though.:grin:

8

If you use a tap it may be better with grease just in case it takes a shaving and they drop in and foul the new plugs

9

Well, I declare that a success.

The low rev, low load coasting stutter I was asking about on another thread is now gone, and the seat-of-the-pants-ometer says the engine is stronger from about 3.5k revs upward. Livelier, more torque.

So increasing the compression ratio a fraction and re-optimising the combustion chamber shape was an outcome I did not expect when I stepped outside this morning. Happy days. Thanks for the input everyone.

2 Likes
10

Excellent news and one of life’s little mysteries.
Glad it’s all sorted. :+1:

11

Just as an aside, I have just had my 10 plate 1.8 roadster serviced by a local mechanic, its got 37000 on the clock, he changed the plugs, and said they were the original items and hard to get out. Funny thing is when I downloaded the service history it said they had been changed at 20000.