How long do Iridium sparkplugs last? (150k miles so far)

[JEDI]

2005 mazda3i 2.0L AT, bought new.

have 170k miles.
change spark plugs twice.

1st time was iridium compatible because the oem from the dealer was like $10 EACH. gave like 10% worse gas milage.
after 10k miles, i bought oem's. same exact model # as the originals that i removed. still giving 10% worse gas milage. WTF?!

after 10k miles on those, i put back the originals. gas milage went back to normal.

now at 150k miles on the originals.
How long do sparkplugs last?
and what happens if i dont change them?

 

[LTC8K6]

I suspect that 10% is within your margin of error.

 

[JEDI]

I suspect that 10% is within your margin of error.

for 20k miles i had 10% less (31mpg hwy).
then when i pop the originals back in, i'm back to normal (34+ mpg hwy).

too much of a coincedence?

 

[onza]

Did you check the gaps on old / new plugs?

 

[JEDI]

Did you check the gaps on old / new plugs?

i checked the gaps of new plugs to factory spec but did not check gap of the orig sparkplugs. hm...

anyway, back to my orig question.
how long do iridiums last?
and what happens if i dont replace them ever?

 

[LTC8K6]

They bond to your cylinder head and you can't get them out? :biggrin:

 

[jaedaliu]

they eventually completely erode and you won't get a spark so there won't be any firing in your cylinder?

As long as your gap is fine and there's no build up on it, your plugs should be good to go.

 

[BlitzPuppet]

100K is when I replaced them in my Impala, and I believe that was recommended.

 

[JechtShot]

For most manufacturers, they normally recommend to change Iridium plugs at about 100k miles.

 

[Pacfanweb]

Not even sure what type plugs are in my 04 Suburban 5.3, but they are original and it is pushing 190k. Run 'em until you get a miss.

 

[phucheneh]

Random anecdote:

250k miles on vehicle. I think they were original. Plug boots were petrified and adhered so well that I had to just break the porcelain off of, IIRC, all but two of the plugs.

Gap: about .180"

...it has a misfire issue.

edit: platinum, also. I have no reason to believe iridium lasts any longer. Smaller electrode = shorter life; the more durable metal is to compensate for that. I would do either by 100k or so. Plugs are just not that expensive, people. General worst case on most modern vehicles? Six plugs at 8-10 bucks a pop.

 

[WhoBeDaPlaya]

I use E3s in my LS, but have replaced some of them waaay before their EOL due to COPs frying (no fault of the plugs, just a well known problem with the LS).

 

[LTC8K6]

I have a 16 plug swap coming up. Fortunately it's only cheap copper plugs.

 

[SparkyJJO]

100k miles for iridiums. Sure, they might be "expensive" at 6-8 bucks each, but it isn't like you replace them that often to make it hurt the wallet that much to spend $60-80 on a maintenance item that you're likely to do only once.

This thread does remind me I still have yet to replace the copper plugs in my car. They've been sitting on my bench for a couple months now :hmm:

 

[onza]

Life is 100k.

If you are in there checking the "gap" why wouldnt you just replace them lol.. to save 99.99 perhaps... I guess for me I would just replace them and worry about the MPG issue later. 3mpg is a lot yes but you already get 30+ mpg

 

[BlitzPuppet]

Plugs are just not that expensive, people. General worst case on most modern vehicles? Six plugs at 8-10 bucks a pop.

True on the parts aspect, but what about labor if you have someone else do it? FWD Cars are a BITCH to get to in terms of back plugs. My Impala was bad enough since I had to take the alternator off and squeeze blindly back there...

But my v6 Altima...they recommend that you take the upper intake manifold off. That'll be a pain in the ass.

Monetary cost or not, I'd rather replace it with something that lasts a long time when it comes to plugs.

 

[onza]

edit: platinum, also. I have no reason to believe iridium lasts any longer. Smaller electrode = shorter life; the more durable metal is to compensate for that. I would do either by 100k or so. Plugs are just not that expensive, people. General worst case on most modern vehicles? Six plugs at 8-10 bucks a pop.

Parts = cheap, Labor = expensive.

I did a plug remove / install job on my toyota highlander and it took me around 6hrs.

 

[Ferzerp]

Mine are iridium (or platinum-iridium) with a manufacturer specified service life of 35,000 miles.

It depends on your engine and driving habits.

 

[fstime]

Funny thing is, the cheapest copper spark plugs are actually the most efficient as it is a better conductor, they just need to be changed much earlier than platinum and iridium spark plugs.

 

[phucheneh]

I think that's kind of false logic. The efficiency of the conductor matters little in the conventional sense.

.030-.060" of air is not very conductive. Spark plug wires are not very conductive (thousands of ohms per foot). Not to mention the return path of the spark. No matter what material the anode/cathode are made of, the circuit is still being completed by an iron or aluminum casting and some threaded fasteners (and/or steel gaskets).

While there is obviously some complex engineering going on, it's not in pursuit of the ability to flow the most current. Which also explains the pursuit of spark plugs with smaller tips. It's not about the efficient flow of electricity; it's the ability to discharge the hottest, quickest arc. AFAIK the small tip aids in 'concentrating' the arc.

 

[Mark R]

It's not about the efficient flow of electricity; it's the ability to discharge the hottest, quickest arc. AFAIK the small tip aids in 'concentrating' the arc.

That's it. It's the strength of the electric field that strikes the arc. And the electric field strength is increased at points (same reason why lightning likes to strike pointy things, and why lightning conductors are pointed). A narrower electrode concentrates the field and lowers the ignition voltage allowing a longer gap.

The disadvantage is narrower electrodes run hotter because they can't conduct heat away, so need to be made of rare metals.

Iridium is the most corrosion resistant metal in existence. It's also has one of the highest melting points, so it can only be smelted or welded with hi-tech kit like electron beam furnaces or laser welders.