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Old 03-05-2012, 04:54 AM   #1
lolol
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Default Why do 4cyl NA Subarus have 30,000 mile plug change interval?

Just changed the plugs on the EJ22 in my 91 Legacy. The old plugs had a gap of 0.08. No idea how much overdue from original interval.

Manual calls for 30,000 miles and recommends NGK V power, standard core.
Ok, that was 21 years ago, fair enough.

Out of curiosity, I look at maintenance schedule for 2009 H4 engine. Same interval.

My Ford Duratec came from factory with NGK Laser Iridium (Iridium tip with platinum ground backing) and recommended change interval of 100,000 miles, which I think is more typical of today. I'm surprised that Subaru still has 30,000 interval in models today.

If Laser Iridium IFR6E11 were used in the EJ22, could you expect 100,000 mle life from them?
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Old 03-05-2012, 12:55 PM   #2
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Yes, you could expect around 100k miles. Depends on driving conditions.

OEM's use standard nickel v-power plugs b/c they are cheap, and they don't have a goal of 100k mile replacement interval. All Ford vehicles (post 2007 at least) have a 100k mile goal for spark plug replacement, hence the use of iridium.
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Old 03-05-2012, 02:39 PM   #3
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Quote:
Originally Posted by Bacon117 View Post

OEM's use standard nickel v-power plugs b/c they are cheap, and they don't have a goal of 100k mile replacement interval.
Why would they not like other manufactures It's something expected in newer cars. There are a few exceptions like the powerful Dodge Charger, but more common daily drivers frequently have 100,000 mile plugs.

I believe Toyotas used platinum even in the 90s especially in their V6 cars with plugs that are hard to reach.

The plugs on Ford Duratec engine is very easy to change. Full access from the top. The EJ22 in Subaru is more difficult. So, 100,000 mile interval makes sense.
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Old 03-05-2012, 08:00 PM   #4
EdHilario
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Long story short: Use the plugs you want to use. Change them as often as you like.
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Old 03-05-2012, 09:27 PM   #5
CosmoTheCat
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DOHC Subarus have platinum or iridium plugs.
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Old 03-06-2012, 08:42 AM   #6
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Quote:
Originally Posted by lolol View Post
Why would they not like other manufactures It's something expected in newer cars. There are a few exceptions like the powerful Dodge Charger, but more common daily drivers frequently have 100,000 mile plugs.

I believe Toyotas used platinum even in the 90s especially in their V6 cars with plugs that are hard to reach.

The plugs on Ford Duratec engine is very easy to change. Full access from the top. The EJ22 in Subaru is more difficult. So, 100,000 mile interval makes sense.
All depends on the manufacturers goal. A lot of things go into that goal. For example, all Ford vehicles in North America have 100k replacement interval on spark plugs. However, outside of North America, it may not be 100k. Some locales use fuel additives, like Ferrocene and MMT, that kill all spark plugs in 30k or less.

But, in my experience, price is the biggest factor. An OEM can buy an iridium plug for around 2 dollars apiece, but a nickel plug for maybe $0.75 per piece. That's 1.25 a plug or $5 per vehicle if it's a 4 cylinder. Mulitply that over the hundreds of thousands of vehicles produced, and you get an idea of how big the savings is.
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