So I have a 2000 Ford Ranger XLT 4.0L V6 OHV Engine and I recently replaced the spark plugs. The thing is, the original recommended spark plugs have a gap of 0.52-0.56, which is what is recommended in the Haynes manual. However, I think some time between 2000 and now, the recommended plugs changed to another model, which is factory gapped to 0.44.

The question I have is - which takes precedence? Should I be re-gapping these plugs to 0.54 because that is what is recommended in the shop manual, or should I be making sure the gap is 0.44 because that's what is recommended for these particular plugs?

2 Answers 2


You can find the spark plug gap specifications on a sticker that will be either on the radiator support or on the underside of the hood (there are other locations such as the strut towers, etc). This is the gap that should be used when using the OEM spark plugs and even when using an off-branded plug that is a valid replacement for the OEM brand. Here are a few examples of what the sticker will look like.

(source: autozone.com)

  • It's definitely the valid OEM replacement, but you're saying one thing and mikes is saying something different. The one the owner's manual recommends is now factory gapped to 0.44, but the shop manual and the sticker (which was put on there when the plugs came factory gapped to 0.54) recommend 0.54.
    – Paul
    Commented Jun 21, 2013 at 11:52
  • 1
    The Catalyst is what should be followed. Shop manuals & Owners manuals are good references. The sticker has all the information about your specific vehicle.
    – cinelli
    Commented Jun 21, 2013 at 13:02
  • The problem is that that sticker is 13 years old and was printed before the recommended spark plugs changed their gapping. The original spark plugs were discontinued and the successor parts are gapped smaller. I'm thinking you are right since everything I'm finding is telling me to gap these to 0.54, but I'm very concerned about why the factory gap is 0.44.
    – Paul
    Commented Jun 21, 2013 at 14:39
  • 2
    There are a number of reasons gaps can be changed. For instance as the electrode erodes the gap will get larger. Too large = poor running condition (the same applies for the gap being too tight). But this also doesn't mean go tigheter on the gap.. The tigheter the gap the hotter spark and the more beating it takes. Quality of gas / additives used in making the fuel all play an effect on it's flashpoint which play an effect on the spark plug gap. I wouldn't worry much about the gap change. If you notice a running condition then you know where to start.
    – cinelli
    Commented Jun 22, 2013 at 23:31
  • Think you're confusing the 4.0 and 3.0. Smaller uses the 44 gap while the bigger uses a 54.
    – Dan
    Commented Nov 7, 2018 at 2:29

I would verify that the new plugs are in fact the correct ones for the vehicle. If they are a different brand from those originally supplied I would cross reference the numbers just to be sure. If everything checks out, gap the plugs to the plug makers recommendation. The plug is designed with a gap setting that keeps the ground electrode perpendicular to the tip. Opening or closing the gap beyond those specifications results in a larger or smaller gap from one side of the tip to the other.

  • 1
    Problem is the same plug number can be (and is sometimes) used in 50 different vehicles with 5 different gap specs from car manufacturers, this is the problem the OP is seeing.
    – Moab
    Commented May 3, 2016 at 0:50

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