?best spark plug gap for long life iridium plugs

[scoobie]

my dodge dakota 2008 has a 3.7l v6. - owner's manual calls for .043 spark plug gap. I bought autolite xp 5224, with iridium centre and platinum ground.
I gapped them for .040 because with wear the gap will gradually get bigger and reach .043 naturally. I read the following internet picture:
http://us.st12.yimg.com/us.st.yimg.com/I/machv_2040_157904138 which shows that
an iridium plug will ignite a leaner mixture than regular or platinum plugs, and has a nicer flame kernel, so probably the minimally smaller gap that I set on this iridium/platinum plug is ?good, or ?bad.
Also, I notice the 4.7 v8 engine in the Dakota has a gap of .040, so does that mean that .040 should work well with the 3.7 v6?. I am being extremely careful to make sure the plugs are gapped EXACTLY the same, because I read a long time ago, that the precise gap is NOT as important and the UNIFORMITY of the gap, because a slightly tighter gap will fire quicker than a larger gap, the engine will not run as smooth if the gaps are different among the plugs, and possibly you could even get knocking in one cylinder with the tighter gap and not another. Also I read to put a bit of anti-seize on the threads, and use a torque wrench!

the plugs are difficult to change, so i just want to do this once, and then not worry for 100,000 miles. Can I trust my local mechanic to do this job? or should I ask the stealership?

 

[Quest]

2 things you have to observe here:

(a) iridium is a very hard-wearing metal, and somewhat less so with platinum. Both still fairs much, much better than nickel alloys that most copper-core plugs possess as far as resistance to gas erosion's concerned so no need to worry about the consequential wear on them (by then when it becomes very obvious performance-wise, it's due for a change due to mileage/service life covered anyways

(b) because platinum is so hard-wearing, the erosion to 0.043" would take a long, long time and by then when that happens, the sharp electrode firing edge on the iridium tip would have been so worn out that it's due for a change anyways

(c) with transistorised ignition, I would go as wide of a gap as the engine/manufacturer spec permits, so long as it doesn't cause misfiring. used to be gaps were set to much, much smaller than 0.043 (commonly somewhere between 0.020~0.035") was due to the rather primitive contact-point style of HV generation scheme, and they are very sensitive gap erosion and such. Not so much these days.

I never use any anti-seize (copa-slip, high temp antiseize, etc.) on all the vehicles I've serviced so far so long as you (a)observe proper plug torque spec provided by the manufacturer; and (b) remove them every 2 to 3 years so as to break free of all the deposit built up on the thread that is closest to the combustion chamber/electrode where they tend to build up there anyways.

Q.

 

[peterdaniel]

I agree... on my companies Honda Element, it has 85K miles on the original Iridium plugs.. I pulled them to simply look out of curiosity and they had perfect gap. They are not required to be replaced until 110K miles!! and I now believe them!

 

[scoobie]

thanks! i'm re gapping to .045 this should give a strong spark/

 

[dwendt44]

IIRC, the 3.7 V-6 is the 4.7 V-8 with two cylinders lopped off.
The internals are the same.

 

[Rabbler]

Spark plugs on a 3.7 or 4.7 are not hard to change. Do it yourself.
I would add anti-sieze to the threads and gap at mfg spec.

These are one of the few engines I would recommend a premium plug.
They have high current coils that wear conventional plugs quickly.
Yes a 3.7 is essentially a 4.7 with 2 cylinders lopped off and a balance shaft added to take out some of the shake.

 

[hate2work]

Gap them at spec and call it a day. Too wide a gap causes the coil to work harder to jump it. It could also effect the combustion bloom in a negative way.

 

[punisher]

Originally Posted By: hate2work

Gap them at spec and call it a day.


Wisest post in this thread.

 

[demarpaint]

I'd gap them to what they're supposed to be, they've taken all the variables into consideration when they arrived at the .043 gap. My question is why change plugs on a new vehicle? The factory installed plugs should last at least 36,000 miles on a 3.7L engine, I'd worry about them then. JMO

 

[mechtech2]

Most of the wear will be from you checking the gap to check for wear.

I am not sure of the validity or the point of that graph. If anything, it shows that any type of plug with about .040" gap is suitable.

 

[PandaBear]

Is there a way to sharpen the rounded tip again to increase the spark plug life?

 

[Cruncher]

Per NGK, irridium plugs are not to be gapped, period. The gap is preset from the factory & the gap is different than platinum or other plugs. Irridium plugs have such a fine wire that when someone trys to gap them, the fine wire will become out of align or bent. Google NGK (the company, not the retailer that uses NGK's name as its web site), ask them and they will confirm that you should never gap an irridium plug.

 

[sprintman]

You don't gap Iridium plugs period!

 

[dkcase]

Originally Posted By: scoobie


.....the plugs are difficult to change, ....

It's interesting thta you say this about your Dakota, because on a 3.7 L Jeep Liberty , the plugs are a piece of cake.

The only somewhat difficult one is the right rear, because of the coolant overflow bottle. I loosen it and pull it out of the way, but many people say they don't bother -- just use some more u-joints.

 

[mechtech2]

Of course you gap plugs. Yes - I know they often are OK from the box.
But who would not check them? Is this what you want your mechanic to do? Just throw them in?
Only common sense moderate care is needed.
Set them to the wide end of the factory range. the same as a 1955 spark plug, only use the side electrode.

 

[panthermike]

I contacted NGK about the Iridium's for my 4.6DOHC and they said the gap is .055, while my car calls for .054. The guy said they can be gapped but you have to be careful.

 

[tom slick]

.001 won't make any difference.

 

[panthermike]

Originally Posted By: tom slick
.001 won't make any difference.


Oh sorry, I didn't clarify. The point of the post is that you can gap iridiums but with extreme care.

 

[sprintman]

They are so east to damage and you are worrying about a thou? Madness!

 

[panthermike]

Originally Posted By: sprintman
They are so east to damage and you are worrying about a thou? Madness!


Let me clarify again, if I buy the Iridiums I will not gap them! My point is they CAN be gapped if necessary.