The Sonata Manual calls for replacing the platinum plugs at 60,000 mile. If the car is running as well as it ever did and the MPG has not gone down how important is it to change the plugs?. In other words is this a case of "don't fix it if it ain't broken?"
I can't speak for Hyundai, but my last couple of GM cars went a minimum of
100k and the plugs were still working OK. I change my LeSabre at 118,000 and there was no change in mileage or performance. My '91 Regal went to the bone yard with the second set of plug in it and my LeSabre will do the same it seems. The wires, however, did need changing as they were starting to arc.
With the advent of catcons it is fairly important. A miss of any significance can put enough raw gas out the exhaust to overheat and damage the converter. A converter is MUCH more expensive than a set of plugs, even the expensive platinum plugs, because most catcons have a lot more platinum in them than the plugs have!
You may be thinking of iridium plugs, as platinum plugs aren't particularly expensive at ~$20 for 4. For that matter, you can replace them with NGK V-Power copper plugs, which are dirt cheap (under $10 for
4) and actually perform better than platinum or iridium plugs, they just have to be changed more often (~ every 30K miles).
Matt's correct about the risk of damage to the converter. You can wait until the plugs start to misfire, but you'll need to stop driving the car right away (have it towed) and replace the plugs before driving it again in order to guarantee you've done no significant damage to the converter(s).
I changed the iridium plugs in my 2001 3L V6 XG at just over 110,000km. I had thought the car was running just fine but could definitely feel more acceleration up these steep mountain roads where we live after the change. The old plugs all looked OK just used with no real deposit build up or badly eroded electrodes. 6 years on one set of plugs was good for me so why stretch it. BCinBC
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.