Double Platinum OE Plugs?

[fredobandito]

About three weeks ago, my Ranger finally hit 95,000 miles, so I decided to go ahead and do a tune-up during my regularly scheduled oil change. I went over to Advance and bought the Autolite wire set and the Motorcraft SP-500s that were listed as the standard service plug. Installation was mostly uneventful.

Yesterday I filled up the tank after the first full run on the new plugs, and during my normal mileage calculation, I noticed that my mileage dropped almost 2mpg on the new plugs compared to my worn-out old plugs (16mpg down to 14mpg) under the same driving conditions.

I started doing some investigating, and I noticed that the Motorcraft part number on my old plugs was different than my new plugs. Interchanging to the parts store stock number came up with an SP-432, which is a double platinum plug specified in the Taurus variant of the Vulcan, whereas the SP-500 is a finewire single platinum plug. Both interchange with an Autolite 104 series plug and list the SP-413 nickel plug as the alternate service plug, and side-by-side visual comparison shows that the SP-500 has a slightly longer threaded portion than the SP-432, but not significantly so.

Thinking it was a goof in the Advance catalog (which happens periodically to supplier changes brought about by the CARQUEST buyout), I checked AutoZone, Rock Auto, and the Ford parts site. All of them list the SP-500.

I've heard of Ford superseding part numbers before, but in this age of increasingly strict emission standards, I have a hard time believing that they'd step down to a less efficient plug. I bought the truck used in 2010 with about 40k miles on it, so it wouldn't be illogical to assume that the plugs that I pulled out of it are the factory-equipped plugs. Then again, I know a guy with an '85 Grand Marquis with a 302 who feels compelled to replace plugs and wires on it every 5,000 miles.

Is it uncommon for Vulcan Rangers to be equipped with double platinum plugs?

Part numbers:
Motorcraft double platinum: AGSF32FM/SP-432
Motorcraft finewire platinum: AGSF22FM/SP-500

 

[RonD]

The double platinum are used because of the waste spark system.
There are 3 coils in the coil pack, and there are 6 spark plugs......................
So each coil fires 2 spark plugs at the same time, and the spark plugs are wired in series, so 1 plug sparks from center to tip(normal) and the other sparks from tip to center(reverse).
And because 2 spark plugs are firing when only 1 of the cylinders is actually on its Power stroke the other spark is "wasted" on the exhaust stroke of the other cylinder.
So they call this a "waste spark system"
And the wear on the spark plugs will be different, one bank will have more wear on the tip and the other bank on the center.

Outside of the spark plugs firing twice as many times as they would with a regular coil, lol, this wear is an issue with single platinum, where only the center, or only the tip, has the extra protection.

The Ford factory used platinum center on one bank and platinum tip on the other bank, saves money when you are buying thousands of spark plugs.
But as an end user it is just best to get double platinum for the extra miles they will give you.

As for the MPG, recheck the gaps and add a bit, spec gap should be .044, use .049.
I assume your old plugs were at that gap because of the miles on them when removed.
Factory spark plug gaps are the average gap decided on for general use, adding or subtracting .005 can make spark better for your use, wider gap will give better cold start and better below 3,000RPM performance, narrower gap gives better high RPM performance.
You can change the gap as much as .010, but I would look at other spark plug option/types if that big a change helps alot

 

[adsm08]

Try resetting the memory too. Sometimes throwing a monkey wrench at the system like that confuses things. Resetting the memory makes it figure things out faster.

 

[fredobandito]

Thanks for the responses, guys. I went ahead and replaced the single platinum plugs with properly gapped doubles.

When I get some MPG numbers back, I'll make sure to post my findings. It's a Ranger with a Vulcan, so I'm not expecting any miracle 25+ mpg numbers, especially in my driving conditions, but I'm aiming for mid-to-upper 16s.

 

[HTXRanger]

So what kind of results did you end up getting? I'm debating between the OEM Motorcraft SP-500 and the Autolite Double Platinum APP104 from Advanced.

 

[fredobandito]

I actually ended up changing jobs a few weeks ago, which sent my commute in the opposite direction, so I haven't been able to get my city mileage numbers recorded under the same conditions. Interstate mileage seemed to be just fine, in the 21-22 mpg range on the double platinum Motorcrafts, which is a little bit better than I was getting before the tune-up. The few runs I've been getting lately have been downright crap, with one down around 13.9mpg, but that's because of poor route planning on my part trying to get to the new job.

That tank aside, mileage on the double platinum Motorcrafts has gotten back to where it was pre-tune-up.

Since I ended up getting the same mileage either way, I'd say go ahead and get the double platinums. The Motorcraft SP-500s and SP-432s both cost $4.99 at Advance, and the Autolites were listing for $4.69 for the double plat, so I'd probably splurge the extra couple of bucks on the Motorcraft.