How often do you replace your iridium spark plugs? Nippon Denso recommends 30K miles

[Mithridates]

for Iridium power plugs. From the Nippon Denso website:

Iridium use represents the most significant technological advance in automotive spark plug manufacturing, since platinum was introduced in the early eighties. As vehicle manufacturers produce increasingly complex and efficient automobiles, there is a greater need for long-life plugs that can tolerate leaner fuel mixtures and improved combustion processes. DENSO has responded to this need by developing its Iridium alloy, originally for OE applications. For example, many newer Lexus’ and Toyota models carry an ultra long-life Iridium plug variation (.7mm with platinum tipped ground) that is capable of up to 120,000 miles of service. DENSO Iridium Power plugs, with their .4mm center electrode, have been developed for performance applications. Because gradual wear will “round-off” firing points over time, the concentrated firing power and voltage requirement benefits will be reduced. For this reason, DENSO advises replacement after 30,000 miles.

It appears that not all iridium plugs are created equal.

[PhatRoyale]

Stick to recommended intervals.

I replaced my old Denso Iridiums at 30K, just as recommended.

[Jeff Lange]

Denso S/F series Iridiums (the 0.7mm OE style ones) have the long lifetime change interval.
Denso I series Iridium Power (the 0.4mm style ones) have a much shorter change interval.

What change interval you use will depend on what type of plugs you have.

Toyota recommends 120k miles for all stock iridium plugs (SK16R11 for the 1ZZ-FE). If you are using SK16R11, I don't see any need to change them early.

If you are using Denso IK16's or IK20's or similar, then change them at Denso's 30k mile recommendation.

What type of iridium plugs are you running Mithridates?

Jeff

[Mithridates]

Originally Posted by Jeff Lange

Denso S/F series Iridiums (the 0.7mm OE style ones) have the long lifetime change interval.
Denso I series Iridium Power (the 0.4mm style ones) have a much shorter change interval.

What change interval you use will depend on what type of plugs you have.

Toyota recommends 120k miles for all stock iridium plugs (SK16R11 for the 1ZZ-FE). If you are using SK16R11, I don't see any need to change them early.

If you are using Denso IK16's or IK20's or similar, then change them at Denso's 30k mile recommendation.

What type of iridium plugs are you running Mithridates?

Jeff

I think my plugs are the original plugs. I'm the third owner of the car, and at 80K miles, I'm starting to think about replacing them.

[fishexpo101]

Doesn't hurt to replace them earlier - depending on the driving conditions/maintenance of the car - 80K-90K might be the limit for the OEM plugs.

Best not to guess - just pull the plugs and read the end. On my car - 90K-100K was all I was able to get before significant wear on the plugs started to affect performance.

[Mithridates]

Originally Posted by fishexpo101

Best not to guess - just pull the plugs and read the end. On my car - 90K-100K was all I was able to get before significant wear on the plugs started to affect performance.

What performance issues did you encounter that you decided the plugs had to go?

[AlaricD]

A mechanic I go to from time to time recommends replacing spark plugs at 30K so that a) you can read them to see if there's a problem and b) so that they haven't seized by 100K (he says that even with anti-sieze compounds there's a chance they'll seize if left in for that long).

As cheap as spark plugs are and as easy it is to do, is it really worth it to wait for 100K?

[azncapcom]

How would one check if their spark plugs are worn and need replacing? im not sure when the previous owner changed them, so i would like to check for myself?

[Erotomania]

The 1ZZ's tendency to blow by oil is a key factor to look at with spark plug intervals. Say at 130K miles you find a notable amount of oil loss, with no signs of leaks, when changing the oil. At that point, its really impossible to say when the problem began, because it certainly did not start after your last scheduled oil change, it only became apparent. If an engine is burning oil, it is contaminating plugs. Built forged forced induction motors constantly go through plugs for a reason, the engines are built with a slightly oversized cylinder wall diameter to allow thermal expansion to take place with the new forged piston, thus allowing more than normal oil blow by. Me personally, I change plugs the first time a 60K, then 100K, 130K, 160K etc. Shorter and shorter intervals to monitor the condition of the motor at the onset of higher mileage and to help keep fresh plugs in as the engine begins to use them up faster.

Beyond that, in normal compression, NA motors I never use iridium plugs. I haven't noticed a difference and they're a waste of money, especially when I keep up maintenance as I do. They have a place and are useful, just not in average motor applications.

[AlaricD]

Originally Posted by azncapcom

How would one check if their spark plugs are worn and need replacing?

Here's how to read a spark plug.