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Old 08-03-2014, 10:21 AM   #101
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Ok Mr Mechanic

My 2007 Dodge 5.7L calls for copper plugs and they need to be changed every 30k miles. The 6.1L specifies irc platinum, with 100k change interval. Some have suggested that platinum didn't work well in the 5.7L. My OEM experience tells me it was strictly a cost issue on why they didn't use the expensive plugs in the 5.7.

Thoughts?
to be honest, i don't know. one would think that if copper plugs worked good, then platinum or iridium plugs should work better.

it could be a cost issue. platinum and iridium plugs run at about twice the cost if not more than standard copper plugs.
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Old 08-03-2014, 11:10 AM   #102
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Platinum and iridium plugs do not conduct electricity as well as copper. The hotter the spark the more metal transferred the reason copper plugs wear out sooner than others. If you wait until 100,000 plus miles to change your plugs there is a very good chance of having them seize up in the head (some vehicle models are worse than others) I have bought a few guns and a lot of ammo from the money I have made pulling heads because of this. Modern engines run cooler than there predecessors do to NO emmisions.

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Old 08-03-2014, 03:44 PM   #103
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to be honest, i don't know. one would think that if copper plugs worked good, then platinum or iridium plugs should work better.

it could be a cost issue. platinum and iridium plugs run at about twice the cost if not more than standard copper plugs.
There have been some somewhat knowledgeable people suggesting that running the higher cost plugs is a bad thing. I know there are issues with the Al heads with some recommending anti sieze (which I'm not a fan of as it can allow for over torquing), BUT IDK. I will probably change plugs later this winter, and I'm at 25k miles right now and the coppers are recommended to change at 30k miles.
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Old 08-03-2014, 04:40 PM   #104
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There have been some somewhat knowledgeable people suggesting that running the higher cost plugs is a bad thing. I know there are issues with the Al heads with some recommending anti sieze (which I'm not a fan of as it can allow for over torquing), BUT IDK. I will probably change plugs later this winter, and I'm at 25k miles right now and the coppers are recommended to change at 30k miles.
my general rule of thumb is to go by the manufacturers recommendations. they built the vehicle, so they should have the best idea as to how best to maintain it.

i use anti-seize on just about everything, especially if the materials are dis-similiar. aluminum threads are very easy to gall and cross-thread. anywhere a fastener is exposed to heat or corrosion.
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Old 08-03-2014, 04:48 PM   #105
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I think the reason copper erodes more quickly than platinum, iridium, etc., is due to softness, and the higher corrosion potential of copper, not the spark being hotter.

I haven't really studied it much for spark plugs, but do know that it is one of the issues in contacts for electric motors, and switch gear.


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Old 08-03-2014, 05:13 PM   #106
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I think the reason copper erodes more quickly than platinum, iridium, etc., is due to softness, and the higher corrosion potential of copper, not the spark being hotter.

I haven't really studied it much for spark plugs, but do know that it is one of the issues in contacts for electric motors, and switch gear.


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that sounds possible. in lots of high end electronics, gold, platinum and silver are used a lot because they conduct electricity better with less resistance. in electricity, resistance equals heat build-up in the circuit.

the source i linked, showed at room temperature, that copper was at about equal with platinum, but under extreme heat, platinum was more resistant to the heat at conducting electricity. what is the temperature of a combustion chamber? a couple thousand degrees above room temperature would be my guess.

my guess it could be a combination of cost vs. lower maintenance ratio. if you only had to replace the spark plugs every 100K miles and drove an average of 15K miles per year, that works out to only replacing those spark plugs about every 6.6 years. at about $3-7 per plug on a v-8 engine that is $24-56 worth of plugs, divided by 6.6 years, that equals about $3.60-8.50 per year in plug costs.
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Old 08-03-2014, 05:49 PM   #107
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The other issue is accessability. My minivan is the first vehicle I have owned that actually gets worked on by a mechanic.

The engine is so squeezed in there it is nearly impossible to work on. To change the two right hand spark plugs, you have to come in from the bottom, and remove the fender liner, then the serpentine belt and alternator. Not too bad if you own a lift and can raise the vehicle and work under it. It is an all day project if you do it in the driveway with jack stands and a creeper.

One of the things about the internet is that there are a lot of sites that track things like cost per mile, annual cost of ownership, and lifetime value if vehicles.

So if you are specifying plugs for something that is hard to work on, you spec the longest lasting components you can.


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Old 08-03-2014, 06:20 PM   #108
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It isn't false and Wikipedia isn't proof. NO is created at higher temps and due to that modern cars run cooler and anyone that has welded can tell you higher heat ie more spark equals more metal transfer. The reason for other than copper plugs are to run engines until there warranty is no longer in effect and for advertising purposes. Our car cost less to run 100,000 miles than our competitors.
Not to pick nits but, it's NOx (you excluded NO2)

Are you (L1) certified by chance?
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Old 08-03-2014, 06:38 PM   #109
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I think the reason copper erodes more quickly than platinum, iridium, etc., is due to softness, and the higher corrosion potential of copper, not the spark being hotter.

I haven't really studied it much for spark plugs, but do know that it is one of the issues in contacts for electric motors, and switch gear.
Iridium has a very high melting point and is one of the most corrosion resistant metals there is. Thus their 100,000 mile life span. But I agree that car companies have gone to their use mostly to be able to advertise their vehicles as "low maintenance" rather than any performance standards - IMO.

One of the car companies I worked for used to list EFI fuel filters at 60K miles on the maintenance schedule. Now they are "lifetime" and never need to be replaced under "normal" service!
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Old 08-04-2014, 01:48 AM   #110
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my general rule of thumb is to go by the manufacturers recommendations. they built the vehicle, so they should have the best idea as to how best to maintain it.

i use anti-seize on just about everything, especially if the materials are dis-similiar. aluminum threads are very easy to gall and cross-thread. anywhere a fastener is exposed to heat or corrosion.
Be careful with anti seize, as you can over stretch a bolt with anti seize having lubricating properties. A really good example is on wheel studs. They will over stretch and weaken when torqued to the proper torque and anti seize.
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