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Sparkplug gap question. Iridium vs Platinum

34K views 10 replies 9 participants last post by  horsehockey 
#1 ·
Hey everyone.

I changed my plugs today and I went with double platinum plugs. Rockauto, amazon etc all say gap to .40

The manual and another old thread on here say .35

The plugs that were in the engine were Iridiums.

Question is, do I go with the .35 gap in the manual or is that gap specific to iridium plugs only and should I now gap to .40 for the double Platinum?

Thanks.
 
#2 ·
eyeballeater said:
Hey everyone.

I changed my plugs today and I went with double platinum plugs. Rockauto, amazon etc all say gap to .40

The manual and another old thread on here say .35

The plugs that were in the engine were Iridiums.

Question is, do I go with the .35 gap in the manual or is that gap specific to iridium plugs only and should I now gap to .40 for the double Platinum?

Thanks.
While it is not a choice for the answer to your question - Personally, I would have gone with the Iridiums like the car came with. Do you have a reason for not doing this - i.e. Do you know more than the Engineers at GM ?

Sorry for being a smart a$$, but i am curious why you decided to change.
 
#4 ·
I replace with AC DELCO.

The plugs for your vehicle will have a new gap- if there has been changes......


for your vehicle...
2011

it shows.

Iridium Spark Plug
Part Number: 41-108
Product Notes:
Iridium Spark Plug
All; OE; Gap .040; LS, AWD*; LS, FWD*; LT, VIN: C, AWD, Eng Code: LAF*; LT, VIN: C, FWD, Eng Code: LAF*; LTZ, VIN: C, AWD, Eng Code: LAF*; LTZ, VIN: C, FWD, Eng Code: LAF*

Per Vehicle: 4; Years: 2010-2011



and for the 6 cyl.

Iridium Spark Plug
Part Number: 41-109
Product Notes:
Iridium Spark Plug
All; OE; Gap .043; LT, VIN: 5, AWD, Eng Code: LFW*; LT, VIN: 5, FWD, Eng Code: LFW*; LTZ, VIN: 5, AWD, Eng Code: LFW*; LTZ, VIN: 5, FWD, Eng Code: LFW*

Per Vehicle: 6; Years: 2011-2012
 
#11 ·
I replace with AC DELCO.

The plugs for your vehicle will have a new gap- if there has been changes......


for your vehicle...
2011

it shows.

Iridium Spark Plug
Part Number: 41-108
Product Notes:
Iridium Spark Plug
All; OE; Gap .040; LS, AWD*; LS, FWD*; LT, VIN: C, AWD, Eng Code: LAF*; LT, VIN: C, FWD, Eng Code: LAF*; LTZ, VIN: C, AWD, Eng Code: LAF*; LTZ, VIN: C, FWD, Eng Code: LAF*

Per Vehicle: 4; Years: 2010-2011



and for the 6 cyl.

Iridium Spark Plug
Part Number: 41-109
Product Notes:
Iridium Spark Plug
All; OE; Gap .043; LT, VIN: 5, AWD, Eng Code: LFW*; LT, VIN: 5, FWD, Eng Code: LFW*; LTZ, VIN: 5, AWD, Eng Code: LFW*; LTZ, VIN: 5, FWD, Eng Code: LFW*

Per Vehicle: 6; Years: 2011-2012

Just bought a new set of NGK Iridium's (P/N: LTR5IX-11) for my 2011 Terrain, 2.4L. Guess what? Pre-gapped at .040".
 
#5 ·
Rit said:
While it is not a choice for the answer to your question - Personally, I would have gone with the Iridiums like the car came with. Do you have a reason for not doing this - i.e. Do you know more than the Engineers at GM ?

Sorry for being a smart a$$, but i am curious why you decided to change.
Don't know more than GM. If I was even close I wouldn't be asking a question about gapping.

