I know that manufacturers are using iridium plugs these days so that they can say the plugs will work 'well enough' for 100,000 miles or what ever the period the EPA (etc.) requires for emissions purposes. It makes me wonder though how often a modern vehicle would benefit form a new set of plugs. I suppose if your changing coil packs, etc. on a higher mileage vehicle you would do plugs while you had things apart as it is cheap (labor wise) to do it then and a bad coil can foul a plug.
My 2011 Ford Ranger has 48K miles now and at 50K I plan on putting in a new set of plugs. The mileage may not warrant it alone but I'm thinking the age of the vehicle warrants it since they are easy to get to. I suppose growing up working on old cars where a new set of copper plugs every 20K miles was a good idea colors my opinion some.
Just wondering what the professional opinion on 'real' plug life is?
If im not mistaken, I think the "health" of the plugs can be resistance tested.. If so, the spark plugs can be tested and cleaned at every service. Lets see what others have to say.
I have been doing some research on ignition systems and I did come across "testing a spark plug". Try a google search if u have some time..
For customers, I generally just go the life recommended in the book. Having said that, if something comes in for a job requiring removing the plugs like a cylinder head job, or a failed associated part like a coil, it's getting a set of plugs too.
Spark plugs are quite a complex subject and one we tend to forget about with long life plugs and modern ignition systems. I have been considering doing a post on spark plugs for a while,
Personally I would say with single platinum or single iridium plugs change before 50,000 miles double platinum or double iridium 80,000 miles.
I would never fit those 4 point Bosch spark plugs you find factory fit on some french cars . Unless there is some unique reason I always fit NGK or second choice Champion but I know Beru, Hitachi and Bosch also make good plugs. Champion also supply own brand spark plugs to companies like Briggs and Stratton, X-Part
When fitting plugs where a manufacturer specifies an exceptionally wide spark plug gap I tend to reduce the gap by 10% and this seems to reduce the number of coil pack insulation failures I see on the cars I service.
Trying a resisstance test on a spark plug is pointless it will only tell you if a spark plug is badly fouled in which case it will have an obvious dead miss anyway.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
These are the official spark plug manuafecturer recommended plug change intervals ---- to they look shorter than those from the car manufacturers.
Champion Official Expected Spark Plug Service Life
Iridium 75,000 mls or 120,000 km
Double Platinum 60,000 mls or 100,000 km
Platinum 38,000 mls or 60,000 km
Double Copper 25,000 mls or 40,000 km
Copper 12,500 mls or 20,000 km
NGK Official Expected Spark Plug Service Life
Laser Iridium 80,000 to 100,000 mls
Iridium 60,000 to 80,000 mls
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
I read once that the recommended service life was based on emissions more than anything else. In other words, the plug works good enough to not cause an emissions issue. I wish I could remember where I read that.
Someone had mentioned testing spark plug resistance, I think maybe they mean the voltage at which the arc occurs. This is tricky as it depends on compression ratio, the fuel mixture, turbulence around plug. I'm guessing the 'shape' of the arc would give you an idea of how it was functioning though rather than an absolute value.
