As I approach 80K on both of my Duratecs I started looking at spark plugs on Rockauto. I notice that they have a 'star system' (like the one used on some motor oil jugs) for 'durabilty', MPG etc... I understand that Iridium, platinum etc..are more durable than regular copper plugs but I'm not sure I believe they could have a noticeable effect on MPG. Thoughts and experiences?
Can spark plug type really effect MPG?
- Thread starter pbm
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They can have measurable difference, may not notice it with normal driving. Wider gap usually allows to burn fuel better so less fuel needed to make same power, at least in theory 
Maybe to small a gap might produce a barely noticeable mileage hit? My 2.0l had one plug where the center electrode broke deep down some how and was resting on the side electrode, producing only an intermittent and barely noticeable misfire(no error code), and maybe a 5% mileage hit.
I just went with the $5/plug champion platinums, I figure they will go to the end, and if not, they are easy to change.
I just went with the $5/plug champion platinums, I figure they will go to the end, and if not, they are easy to change.
Misfires make gas mileage worse as injected fuel doesn't ignite in a cylinder and the cylinder doesn't contribute to power production.
My opinion is that all things being equal, for example take a set of copper plugs, Platinum plugs and Iridium plugs, gap them all correctly to spec and install. I don't think you will see any difference in MPG or performance. The plug just delivers spark, the amount from the coils will be the same to all the plug types. Will there be small measurable gains in output across these 3 plug types? Perhaps but so low you won't see any measurable difference in power or MPG's. I think the only benefit to the other plugs over copper is longevity. I am probably wrong, I have read all the different articles on plugs and the tech they offer but I still say a spark is spark at the end of the day. I do run whatever plug style a vehicle is spec's for and pretty much always upgrade a copper spec vehicle to platinum or better for the longer life. Thru the last 30+yrs I have seen wonder plugs come and go...2,3, 4 prongs and such and never had good luck vs a standard single prong plug. I still have butt burn over bosch platinum +2, +4 and Fusion plugs and misfires right out of the box.
Rock Auto....
"Star" = "Sale"
"Heart" = "One of our most popular parts"
"Star" = "Sale"
"Heart" = "One of our most popular parts"
All mine get Copper or platinum. My Dodge Ram says to use 2 copper plugs/ cylinder. They always look new when I replace them at the 30k interval. My guess is they want them changed at that time so they don't weld themselves in the head.
A spark plug that produces a more energetic spark, like one with a larger gap, will cause a faster flame growth. This has a similar effect to advancing the ignition timing, since most of the combustion will occur sooner.
The result of this is more power and better efficiency at moderate to high engine loads where more advanced ignition timing is beneficial. The likelihood of knock will be increased though. More spark energy at low engine loads might actually hurt efficiency though, since the ignition timing here should already be tuned to achieve maximum brake torque with the recommended plugs.
Here's a figure from a study that compared traditional copper plugs (Type A), to a platinum/iridium (Type B), and a plug with three ground electrodes (Type C). With air fuel ratios near stoiciometric (1.0), there was no significant efficiency improvement, but the platinum/iridium type plug performed much better in very lean conditions.
Here's what the flame looks like for each plug. The iridium/platinum produced the fastest flame growth in lean conditions, but not significantly faster near stoichiometric AFRs. The three-electrode plug performed the worst, but its gap was smaller than the other two.
The result of this is more power and better efficiency at moderate to high engine loads where more advanced ignition timing is beneficial. The likelihood of knock will be increased though. More spark energy at low engine loads might actually hurt efficiency though, since the ignition timing here should already be tuned to achieve maximum brake torque with the recommended plugs.
Here's a figure from a study that compared traditional copper plugs (Type A), to a platinum/iridium (Type B), and a plug with three ground electrodes (Type C). With air fuel ratios near stoiciometric (1.0), there was no significant efficiency improvement, but the platinum/iridium type plug performed much better in very lean conditions.
Here's what the flame looks like for each plug. The iridium/platinum produced the fastest flame growth in lean conditions, but not significantly faster near stoichiometric AFRs. The three-electrode plug performed the worst, but its gap was smaller than the other two.
I ran platinum and copper plugs in my 2000 VW GTI. I didn't notice any difference in mpg with either.
An old trick I heard from my Dad waaaaay back in the day for stubborn plugs was to just barely tighten each old plug before loosening them. No idea if there was any science behind it, but it has always worked for me.
Back in ye olde times spark plug gap was apart of your tune
Too hot and you might burn through a cylinder, too cold and you might misfire or get sooty.
Something I’ve wondered about is when one cylinder is low compression has anyone ever adjusted that one to a hotter plug to even things out?
Too hot and you might burn through a cylinder, too cold and you might misfire or get sooty.
Something I’ve wondered about is when one cylinder is low compression has anyone ever adjusted that one to a hotter plug to even things out?
I had a hard-starting 1976 Honda Civic. Carbed.
I clipped the side electrode back, to give the flame kernel a straighter shot to the combustion chamber. It seemed to work.
I now buy Ruthenium plugs, with the hope that the thinner wires provide less blockage of fresh charge, in lieu of indexing the plugs. With DI, I doubt there would be any noticeable difference either way.
I clipped the side electrode back, to give the flame kernel a straighter shot to the combustion chamber. It seemed to work.
I now buy Ruthenium plugs, with the hope that the thinner wires provide less blockage of fresh charge, in lieu of indexing the plugs. With DI, I doubt there would be any noticeable difference either way.
Which is why; in part, it’s best to replace even Long Life Iridium plugs on a maintenance schedule rather than waiting for obvious running issues. It’s a chance to see conditions in each cylinder and while they still will run it is not long optimal for all components. Could an ignition coil burn out faster in these situations?
This is the 'star system' that I am referring to in my OP. I'm thinking that the mpg difference is very minimal if at all between plug types. If I had a V6 or V8 with hard to reach rear plugs I'd go with the longer durability plugs but in an easy to reach straight 4 cylinder I'm less worried about 'durability'.
Thanks for all the replies.
burbguy82
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I agree, factory plugs work the best, and changed at the right interval.
I think so to the burn out faster question, more power is more power More power means more heat and so on.. Larger, less resistance wires would help. I run 8mm on everything I have.
I would add that the plug does not make the spark, it conveys the energy. The coil makes the spark.
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