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mill540 2/19/2021

2013 Honda Civic LX 4 Cyl 1.80L


Spark Plug Gap Question

I bought a 2013 civic 1.8l with 76,000 miles. I decided to change the plugs and bought the Denso Iridium 5356 plugs that are gapped at .035. Everything I read says the plugs for the 1.8l should be between .039 and .044. Looks like it had the original NGKs gapped at .044. I've installed the Denso's at the preset .035 and everything is running smoothly. Rural SC driving is getting me around 34 mpg. Should I be concerned? Should I change the gap or leave it as is?

1 Answer


Jimm 2/19/2021

Various manufacturers will have different spark plug gaps, based on these: plug heat rating, design, construction, materials, desired performance, center electrode and coating type, and defined product life. Wider gaps are often required for leaner air/fuel mixtures, but if the gap is too wide it increases the risk of misfire when the engine is under load.

The copper, platinum, iridium, and ruthenium spark plugs will each have pros/cons:

Copper center electrode = the most common and cheapest plug available. Runs cooler and provides more power in performance driving situations. Normal service life is around 20k miles.

Platinum = much harder metal than nickel alloy and has a higher melting point. Since platinum is harder, it holds its sharp edge much longer than a conventional spark plug, up to 100,000 miles. Longevity is a key advantage of platinum spark plugs.

Another advantage of platinum spark plugs is that they run a little hotter, which burns deposits off the spark plug better and helps prevent fouling. Platinum also handles high heat, enabling the spark plug to wear better.

Iridium = said to be six times harder and eight times stronger than platinum with a 700° higher melting point. Iridium spark plugs have extremely fine electrodes while retaining excellent wear characteristics. Thanks to its strength, iridium spark plugs can last up to 25% longer than comparable platinum spark plugs.

Iridium spark plugs feature a fine wire center electrode that is designed to conduct electrical energy better and increase firing efficiency.

There is a price for this precious metal. Iridium spark plugs are typically the most expensive,

Ruthenium = melts at 4233 degrees F (2334 degrees C), which is actually slightly lower than that of iridium. Testing has shown that ruthenium alloy electrodes are capable of providing up to 2X the service life of iridium spark plugs, and 4X the service life of standard nickel electrode spark plugs.
Coating acts to minimize thread galling (due to corrosion and dissimilar materials in the cylinder head) when the plugs are removed.

The gap nominal (target) setting is correct .035" for the specific Denso spark plugs you installed.

Denso #5356 Iridium
Gap .035"

NGK #93175 Iridium
Gap .044"

AUTOLITE #XP5702 Iridium
Gap .040" (1.0 mm)

SKP #SP1032 Iridium
Gap .044"

NGK 96358 {#LKR7AHXS} Ruthenium HX
Gap .044"


mill540 2/20/2021

Thank you for the information. So I don't regap this particular plug, but is it ok to use in an engine that has a .039-.044 gap specification?

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