Will .004 difference in spark plug gap matter?

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I have a 2003 Mercedes clk500. According to ngk my spark plugs should be gapped at .040. I just bought some of their iridium ix plugs but they are pre gapped at .044. Should I adjust them or leave it as is? Will .044 give me better gas mileage? Thanks in advance.
 
Eventually, the plug gap will open 0.004" due to erosion anyway, so I would leave them as is.

I doubt gas mileage differentials could be detected.
 
It is the thickness of a sheet of paper.

Resistance is slightly more but risking breaking an Iridium plug isn't worth the chance for nothing.

Plug gaps don't open up on an Iridium plug like on a copper plug, they would probably be the same gap after 80,000 miles anyway.

Use as is with absolute confidence.
 
The spark jumping a little wider gap than usual will cause the coil(s) to work a little harder. If the coil(s) are not prone to failure in this make and model, you should be fine; however, if the coil(s) are weak or known to be problematic in your vehicle, I would re-gap the spark plugs.
 
4 thou won't matter in any measurable way. Its within the error bars of measuring the gap with a feeler tool anyway.
 
Iridium plugs are not meant to be re-gaped. There factory gap is good to go. Denso specifie not to try to re-gap Iridium plugs, since the chance of damaging the very fine elektrode is very big.
 
The .040 is a service spec meant to be on the narrow end of workable, and to have them open up over time anyway.

Since the iridiums open less, it's cool that they start more open. Leave 'em.
 
Originally Posted By: PhuongFU
I have a 2003 Mercedes clk500. According to ngk my spark plugs should be gapped at .040. I just bought some of their iridium ix plugs but they are pre gapped at .044. Should I adjust them or leave it as is? Will .044 give me better gas mileage? Thanks in advance.

Originally Posted By: MolaKule
Eventually, the plug gap will open 0.004" due to erosion anyway, so I would leave them as is.

I doubt gas mileage differentials could be detected.

Spec is 0.040" and pre-gapped at 0.044", the gap will be wider from pre-gapped of 0.044" due to erosion so that it will be much wider than spec of 0.040".

If spec is 0.044" and plug came pre-gapped at 0.040" then it will be around spec after some use.
 
Thanks for the advice guys. This is an excellent forum. You guys are more helpful and informing than the Mercedes forums.
 
I guess I'll leave them as is. After 30,000 or so miles I'll pull them out and re gap them, since it will widen a little, and if I mess up I'll just buy another set.
 
Originally Posted By: PhuongFU
I guess I'll leave them as is. After 30,000 or so miles I'll pull them out and re gap them, since it will widen a little, and if I mess up I'll just buy another set.

Iridium should be fine for 100,000 miles unless all you do is idle. Leave them.
 
Just for your info -- you'll have a little more accurate measurement with a feeler gauge as opposed to a wire type gauge. A wire gauge has a tendency to gap the electrode too narrow.
 
Is NGK OE for that model? I suspect not. Is it listed either in the owners manual or inside the hood decal? I suspect not. If you do not want to take any chances, stick with what is listed by the automobile manufacturer even that happens to be the Bosch :)
 
At the dealership those plugs are coming out of the box and going directly into the engine. There's not a ghost of a chance that the mechanic will do anything more than look at the plug before it goes in.
 
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