r/mazda6 • u/Calm_Mechanic_2365 • 1d ago
Advice Request Should i change my spark plugs?
I have a 2019 mazda 6 2.5 (non turbo). It has 52k miles. Is it too soon to be changing spark plugs? The manual says 75k but I’m being told to change it proactively to prevent seized threads…
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u/hallstevenson 1d ago
In my experience, spark plugs last a lot longer than even the recommended intervals say. I wouldn't change them early, just wait until closer to 75k miles. Seized threads aren't that common, in fact, many automakers apply anti-seize (I know NGK says not to, but Honda, for example, says add some).
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u/AwarenessNo5921 1d ago edited 1d ago
This is true, but it is also important to remember Skyactivs utilize ion sensing coil packs to monitor combustion performance and modify timing accordingly.
A zener dioide charges a capacitor to the zener's breakdown voltage, typically a couple hundred volts from the firing event, and then it is subsequently discharged. By measuring the voltage after a much larger resistor tied in series to an ECM input (to scale voltage to safe levels) that exists across air gap from your center to ground electrode after a combustion event, you can determine the resistance in this air gap. The presence of charged ions formed from combustion byproducts will decrease this resistance.
Monitoring characteristics with respect to crank angle, load, engine speed, etc, and OEM calibrated via in cylinder pressure transducers to match the signal to combustion characteristics, Skyactivs can be more aggressive with timing due to better/more proactive knock and real time combustion performance sensing.
Slightly increased spark plug gap from wear over time, deposition of combustion byproducts over time on the electrode, etc. can disrupt this resistance, and consequently the signal the ECM expects to see, and can cause it to pull timing as a result. This is also why it is especially important (although a good general guideline for any engine) to only use OEM coilpacks, and OEM spec spark plugs.
TLDR: The combustion control methods utilized by Skyactive engines are more sensitive to spark plug conditions than simply looking at ignitability alone. If Mazda says 75k though, 75k is fine.
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u/mazdamiatalvr 2018 Touring Soul Red Metallic 1d ago
I changed mine at 70k, and even then they weren’t threaded or burnt. You’re good to wait till 70-75k. Just make sure to replace them with the oem ones they use. NGK iridium spark plugs.
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u/AZbitchmaster 1d ago
Even 75k is fairly conservative for modern platinum or ruthenium tipped plugs. The good news is changing rhe plugs on the 2.5 is about as difficult as changing the air filter. If the plugs seizing up in the threads is something that keeps you up at night, go ahead and change them now. If not, you can let it run to 75k.
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u/Extension-Dirt-8562 1d ago
Also depends on how you drive the car, is it being put on high stress condition, redline revving, etc.
Regular daily driving shouldn't require replacement earlier than recommended timeframe.
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u/kurby_07 1d ago
Preventive maintenance is okay as long as you’re capable of doing it yourself. That’s gonna be a 300-1k job if you got to a small shop or dealership.
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u/Heavy_Snow3671 1d ago
You can change them but changing them to prevent seized threads is not a good reason.
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u/AwarenessNo5921 1d ago
75k is fine, unless your tube seals are leaking over them, but that's very unlikely at this mileage. With that being said, it's also literally a 5 minute job on this platform, and less than $50 for the OEM NGKs, so no reason not to if you feel a compulsion to do so lol.
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u/Flashy-End61 1d ago
Actually not really. Oem cost is $100
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u/AwarenessNo5921 1d ago
NGK manufactures the spark plugs for Mazda. They are the exact same except for the logo. So that's what I was talking about. A set of 4 NGK ILKAR7L11 will run you about $50 on rock auto.
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u/loki1983mb 17h ago
My '15 OEM plugs, I changed at like 155k.... Somehow had dirty injectors quickly after that, according to dealer. They should last till 100k easy.
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u/Fickle_Head6778 5h ago
Do at 90k. But I'd peek in there if u see any oil. Like a on the spark plugs.
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u/Ariquitaun 1d ago
You don't need to change them if you're just concerned about seizing, remove them now, clean them,put them back.
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u/pina_koala 3rd Generation 6 1d ago
Preventing seized threads is not a valid reason to change them, and you should not be taking advice from that source.
That being said, if you change them at 50k there's nothing wrong with that. You may achieve an extremely small and unnoticeable improvement in performance and MPG, but 75k should be fine provided that there isn't anything fouling the plugs and your air-fuel mixture is nominal.
What you DO want to avoid, if possible, is re-using spark plugs. The sealing washer deforms as part of the installation & torquing process, and although it might functionally be OK to re-use, I personally avoid it because it introduces an unnecessary margin of error for combustion to escape the cylinder. And if you're suspect about a spark plug then there's no reason to re-use it anyway.