replacing all spark plugs?

[Kira]

The problem was bad insulation, right? Did ignition knock shatter the ceramic or was the ceramic faulty?

If a plug had bad ceramic material, is it possible that a run of these plugs can have the same defect?

If so, replacing all 4 makes some sense. Similarly, if one coil goes bad in a car with known bad coils, it might make sense to replace 'em all.

In my world a 4 cylinder engine doesn't punish you if leave the "other 3" in place-and one fails- as they're easy to get to.

 

[PandaBear]

I replaced just 1 plug in my Taurus back when only that 1 has a hairline crack in the ceramic insulation (OEM from factory). If the coil is bad not due to aging but due to the cylinder's condition (bad plug leads to bad coil) then I would just replace only that 1.

 

[dubber09]

I'd say don't bother replacing other plugs at that mileage.
Also, that engine is notorious at killing/cracking plugs, so keep your eyes and ears peeled.

 

[Supersonic]

It's probably fine, but as creatures of habit most probably change all the plugs at one time. With this being warranty work they will only change the impacted parts.

Just my $0.02

Another thing to be aware of, if you got the updated plug you might want to update the other 3.
UPDATED SPARK PLUG FOR 2.0T THETA-II

This updated spark plug has been improved with the thread shoulder lengthened to enhance protection of the insulator from combustion heat.

Here's where I found that originally, at page 7;
Kia Sportage Forum 4G 2016-2018+ Sportage SX Spark Plug R&D

 

[vavavroom]

I’d replace all of them. Around here the stores won’t even sell you just one plug anyway. To me it doesn’t make sense to only replace one I’d replace the rest.

I'd also replace all plugs but why can't you buy them individually? Do they only have them.in sets of 3, 4, and 5?

 

[MONKEYMAN]

If it were mine I would replace them all and not use OEM. They are known to have issues. I have the same model as you. I was saddened by the condition of the Yura OEM plugs.
https://bobistheoilguy.com/forums/threads/spark-plugs-at-32-715-miles-how-do-they-look.342810/

To put icing on the cake this weekend I am replacing all the coils with the new style ones that are meantioned in the TSB. I don't have time for the dealership and would rather spend 20 minutes of my own time to switch them out. Love the car, they dropped the ball with the plugs and coils.

 

[AutoMechanic]

I'd also replace all plugs but why can't you buy them individually? Do they only have them.in sets of 3, 4, and 5?

I’m not sure honestly. When they are in a box they are individually packaged. Like for a 6 cylinder you’d get a pack of four and two loose plugs in the single boxes. Maybe they don’t want an odd number? Though some cars now have 3 and 5 cylinder engines.

 

[vavavroom]

I’m not sure honestly. When they are in a box they are individually packaged. Like for a 6 cylinder you’d get a pack of four and two loose plugs in the single boxes. Maybe they don’t want an odd number? Though some cars now have 3 and 5 cylinder engines.

3 and 5-cylinder engines have been around for a very long time. I've never had a problem buying any number of spark plugs. Maybe where you are it's like with hotdogs and buns. The number count never matches between packages.