Double ground electrode spark plugs?



Hello all,

I bought a set of 4 spark plugs for my brother’s 1996 Toyota Tercel (0-60 in 4.5 seconds, quarter mile @ 12.9 seconds in case you were wondering…ha ha ha bad joke).

The ones given to me at the NAPA auto parts store were NGK V-Power plugs after I told them what kind of vehicle it was.

Well, after we finished installing them, we noticed a small warning on the engine block indicating to only use double ground electrode spark plugs. I’ve never heard of these…and the ones we installed were the usual single ground electrode plugs.

My questions are, what are these double ground plugs, why/when are they used, and is it safe to keep the single ground plugs we put in?




Toyota used double ground plugs in many cars in the 90’s. They were supposed to be good for 60k miles instead of the usual 30k. If you engine runs fine on the single ground electrode plugs, then by all means use them, just change them after 30k.

The dual ground plugs have the gap beside the center electrode, making them fire sideways, where the regular plug is end firing. Most cars don’t care, a spark is a spark, but we have a Tercel (86) that seems to run better with side firing plugs, even though it originally came with single ground end firing plugs. Its the only vehicle that I have that has responded this way.


You should genererally stay with what is factory recommended in most cases, although that can be tweaked a bit.

JMHO, but I don’t think you will have a problem with these plugs. The double ground electrode plugs were used with Toyota’s ignition system at the time (forget the technical name), but it is called a “wasted spark system”.

Most plugs fire at the top of the compression stroke, but on this system it also fires at the top of the exhaust stroke.
In theory, since the plugs are firing more often the electrodes won’t last as long. It’s not something I think you should worry about.
If you have any concerns pop the plugs back out in a couple of weeks and examine the tips. If they’re light tan in color then that means normal.

The wasted spark system is nothing new; Harley Davidson has been using it on their motorcycles since way back in the 1920s.
Harley Davidson has only used single electrode plugs all this time with no problem.
Even some motor home power generators such as Onan use the wasted spark; with single electrode plugs of course.


Just wanted to say thanks, keith, and ok4450 for your (as usual) excellent and informative advice.

I’ll check the plugs in a couple weeks and see what they look like. I do know the engine is worn; the old spark plugs were covered with a white/grey buildup.

Thanks again.