Use hotter plugs to avoid sooting?

**torqueless** · 01-30-2013 07:11 AM

I have a 2002 wrx wagon.

At 30K I had to replace spark plug #2 because of misfire. At 62K I had to replace plugs 1 and 3 again because of misfire (odb2: P0301, P0303). The plugs have carbon soot. Incredibly the two plugs failed within minutes of each other. I was able to limp home on two cylinders.

I also tend to drive at low RPM (most of the time around 2000 RPM) and often drive short trips. I understand this contributes to the carbon sooting.

photos of failed spark plugs

If I rev the engine to 3000 rpm for a few seconds at the end of each short trip, would that help? According to NGK web site, hotter temperature is required to burn off the carbon soot.

In the future, is it advisable to use a plug with hotter heat range? The OEM plug is NGK PFR6G, perhaps I should try PFR5G?

**T0rque** · 01-30-2013 07:54 AM

Spark plugs in a 2002 should be replaced every 30k with a fuel filter. You could use a step hotter spark plug to prevent the issue but it seems like you are getting more than 30k out of your spark plugs and you shouldn't be. Also hope you are using only premium fuel and of decent quality.

**Mikie13** · 01-30-2013 08:18 AM

Why do you drive bogging the engine down?

**Ingo** · 01-30-2013 11:06 AM

Originally Posted by T0rque

Spark plugs in a 2002 should be replaced every 30k with a fuel filter. You could use a step hotter spark plug to prevent the issue but it seems like you are getting more than 30k out of your spark plugs and you shouldn't be. Also hope you are using only premium fuel and of decent quality.

Wouldn't that make the car not run at all? Sorry, couldn't resist...

**T0rque** · 01-30-2013 12:46 PM

What?

**Donkey** · 01-30-2013 02:18 PM

I was under the impression the 02 service interval for the plugs is 60K. There should be no reason to go any hotter than stock,especially on a forced induction motor. Not to mention in this case you are just putting a band aid on the problem. If you are fouling plugs then there is an issue at hand.

**UEDan** · 01-30-2013 02:19 PM

Originally Posted by T0rque

What?

You wanna stick a fuel filter in a spark plug hole? Effin grammar nazi =P

**T0rque** · 01-30-2013 02:24 PM

Afaik the interval on 2.0s is 30k because they are a standard plug. The newer 2.5s and the STi is 60k

**T0rque** · 01-30-2013 02:25 PM

Originally Posted by UEDan

You wanna stick a fuel filter in a spark plug hole? Effin grammar nazi =P

Who in the **** would read it that way.. GTFO

**Heide264** · 01-30-2013 02:28 PM

Originally Posted by T0rque

Who in the **** would read it that way.. GTFO

I did, ha..

**Donkey** · 01-30-2013 02:28 PM

Originally Posted by T0rque

Afaik the interval on 2.0s is 30k because they are a standard plug. The newer 2.5s and the STi is 60k

Not according to the factory service manual. The 02 WRX came with platinum plugs with the change interval @ 60k while the 2.5 n/a impreza has a 30k plug change interval.

**T0rque** · 01-30-2013 02:30 PM

Gotcha, then donkey is right, something else is the problem fouling them that often.

**nsibanez** · 01-30-2013 06:58 PM

why would you only replace 1 or 2 spark plugs at once? just curious
don't go too hot because you dont want to have pre ignition

**Anub1s** · 01-30-2013 07:26 PM

Originally Posted by nsibanez

why would you only replace 1 or 2 spark plugs at once? just curious
don't go too hot because you dont want to have pre ignition

Because some people don't know about maintenance intervals, or basic car maintenance guidelines.

**99pgpgt** · 01-30-2013 08:39 PM

If it is stock, then run stock plugs.

If modded, run the hottest plug you can run safely.

People are misinformed many times on how cold or how hot to go with plugs.