How often should you replace the spark plugs

How often should you change the sparks plugs? My car manual says every 15, 0000, and I had been doing that base on the maintenance schedule. However, a friend of mine says now days spark plugs are made to last longer than 15,000 miles. The last time I had my plugs replace was at 55,000 miles. Right now I have just over 78,000 and I’m wondering if it?s time for a tune-up.

Model year?
Type of engine?

15k miles??? I haven’t heard a mileage that low on spark plugs on cars for 30 years. Not since the introduction of electronic ignition. Your manual may say INSPECT the plugs every 15k miles…but REPLACE…I don’t think so.

Really need more information. The change interval varies widely depending on Make/Model/Year.

Not only the vehicle, but also what type of plug is used. Standard copper plugs (which I recommend) last about 40k miles. Platinum plugs about 60k miles…and the new Iridium plugs over 100k miles. But the vehicle they go into also have a influence on plug life.

It’s a 2000 Hyundai Elantra with a 4-cylinder engine.

I believe the 15,000 mile spark plug replacement is listed under the “severe service” maintenance schedule.

My daughter made the same mistake with her Hyundai, and after replacing the plugs at 15K she discovered the “normal” schedule which called for new plugs every 30K miles.

Spark plugs are so cheap and easy to change on a four cylinder engine that it really couldn’t hurt to change them every 15,000 miles. However, you should inspect them to determine whether or not they need to be replaced. I am guessing yours are fine and a 30,000 mile interval should be fine.

Are you still driving around with the original spark plug wires? If so, check their condition and see if they need to be replaced. They will cost more than the plugs, but if yours are old and cracked, replace them.

Not just higher voltage ignition, but also unleaded fuel increased the life of plugs.

I was wondering about the opposite on my V10 F250. I want to change before recommended time. The factory change interval is 100,000 miles. I was going to do it early, plugs are only $3ea, but Mechanic buddy tells me the labor time is THREE HOURS! Maybe I will wait until 50,000 miles.

You can easily wait until 60K or higher. I use the Motorcraft platinums in my 2000 Ford Explorer, and they looked good at 60K. I finally changed them after 80K. Going to get a new set this spring, now that I’m at 162K. I would recommend you stick with the Motorcraft brand at the Ford dealer. A lot of other brands don’t last as long.

Any idea on the technical degree of difficulty in designing a secondary ignition wire set that will never need replacing (OK say 300,000 mile, 20 year design life) any idea on cost?

I really like coil over plug designs, I want to see secondary ignition problems go away.

Is it $3.00 for 100,000 mile plugs? this is pretty cheap. Check again on what type/quality plug you are getting for $3.00.

Good point. Probably Botched Platinums, which is why I recommended sticking to Motorcraft. Those Botched plugs run horribly in a lot of domestics, and definitely don’t last near as long.

Go with the manual recommendations.

Spark plugs have evolved from copper core to platinum and on to irridium. The real difference is in the center electrode from which the spark originates. Irridium is the hardest, some 8x harder than platimun, and those are the extended life plugs in the new cars. Material moves with the spark, some vaporizing, and the harder the material the slower the electrode erodes.

This has apparently happened in a very short time. While my 2005 is irridium, my ladyfriend’s 1995 is copper core. Without looking at your specs we’re all guess what type you have…but the folks who wrote your owner’s manual weren’t guessing. And using the severe maintenance schedule can only benefit.

There are other factors such as new cars running much cleaner than our old '60s and '70s buggys did, and there are whole lot of reasons for that, but the owner’s manual is the gospel.

Even if you have extra long life (100K miles or more) plugs, don’t leave them in that long. Either put anti-seize compound on the threads, or take them out every 30K or so to check them. You don’t want them welding themselves into your cylinder head!

I agree with the recommendation not to leave plugs in that long. 50K is a good, memory-friendly interval for those 100K recommendations.

I have to recommend that rather than anti-seize (which some plugs recommend against) a torque wrench and proper installation is preferable. A beam-type torque wrench can be bought at Sears for under $25. It’s an excellent investment.

I really wish I could get my hands on a gauge-type torque wrench. I still haven’t gotten used to the ones that are supposed to click.

Have you tried a beam-type? The ones with the pointer and scale up by the handle? I prefer them.

I use a in-oz click type for spark plugs… I do not like the feel of the standard click type torque wrenches at the lower end of the range. I would never use my 20-120ft-lb whrench for a 20 ft-lbs fastener. Gauge types are expensive, but I used them on aircraft components, as well as top quality click types “back in my day”.

I bought a few different ranges. I like the beams because I can see how much torque I’m using at each stage of the process, from initially to the final torque check.

Or perhaps I’m just old fashioned…

Anti-seize if the manual calls for it and not if not. The addition will require different torque. In applications with aluminum heads and no anti-Seize that I know of, nickel-plated threads on the plugs are called for. Do not deviate from that or you may well not be able to get the plugs out without taking the head threads with them.