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Old 06-10-2014, 12:49 PM   #1 (permalink)
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timing belt & spark plugs ~ which ones?

I'm having the timing belt & water pump replaced in a week, along with valve cover gaskets, and would like recommendations of any adjustments. So far I've ordered a Gates timing belt kit, Felpro valve gasket kit, Beck Arnley 192 thermostat and gasket, and am considering which NGK plugs to get. The recommended plugs on the NKG website and prices on Ebay are as follows:

2262 ~ copper ~ 2.59
7098 ~ platinum ~ 3.24
4363 ~ platinum ~ 9.04
2477 ~ iridium ~ 6.25

My objective is mpg, and I'm tending to the 7098's but am open to any of the upgrades. The site states both the platinums are good for fuel economy but doesn't state the same for the iridiums, just saying fuel efficiency, whatever that is.

Regarding the timing belt, should I have them stick with the OE setting? I'm quite happy with how the car's been running to this point. I'm going to have them check the head gasket too, though I never need to add any coolant. I'm tending to change the distributor cap & rotor too. I'm interested in any ideas as this is quite a bit of work to be done.

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Old 06-10-2014, 01:54 PM   #2 (permalink)
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Spark plugs have next to no effect on fuel economy as long as they're working. The different types of spark plugs simply determine how long they last. Coppers go ~15k miles (all numbers are YMMV, also you can regap them to go longer). Platinums are more around 50k miles, and irridiums are good for 100k miles.

Personally, I think a lot of people have had issues with platinum plugs, so I tend to stay away from them. I get iridium if I'm going to keep the car a long time, or I go with coppers if I'm not.
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Old 06-10-2014, 01:56 PM   #3 (permalink)
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I think I am running iridiums right now, just because I needed to change them and what the hell. But I keep a pair of the OEM equivalent set aside to install before emissions. You also live in Cali, so keep that in mind. Any engine changes that affect emissions will produce an automatic fail when you get the car smogged. Ignition timing is one of the things they check. I don't know about valve timing, but if they can, I'd bet they do, just to be on the safe side.
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Old 06-10-2014, 04:47 PM   #4 (permalink)
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I replaced the iridium plugs in my Ranger at 130k miles. The gap was almost twice the recommendation when new, which is why I'm sure they were original. No difference in performance or economy.

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Old 06-10-2014, 08:41 PM   #5 (permalink)
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ngk V notch copper plugs

Thanks for the feedback. It seems to me the faster acceleration with platinum or iridium plugs would result in shorter pulses for each coast, and thereby better mileage. If not, then they must burn more gas to get the faster acceleration, which becomes a tradeoff. Why would iridium plugs increase emissions or affect valve timing? Based on the comments, I'm getting the basic ngk copper plugs, the same ones recommended in the manual.
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Old 06-10-2014, 08:55 PM   #6 (permalink)
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My sidekick requires the V grove ngks. I got the autolite xps for the insight.
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Old 06-10-2014, 10:39 PM   #7 (permalink)
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I run iridiums as well. I doubt they do much for fuel economy, but they last a looong time. They are usually cheaper simply because they can outlast 5-6 sets of copper plugs.

My old man has a spark plug cleaner from Harbor Freight, and he pulls his iridiums at 50k and 100k miles to clean and regap. He says he usually get 150k from each set of plugs. I'm lazy, and just toss mine at 90-110k and replace.
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Old 06-10-2014, 10:48 PM   #8 (permalink)
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If you pay someone to put plugs in, I'd get iridium so you can go the longest interval before having to pay a mechanic to replace them again.

However, if you're going to sell the car within the next 5 years, I'd just go copper.

You will get a CEL if one of the plugs is causing a misfire. Otherwise, the plugs won't have anything to do with MPG.

I'm not aware of any adjustment that can be done to intake/exhaust valves to get better fuel economy. My assumption is anything other than stock would get worse fuel economy. Perhaps it could be adjusted for top end power, but that would certainly hurt fuel economy.
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Old 06-10-2014, 11:31 PM   #9 (permalink)
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Different engines will respond differently to changing spark plug type. I only have experience in platinum and double platinums and I really like them. If I remember correctly, iridium has a higher resistivity than platinum, so that is something to consider.

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Old 06-11-2014, 12:22 AM   #10 (permalink)
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The MAJOR benefits of platinum and iridium are:

a) their resistance to ionic disintigration (electrons destructively stripping metal atoms during each "arc" firing), and...

b) their much higher MELTING temperatures.

...as compared to older nickel-iron and copper core plugs. Copper-core plugs actually DO have better electrical conductivity, but they also have much lower melting temperatures and greater ionic stripping (electrode erosion).

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