Why does my car schedule have a time interval for spark plug replacement

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I notice that my car manual said to replace spark plug every 60,000 miles or 60 months. Why would there be a time interval replacement schedule. Spark plugs are made of ceramic and metal. I don't see it going bad over time if you don't drive a lot of miles like tires. Paul
 
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May I sneak a question in? My 15 year old vehicle's plugs are original with very low miles (<50K). Would you change them to "break the rust" or leave 'em?
 
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To cover liability just in case anything weird goes on and they sue you for it. They assume you will have very short trip and may gunk up the plugs.
 
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Astro14

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Mileage wears out the electrodes...however...steel sparkplug shells screwed into aluminum heads will eventually corrode until they're impossible to remove. Ask the guys who owned 5.4 Ford Triton engines.
 
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Depending on the vehicle and spark plug, thread corrosion can take place. I replaced a set of AC Delco Iridiums after 10 years and they were somewhat corroded. They let go with a might squeal. They had 180,000 miles on them.
 
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Part of preventive maintenance, I guess. To get good gas mileage, protect the engine, and not stress the ignition system to an early failure. My 1st Gen CRV owner's manual says to change the plugs every 24 months or 24,000 miles, whichever comes first (probably for copper plugs). The NGK platinum plugs I put in them lasted 20,000 miles (10 years). 2007 Kia Sportage manual says change iridiums every 100,000 miles. I had to change 'em at 40,000 miles (8 years). In both cases, the spark plugs announced the need to replace when the engines ran rough. I have yet to change my 2012 CRV's factory iridiums as they are only at 30,000 miles and running well.
 
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Can also be that when they review various warranty settlements, customer complaints, internal engineering reviews and component manufacturing reports ( they conduct QA/QC audits too) they can discover that on average a plug lasts this long before any number of issues statistically manifest themselves and publish a recommendation just to avoid things.
 
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Originally Posted by Astro14
Mileage wears out the electrodes...however...steel sparkplug shells screwed into aluminum heads will eventually corrode until they're impossible to remove. Ask the guys who owned 5.4 Ford Triton engines.
Yup. Cost me ~$1300 to get plugs replaced on my 2004 F150 after three plugs broke off.
 

Paul_Siu

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so what can cause spark plug to failed prematurely assuming everything is working? Does short trips gunk up the plugs? What would be the sign that plugs need replacing, you start getting lower mileage and misfires? I have difficulty believing the dealer. My Mazda dealer tried to convince me that oil change at every 3 months and at 3,000 miles is absolutely necessary because driving in Chicago area is always severe. The manual indicate severe means driving on dirt roads, towing, hot weather, and taxi type stops. None of which describe my situation. Then again, even the manual is suspected. The Subaru said cvt fluid is for life. I plan to keep the car beyond the 100K cvt warranty period. Paul
 
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Originally Posted by Paul_Siu
I notice that my car manual said to replace spark plug every 60,000 miles or 60 months. Why would there be a time interval replacement schedule. Spark plugs are made of ceramic and metal. I don't see it going bad over time if you don't drive a lot of miles like tires. Paul
What is the year, make and model?
 
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Originally Posted by Paul_Siu
I notice that my car manual said to replace spark plug every 60,000 miles or 60 months. Why would there be a time interval replacement schedule. Spark plugs are made of ceramic and metal. I don't see it going bad over time if you don't drive a lot of miles like tires. Paul
If you drive in the city in stop and go traffic, it puts less miles, but you have may have equa or more time on the plugs, thus potentially firings of the spark plugs.
 
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Originally Posted by Paul_Siu
so what can cause spark plug to failed prematurely assuming everything is working? Does short trips gunk up the plugs? What would be the sign that plugs need replacing, you start getting lower mileage and misfires? I have difficulty believing the dealer. My Mazda dealer tried to convince me that oil change at every 3 months and at 3,000 miles is absolutely necessary because driving in Chicago area is always severe. The manual indicate severe means driving on dirt roads, towing, hot weather, and taxi type stops. None of which describe my situation. Then again, even the manual is suspected. The Subaru said cvt fluid is for life. I plan to keep the car beyond the 100K cvt warranty period. Paul
I don't know about Mazda but Mercedes went to a multi spark ignition system. It can basically fire the spark plugs 4-5 times per cycle instead of the one or two in a waste fire system. Supposed to be for more complete combustion and better emissions. So it's actually getting a lot more of a workout than regular plugs. And yes, they also recommend changing the plugs at 6 years or 60k and the consensus is that it's because they don't want them to rust out in there. You might also get slightly better gas mileage with new plugs.
 
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Originally Posted by Paul_Siu
so what can cause spark plug to failed prematurely assuming everything is working? Does short trips gunk up the plugs? What would be the sign that plugs need replacing, you start getting lower mileage and misfires?
Things that affect spark plugs are also quality of fuel and motor oil
 
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To me like others stated it would be so that the plugs can be removed without issues. Most engines now have aluminum heads and the spark plugs are steel threads. Dissimilar metals and corrosion can start and lock them in. The main reason when I change mine out I put a very small amount of anti-seize on the threads.
 
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If you plan on keeping the vehicle, pull the plugs and assuming they look ok and the gap is good, put some anti-seize or molykote on the threads and put them back in. Plugs today combined with clean fuels are extremely long lived.
 
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NGK claims their Trivalent plating acts like an anti-seize, so you don't have to worry about dropping the installation torque like you would if you applied anti-seize to them.
 
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Many car manufacturers still recommend a dab of anti-seize be put on new spark plugs, and the recommended torque is appropriate for its use. As an example, I recently replaced the plugs in one of my Miatas. The Mazda FSM said to use a small dab of anti-seize and torque to 11 to 17 ft-lb. The plug manufacturer, NGK, says to torque the plug to 18 to 21 ft-lb without anti-seize. Each torque recommendation is correct for the circumstances.
 
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I think it's just generic math they are using. Miles to years for many maintenance things has been a thing for a long time but just an average based on the days that was printed. Average US driver miles per year. 12,000 miles a year at 5 years but really, 60k is the more meaningful number. If you hit 35 k in 11 years, that's more of a time thing than miles so I'd look at them at 5 or 6 years. Seen posts where the 60 k plug check showed lots of life still there too so it may depend on the car and engine or certain specifics. I believe some just consider it a guideline and time to check but don't always rush out to buy plugs without looking a them.
 
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Paul_Siu

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Back in the old days when I had to change the spark plugs often, I would use a dab of anti-seize and a torque wrench just like Le_bow_ski. Going back to fouling of spark plugs, driving really short trips will foul the plugs because it doesn't get to burn off the build up on the plugs? What would it take to clear it? Driving 20 minutes monthly? Does it have to be highway miles? Paul
 
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