Question about Spark Plugs

[imported_inspire]

I figured if anybody would know, it would be you guys. In my never-ending quest to pinch pennies, I came to the question of spark plugs - particularly are Bosch Platinums (platinum core) worth the added cost of their half-price counterparts, Bosch Supers (copper core)? How do the electrical properties of each element compare to one another?

 

[Pulsar]

Platinum spark plug's electrodes will, in general, last longer than copper because platinum is a denser material.

Some people claim that platinum spark plugs require larger gaps than copper etc. However, that has never made sense to me because the dialetric of air is not determined by the electrode, and the heat of the spark is a result of the voltage required to break down the dialetric of air to get the spark.

Platinum spark plugs are used by manufacturers that are trying to get to 100k before the first real "tune up". Copper plugs are generally not durable enough to do that.

If you are going to pinch pennies, go with the copper. There is every likelihood that they will last for the entire time you own the car.

 

[CycloWizard]

I don't think the density of the material has much to do with its durability. I'm not a metals expert, but I think the reason platinum is superior is because it is more resistant to corrosion. Corroded metals are very poor conductors, so a corroded plug will give much poorer performance and mileage. How quickly a plug will corrode depends on your engine and its condition. In general, I've had to replace copper plugs about 3 times as often as platinum plugs. That said, copper plugs are usually good for 2-3 years before anything significant happens to them.

 

[imported_inspire]

Thatnks for the replies guys - The most surprising thing is that I try to change my plugs every 12k miles - which is about every 6 months for me. I suppose it depends on how much you drive as to how 'long' (in terms of time) your spark plugs will last.

 

[CycloWizard]

Originally posted by: inspire
Thatnks for the replies guys - The most surprising thing is that I try to change my plugs every 12k miles - which is about every 6 months for me. I suppose it depends on how much you drive as to how 'long' (in terms of time) your spark plugs will last.

If your engine is worn, you need to change them more often. This is because combustion products slip past the piston rings into the combustion chamber and deposit on the plugs, inducing corrosion.

 

[Pulsar]

Cyclo, you are correct, corrosion is the primary issue that drives the electrode material. My bad. I had to go back and look it up.

 

[wirelessenabled]

In my Subaru platinums don't work at all. Missing etc. Physics says this shouldn't be true but there you are.

I use Subaru OEM which are rebadged NGK copper plugs and they work great for about 30K miles.

 

[OS]

Q. What makes Iridium better?
A. Until recently, platinum was considered the best material to use on the top of an electrode because of its durability. However, Iridium is 6 times harder, 8 times stronger, and has a melting point 1200 degrees higher than platinum. Put that into a harsh environment such as an engine piston chamber, and you have a spark plug that can resist wear much better than platinum. Additionally, the DENSO Iridium Power alloy is so durable; it allowed our engineers to produce the world?s smallest center electrode (.4mm) which reduces the voltage requirements, concentrating its sparking power. Also, its smaller size, combined with the tapered U-Groove ground electrode, allows more room for the flame kernel to develop and produce a more efficient combustion.

iridium spark plug considerations

 

[CycloWizard]

Originally posted by: wirelessenabled
In my Subaru platinums don't work at all. Missing etc. Physics says this shouldn't be true but there you are.

Probably incorrect gapping. Platinum plugs come pre-gapped, so the guy at the parts store (or the garage) probably gave you the wrong ones.