spark plugs

Probably the ones already in there. What is the recommended change interval? Most plugs last 100k today.

NGK V-Power plugs work well and are inexpensive (under $2 each). They'll last 15-30K miles and are the most cost-effective plugs. I installed a set at 45K miles and the car runs great with them.

Platinum plugs (that's what came in our cars) are more expensive, but last 30-60K miles. Iridium plugs last the longest - up to 100K miles) - but the price is outrageous and they offer no other advantages.

Depends on how you define "cost effective". As for cost per mile of the equipment, yes. As for the labor involved on some cars, you want the longest lasting plugs available. Many 4 cylinders are a piece of cake to change. Some of hte 6 and 8 cylinder require a lot of contortions, loosening motor mounts etc, to access them. You certainly don't want to have to go through that every 15,000 miles.

On my LeSabre, I'd have gone through at least 4 sets of the NGK you recommend. I just took out the originals at 120,000 and five years and replaced plugs and wires and I'm now set for the rest of the life of that car. My Regal had one plug change in 16 years. For me, that is cost effective.

Use a good name brand platinum plug that meets the heat range specifications. I recommend either NGK or Denso. There's no reason to pay dealer prices for the plugs. The same plugs will be available elsewhere at a significantly lower price.

Speaking of changing plugs, I have an '03 Elantra and have changed the plugs every 15K due to starting problems. At 13K on the original plugs the car became very hard to start, the Hyundai dealer could not find the problem and recommended a 'head cleaning'?? which was not covered under warranty, I then replaced the plugs and it gradually started starting better and after about a week it was like new. I now have 53K on the car and I am on my 4th set of plugs due to this starting problem which is fixed by replacing the plugs. Not happy about this but at least the plugs are very easy to replace.

I think that something else is going on here. This isn't a spark plug problem. Spark plugs don't get better after you install them so if the starting "gradually got better" then it wasn't the plugs that did it. A new spark plug is as good as it gets and they don't get better with age.

And a modern car engine will run way longer than 15K on a set of plugs, even the cheapest plugs.

Do you do a lot of short trips? 53K isn't much in 4 years, but it sounds like you drive the car fairly often. If that is the case, then I suspect you have a faulty sensor or something going on here. It isn't just the spark plugs, I'm 90% sure of that.

Maybe hyundaitech has an idea here.

Matt

I'd need to know more about the starting problem to offer much of a solution. I.e., does it crank not start; does it crank too long before starting; does it run poorly when started?

That's all true, but we're talking about an Elantra, which is as easy to change plugs on as any car I've ever owned. Frankly, it would be silly to pay someone to change the plugs on one, as it's a simple, basic DIY job that takes all of fifteen minutes.