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Ngk Iridium Spark Plug Question

By 5th Beatle August 15, 2014

Hi all,

Had my original plugs replaced at 110K at independent shop. Now 220K on my 2005 CE. Want to try DIY this time. Manual calls for NGK iFR5-A11 iridium tip. Local parts stores have NGK iFR5T11. is this the same plug? Also, what sockets needed to remove engine cover and what readings on a multimeter should I get if the coils are normal. Thanks for everyone's help.

Yup - same plug, so called laser iridium OE plug. NGK also makes a BKR5EIX-11 Iridium IX plug - that will also work, but has a much finer center electrode. IX plug will be a couple bucks cheaper per plug, but was designed for a much shorter service life - 60K mile or less. NGK IFR5T11 has a wider electrode, like the OEM NGK IFR5A11 plug - so it could run up to 120K miles.

10mm socket will take the engine plastic shield off. I believe some of those "bolts" are clips, so you'll need some needlenose / screwdriver to try and back those off. Coils - don't need to measure them unless you think there is an issue with the coil. Resistance can vary quite a bit, from coil to coil - so it can be a little deceiving. Factory Service Manual spec's just a spark check - replace coil if they fail.

Best thing to do is remove the plugs and note what cylinder they came out of and how they look, ie. "read" the plug ends. That is far more telling them people give them credit.

Looking at my cover, I see (2) 10mm bolts and (2) plastic ones. Well, one plastic bolt is missing. Can plastic bolt be removed without breaking? Was reading NGK's website and apparently they already coat plugs at the factory, so no need to lube them again. Also pre-gapped but I've read it is a good practice to check them prior to install. Thanks for the info.

Yup, most iridium plugs come pregapped from the manufacturer, hence the little cardboard caps they put on the ends. Still, doesn't hurt to double check, just make sure you don't rock the feeler gauge and try and jam the next larger one in, pretty easy to chip iridium, since it is so hard.

As you mentioned, NGK puts a dry film lubricant on the threads - anti-seize is not required to be put on the threads. Most DIYers tend to go a little overboard with lube anyways, so they are trying to help out. Too much lube can actually cause problems, squeeze past the threads and cause a potential hot spot.

As for the plastic bolts - those are tough to pop off without breaking. I broke off mine after the second or third time I removed the cover. Some owners end up replacing those plastic clips with conventional threaded bolts or use a stud and acorn nut / wing nut. A pretty lightweight piece, if you had to - you could just use the two bolts on the front to hold the whole thing down in a pinch.

Quick tip: look down the plug well after removing the coil on plug igniter - just to make sure there is no pooled oil or other debris in there. If there is, you can dry it up with some paper towels or blow it out of there with an air compressor and blow-off tool.


Is there any advantage to the iridium plugs that would justify buying them at over four times the price of normal ones. The catalogue list 3 types of Denso plug 1 copper and 2 iridium types for Ive only had my car 3 months and was going to change them but wanted to ask if its a known thing to do thats worth the extra expense, or not.



1.6 vvti 3zzfe corolla gls.

The expensive plugs are they just for longer service life. As far as I could tell - I couldn't perceive any performance gains or losses between a plain copper, plain platinum, or iridium plug - aside from useable service life. Copper plugs - I usually get about 10K-15K mile out of them before i notice significant degradation, Platinum plugs - about 30K-60K miles. Iridium - about 90K-120K miles.

Multiple pronged plugs are hit or miss - OEM Denso dual electrode copper plug lasts almost as long as a platinum plug (two potential ground electrode, wears roughly twice as slowly). Something like those Bosch +4 plugs - hit or miss. Some have reported engine damage when one of the prongs actually fell off into the cylinder.

Some cases, it might be advisable to run a shorter service life plugs - especially if your car is consuming lots of oil, or working a a project car that required lots of changes to the air/fuel/timing map. But since most owners want to just drive the car and not worry about servicing them in short time - the industry has pushed toward longer service life components. If you don't drive as much or really like to work on the car - maybe a cheaper plug is the way to go, But if you just want to put in a fresh set of plugs and not worry about them for several years - iridium might be the way to go.


I know you have used both but what iridium spark plugs do you like better Denso or NGK.

Also what lube does Denso put on their plug. I know you said NGK puts a dry lube on theirs.

Thanks Frank.

About the same - Denso were the original ones on the car when we bought them - switched to NGK when it was time to replace them - couldn't tell any difference. Lifespan is pretty close with their OE plugs, both have a performance oriented fine wire variant that are much cheaper, but also have a much shorter lifespan.

Don't read too much into if the plug threads are coated or not. Metallurgy in modern engines is much better than before - I have yet to see plugs strip the threads out of the head unless the plugs were originally improperly installed. Even in cases of extreme service intervals - biggest issue you have to deal with is the carbon buildup on the bottom couple of threads.

As far as I know, Denso doesn't put any lubricant on their threads, but they are nickel plated? Nickel can be used as a anti-seize coating. That dry film on the NGK plug is a very thin coating of zinc chromate, acts as a natural anti-seize and rust preventative. Both Denso and NGK recommends NOT to use any anti-seize on the plugs.

Generally speaking, that is the safer way to go - not using any anti-seize. All torque values are generally reported for dry, unlubricated threads unless they indicate other wise. It is way too easy to use too MUCH anti-seize - this becomes a big issue as that extra goop that gets squeezed past the threads will become a hot spot in that cylinder - leading to misfires and excessive carbon buildup.

I just wanna say thta I like your post and I got interested in.

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