Spark Plug Change Intervals
Thread Starter
Melting Slicks
Joined: May 2018
Posts: 2,090
Likes: 599
From: Question Government
Spark Plug Change Intervals
Since I can't easily access all 8 of my spark plugs (some are quite hard to access), how often should one replace the plugs if the engine seems to be running well and there's no visual inspection done on them?
Le Mans Master
Joined: Aug 2017
Posts: 6,935
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From: New Jersey
I do mine every 3 years or so. You can leave them in there way longer if platinum or iridium. I don't see much benefit stock so I run coppers. IIRC it was something like 30k miles or 3 years on the early cars?
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
Lots of opinions on this. I personally replace the plugs around 60,000 miles.
They say you can go 100K but I think that’s too much. If you push 60K a bit I don’t think that’s a problem.
However, now that I am no driving the car to work anymore, I might consider a lower mileage.
Don't think there is one right answer.
Aside from the runability of the car, I think the plug deteriorates at 100K and pieces may break apart and gaps may open.
They say you can go 100K but I think that’s too much. If you push 60K a bit I don’t think that’s a problem.
However, now that I am no driving the car to work anymore, I might consider a lower mileage.
Don't think there is one right answer.
Aside from the runability of the car, I think the plug deteriorates at 100K and pieces may break apart and gaps may open.
Last edited by pcolt94; Apr 14, 2019 at 10:48 PM.
Thread Starter
Melting Slicks
Joined: May 2018
Posts: 2,090
Likes: 599
From: Question Government
Thanks for all your info on this. I'll go to my respected and trusted mechanic and have mine changed out soon. I wish I new when the previous owner had it done, if at all.
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
I would pull and inspect 2-3 of the plugs that are easy to reach and they will represent the condition of the rest of the plugs. If you aren't sure if they have ever been changed, I definitely would break them all free to be sure they are not seized... and if you go this far and have a socket on them anyway, just replace them with new platinum or iridium plugs. At this age maybe new wires too.
If the engine is stock, in good condition and you drive it normally, you can easily go 60-80k on a set of iridium or platinum plugs.
If the engine is stock, in good condition and you drive it normally, you can easily go 60-80k on a set of iridium or platinum plugs.
Team Owner
Joined: Jul 2004
Posts: 28,372
Likes: 3,259
From: Hartford WI
You could. That is a 5 to 10 year deal before you have to do it again, I don't have faith in that for 2 reasons. I have had larger than stock gaps out of plugs that were supposed to last 100K and IIRC, got better mileage with new stock plugs. Also, it might not be as fun to pull the head if the plug sits in it too long. BTDT and didn't enjoy pulling the head for machine work when the plug couldn't come out without drilling or whatever it is they do. It's cool if you get away with it but the one time you don't, well....
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Team Owner
Joined: Jul 2004
Posts: 28,372
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From: Hartford WI
Sure but in my case, it was, IIRC way more than slightly. 50% more than spec gap on this truck. It ran "just fine", depending on your definition, for a 70K vehicle. Changed the plugs and picked up a few mpg on the highway runs (I usually make over 50 mile runs each way). Same motorcraft plugs, same everything.
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
Yah some members of another forum (tacomaworld) say they have run the same set of plugs 250,000 miles or longer. When they finally pull the plugs and see the ground electrode whittled down to a wisp, they always say they wish they had changed the plugs sooner! I understand that excessive plug gaps can strain the ignition coil(s) and lead to premature failure.
Pro
Joined: Sep 2018
Posts: 671
Likes: 171
From: Birmingham, Alabama
Yes, they are a huge PITA to change. It took my wife and I longer to replace the back passenger plug as it did all the others combined. I agree with most, 2-3 years is cheap insurance for what the plugs cost.
Team Owner
Joined: Jul 2004
Posts: 28,372
Likes: 3,259
From: Hartford WI
Yah some members of another forum (tacomaworld) say they have run the same set of plugs 250,000 miles or longer. When they finally pull the plugs and see the ground electrode whittled down to a wisp, they always say they wish they had changed the plugs sooner! I understand that excessive plug gaps can strain the ignition coil(s) and lead to premature failure.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
I'm not as particular now that I no longer drag race my Vette. Back then it was every year.
If you have Al heads don't forget to use some Li grease on the spark plug threads to prevent seizing.
If you have Al heads don't forget to use some Li grease on the spark plug threads to prevent seizing.
Le Mans Master
Joined: Aug 2017
Posts: 6,935
Likes: 1,487
From: New Jersey
I would pull and inspect 2-3 of the plugs that are easy to reach and they will represent the condition of the rest of the plugs. If you aren't sure if they have ever been changed, I definitely would break them all free to be sure they are not seized... and if you go this far and have a socket on them anyway, just replace them with new platinum or iridium plugs. At this age maybe new wires too.
If the engine is stock, in good condition and you drive it normally, you can easily go 60-80k on a set of iridium or platinum plugs.
If the engine is stock, in good condition and you drive it normally, you can easily go 60-80k on a set of iridium or platinum plugs.
Team Owner
Joined: Jul 2004
Posts: 28,372
Likes: 3,259
From: Hartford WI
Le Mans Master
Joined: Aug 2017
Posts: 6,935
Likes: 1,487
From: New Jersey
Pretty much, nothing surprises me. It's usually a gmt800 with a 5.3l, the plug angle makes #8 a bitch. Ours had the factory 03 plug in there when I did it last year. All 7 others were replaced.
Team Owner
Joined: Jul 2004
Posts: 28,372
Likes: 3,259
From: Hartford WI
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
Caveat emptor... Another person may be very happy to sell you their world of problems. So, it is SMART to be very detail-oriented when buying any used item.