I would prefer to replace them at a convenient time for me, and not find out they're no good half way up the Brenner pass. I'd at least check the plugs around interval time.
Spark Plug Replacement Intervals - Why?
- Thread starter leeharvey418
- Start date
I would prefer to replace them at a convenient time for me, and not find out they're no good half way up the Brenner pass. I'd at least check the plugs around interval time.
Patman
Staff member
I have 176,000 miles on my Civic and it’s still got the original plugs. Engine runs smoothly and still gets over 60 MPG on a lot of my drives so I’m pretty confident that they are still doing their job perfectly. At this point they might already be difficult to remove so I might as well just keep going! I recently talked with another 2.0 Civic owner who has 250k on his plugs and they are still going strong. Honda uses NGK laser iridium plugs
Because it's preventive maintenance.
It's cheaper to replace 4 plugs at 80K-100K than to also wear your coil packs from increased load to jump the larger gap.
You might not see a drop now, but are you recreating the exact conditions? Ambient temps, warm up time, idle time, traffic, making the same green lights in traffic, etc.
Why risk it? Keep your engine operating as efficiently as possible. I replace my plugs and upstream sensor(s) at 80-100K to maintain peak efficiency.
Plugs wear out, just like tires, brakes, belts, etc.
How long do you run your engine oil in this vehicle before changing?
dnewton3
Staff member
Folks -
The discussion is fine. The taunts are not.
Be careful or the thread gets locked.
The discussion is fine. The taunts are not.
Be careful or the thread gets locked.
A pertinent fact that's missing from this thread is that Mazda calls for a spark plug change at 40,000 miles for its 2.5L turbo engine, compared to a much more reasonable 75,000 miles for the non-turbo version of the same engine. So the OP's question seems even more important since 40,000 miles seems an absurdly small interval for a spark plug change. I've been wondering this myself since I have a Mazda6 turbo with 37,000 miles.
I’ve seen some engines run well on some severely worn plugs. My only concern is when the plug can no longer be removed without damaging the threads in the cylinder head. A simple job turns into a nightmare very quickly.
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I would follow mfg's suggestions myself. Why is it 45k on the BMW N54 (seems very soon), and 120k on the Lexus 3UZ-FE? I am not sure and I just did them when I reached those mileages. 45k is soon to me but I figured engineers have a reason and it's programmed into the car on the dash as well (CBS). I did choose to go with OEM Bosch not OE BMW. And Lexus I did amazon (ouch!) aftermarket! Both cars are fine.
I get neglecting it if not DIY. I heard it can get very expensive on transverse mounted V-6's. Like $800+ from what I've heard.
I get neglecting it if not DIY. I heard it can get very expensive on transverse mounted V-6's. Like $800+ from what I've heard.
Yes, 100k over the manufacturer's recommendation.
But that is the point being made - you will get no indications that they are wearing out until they take something else (like the coils) with them.
They might be fine. I did the plugs (iridium) on the Tundra at 80,000 miles and they looked great. (Edit - the gap was greater, they had worn a bit, but the electrode ends were still sharp and the gap wasn’t too bad)
Still, I am glad I did them, because they were nearing 10 years old, and eventually, galvanic corrosion could seize them in place. Once I’ve done all the other work to get them out, I am not putting used plugs back in. Here are the Tundra plugs, old and new:
I’ve seen plugs at their recommended interval be completely worn out, too.
Here is a completely worn out set of of Iridium plugs, that was in service for less than the factory interval, shown next to a new plug.
No obvious symptoms yet.
So, which are yours?
Neither of these had your “mechanical engineer signs of failure” - but that last set was putting more stress on the coils and the car did run better with the new set in place.
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OK. How 'bout, "because the learned, wise and beneficent authors of the manual say so"?
Playful rib...not a taunt.
Why not do them if they’re easy? Riding around on old spark plugs is like trusting your fuel minder saying you have 50 miles left and you’re 30 miles from a gas station. You’re probably ok but why put yourself in that position to begin with. I subtract 20% from what my manual says. Instead of an air filter change @25k, I do it at 20. The plugs were supposed to be done @100, I did them @80. Not to mention that removing a plug only gets harder the longer it’s in there.
I wouldn't call the job "easy". There's an assembly over the middle two plugs you have to detach and move out of the way. Looks pretty easy from a youtube video to lose a screw or otherwise damage something. This is the main deterrent that makes me want to wait until 50-60k do replace them instead of the manual-prescribed 40k.
I had many misfires in my 6+ decades and have never replaced a catalytic converter for any reason other than rust. And have replaced exceedingly few coils. And never from leaving spark plugs in too long. Almost all the misfires have been caused by bad plug or wires.
I've done experiments just cleaning and regapping plugs and reusing them. The plugs "wear" out. What does that mean? For some (unknown to me) reason the insulation ie: ceramic breaks down where it meets the metal thread body and the spark starts leaking out there. You can see black carbon traces begin to appear.
Also invisible cracks occur in the ceramic other places where voltage/spark starts to leak and carbon traces appear.
Wires simply wear out and start leaking voltage too. I don't know what happens to that material.
To me, no big deal. You'll know it when it starts to miss and the computer will pick it up. But you absolutely have to get them out of there regularly to put some never-seize on the threads. Or you won't be getting them out. And that's a big deal.
Personally I just replace them now at the recommended intervals because I have learned that they are eventually going to fail and the cost is not that material in the scheme of things. And I have them out anyway. But again, no big deal.
163,000 mi on the plugs on my $500 Saturn Vue (GM 54 deg V6).
I'd change them but you have to remove the intake manifold to get access to the plugs.
Maybe someday....
I'd change them but you have to remove the intake manifold to get access to the plugs.
Maybe someday....
edyvw
$50 site donor 2025
You already got answers above.
@leeharvey418 I think this was touched on, if not....when you do change them, be sure to use the OE plugs. Many engines are very picky on plugs and the wrong ones can definitely cause issues.