spark plugs


Old 10-19-05, 08:45 PM
Thread Starter
Join Date: Sep 2002
Location: illinois
Posts: 67
spark plugs

I know platinum plugs are good for up to 100k,but what about regular plugs?I have a 94chevy lumina,manual says to change every 30k.First time I changed late at 40k with no problems,last time changed at 45k car was still running good no misfire,no loss in power,no drop in miles per gallon.i'm at 45k again and wandering if i should change plugs or push it longer,running great.How long do non-platinum plugs last?
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Old 10-20-05, 07:48 AM
Join Date: Oct 2000
Location: Livonia, Michigan
Posts: 923
You've been fortunate to have an engine that runs well this long without fouling your plugs. I'd still replace the plugs as preventive maintenance. Regular plugs don't last forever.... the gap widens, the center electrode erodes further down into the ceramic, and the ceramic gets fouled with conductive material. All these conditions make the plug less robust and prone to problems should there be other problems with the ignition.

In real world application, platinum-tipped plugs don't last 100K. They're typically good to 60-80K.

Some engines have problems when platinum plugs are installed in place of OEM regular plugs, so I wouldn't recommend platinum plugs for you.
Old 10-20-05, 12:59 PM
Join Date: Sep 2004
Posts: 238
they last almost forever

Think about it! Who are the biggest cheerleaders for spark plug replacement? Yes, the folks who make and sell plugs.

In '97 I replaced the original plugs on my '94 Taurus when it had about 45k. I knew I put in platinum plugs, so I did not pull them until this year after another 110K. I was surprised when they were not platinum. The positive electrode was worn all the way back to the ceramic insulator. I did not measure the gap but it looked to be at least 3x the spec. I saved the plugs, since I had heard for years to be anal about changing the plugs. The car never started poorly, ran badly or had poor mileage. After changing the plugs, the car ran no differently.

I have never seen conductive material deposited on the insulator. I would guess more than 99% of the eroded electrode is blown out the tail pipe. If the electrode shorted out, you would not even be asking the question, since you would have no spark from that plug.

Do an experiment. Pull your plugs and widen the gap. After reinstalling them answer your own question. Does the car run any differently?

The second biggest group of cheerleaders or rabid plug changers are the kind that get their panties in a knot about brake pad dust on their wheels, pour degreasers and detergents on their engines and wash it all down the storm drain. They also put stuff on their tires to make them shinny and get a big kick out of spraying throttle body cleaner every other weekend. The world would be a better place if they just stayed in front of the tv, off the road and out of the parts store.
Old 10-20-05, 01:11 PM
Join Date: Oct 2000
Location: Livonia, Michigan
Posts: 923
The conductive material on the insulator is carbon from combustion byproducts.

And, yes, they do last almost forever. But I clean mine instead of replacing by grit blasting. Not everybody has access to a grit blaster to clean their plugs. I discard them after I feel the center electrode has worn far enough down into the ceramic insulator.

Like I said, an old plug is less robust can lead to driveability problems should there be other problems with the ignition.

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