I am sure this has been asked many times yet when I search a get a lot of problems or situations with spark plugs but not the kind to use.

I have a 2003 4WD 4.0 V6. When I input the spark plug part from the manual in Amazon I get mainly an NGK 3951 (TR55) - I assume these are platinum.

In rock auto there are quite a few options including iridium, copper, platinum and double platinum.

So what is the correct part # (AGSF-34P never shows up but cross references to SP440 and others) and the "best" one? Help much appreciated

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2003 FX4 4.0 V6

The original Motorcraft plugs are best, they are double platinum SP440 does cross reference directly to AGSF-34P

I went with copper...they say it sparks best, just needs to replaced more often

It depends on how you drive and where. If you're a low risk taker and you just want to play it safe the OE plugs from Motorcraft will be best suited for you. If you're a person who takes their vehicle or driving a bit more serious than NGK would be our suggestion.

Been running them in everything and anything since the mid 80's, same with their wires, won't run anything else. BTW the difference in a NGK Plug vs a Ferrari OE plug is the additional $20 they charge for the Ferrari Monogrammed box - Same plug, same part number, Same plug physically, same performance with $20 more box.

Call a Ferrari dealer and get a part number, cross reference it.


If you're looking for an upgrade to the Motorcraft -

NGK p/n 2683 - TR55-1 0.054" gap x6 OE Equivalent
NGK p/n 7159 - TR55-1GP 0.054" gap x6
NGK p/n 7316 - TR55-1IX 0.054" gap x6


https://ngksparkplugs.com/en/part-finder


- Spark plug gaps I would leave the OE spec'd.

- If you're in a usually warmer climate, you may want to consider going down a heat range. You'll run a bit better and cooler. If you're in a 4 season climate just stick to the numbers of your choice above.

To check on a heat range specifically, Contact is here. they are EST

NGK -- 1-877-473-6767
Dial #1 (Application Support)
Dial #2 (Advanced Tech Support)
hours: 9:00am -5:00pm
Monday-Friday EDT

- Can't justify the iridium plugs for your application but the V or G will do you fine. You'll notice more at idle and at top of the speedometer end.


We specifically run G-plugs - "1 heat-range cooler", in both our '94 & '93 rigs along with the NGK wire set on those OHV 4.0L, never have an issue and we're in sometimes 112*-117* ambient desert temps here, in Las Vegas, Nevada + the 4.0L runs hot as it is, and then normal under hood temps.

360K+ miles on one 183K on the other original engine.

Hope that helps.



.

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12° North Industries
Las Vegas, Nevada 89118
Web www.12degnorth.com

Copper plugs don't spark any better and they do need to be replaced more. Don't take advice from "they" anymore.

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12° North Industries
Las Vegas, Nevada 89118
Web www.12degnorth.com

Thanks for the detailed reply! I'm picking up NGK plugs and wires based on your reply.

Good to hear, been using them for years.. No regrets

Can you grab us a couple Green Tea's on the way back too?

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12° North Industries
Las Vegas, Nevada 89118
Web www.12degnorth.com