I read an article that says for DI engines they argue that platinum will outlast iridium. (6th paragraph)http://www.hstuning.com/blog/uncategorized/explaining-the-spark-plug-options-for-the-fsi-tsi-engines/

Platinum was easier to get for me in rural Manitoba.
 
#6 ·
Iridium is better. . .

It comes from meteorites and Outer Space . . . . . . :cheers:

Plus. .. it is IN the Platinum group of metals in the atomic scale:

. . ." Iridium is a chemical element with symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, iridium is generally credited with being the second densest element (after osmium) based on measured density . . .
It is also the most corrosion-resistant metal, even at temperatures as high as 2000 °C. "
 
#7 ·
Stick with the manual for the gap. The platinum plugs will wear out faster, so starting with a larger gap is only going to hasten the time before you have spark blow out.

Since these are what you got, you'll just have to roll with it. Irridums are beyond good. They are good past 100K miles. I replace a set at about 115K miles, and they were still gaped perfectly. No wear at all. I saved them because I jsut couldn't through out such nice plugs.
 
#8 ·
Iridium is better....sort of. Iridium has some properties that enhance the overall performance of the engine. The main one, in my opinion, is that the use of iridium plugs (along with other innovations) gives manufacturers "bragging rights" about reduced maintenance costs. They also can crow that they are because they producing low maintenance engines that those engines are of a higher quality.

About iridium plugs:

First, you should know a little about an iridium plug. The iridium in the plug is limited to the cathode tip. The manufacturer laser welds a tiny iridium wire onto the end of the center electrode. Other than that, the construction of the plug is pretty generic. Remember, iridium is a rare metal and today's price is $650 per troy ounce, (for comparison, platinum today was $933 per oz.) so they use as little as possible.

The biggest advantage to using iridium in a spark plug is it's ability to not wear while operating in the harsh environment of a cylinder. The longevity of iridium is one of the things that allows auto manufacturers to stretch plug changes to 100K miles, or more. Since the center electrode resists spark erosion so well, the diameter of the tip can be reduced to a fine point. A small electrode will concentrate the electrons to that spot and enable the spark to more easily be generated. By comparison, a copper plug with a squared off electrode wastes some energy because the spark can't decide where to jump from and relies on a coronal discharge to generate the spark which is "wasteful". Additionally, since the iridium resists electrical wear the plug voltage can be somewhat increased for a greater spark potential, but shorting through the plug wire insulation limits the amount of voltage that can be applied. It should be noted that conductive resistance inside the plug is not a significant player in strong spark generation since you are already dealing with resistor plug wires (to cut down on radio noise and electrical interference of other sensitive under-hood systems).

So what vehicles should have iridium plugs?

Any waste spark engine (think Dodge V-10) that has one coil servicing two plugs should have this plug. These engines fire each plug on the off stroke in addition to the compression stroke so they get double the electrical wear. Additionally, any vehicles that have difficult plugs to change are also a great candidate for these plugs. A good example is the Equinox 3.0 where the intake manifold has to be removed for access to the plug. Finally, any vehicle that has an extend plug change interval (say 100K miles, or more).

So as you can see there are some advantages to using this type plug but generally it's up to the owner. If you are like me and don't want your plugs in there for a long time ( I change mine at +- 60K miles) the advantage is pretty much negated.
 
#9 ·
What's confusing here is the owners manual for the 2011 GMC Terrain 4-cylinder calls for a spqark plug gap of .0350. However, the Spark Plug Part No. 41-108, which is what GM puts on the car originally, has a gap of .040. So, apparently the owners manual is incorrect. This threw me off where I followed the owners manual and ordered Part Number 41-988 with a gap of .035 only to discover that 41-108 is what the OEM part is. Best to replace with what GM originally installed.
 
#10 ·
I don't remember the details, but I do remember that this was discussed on this forum. I went and re-gapped my OEM installed plugs, and remember there being a difference, but it may have just been the placebo effect. You should be able to find the thread from probably 5-7 years ago.
 
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