About sparkplugs

Asked by Mar 07, 2017 at 04:16 AM about the 1999 INFINITI Q45 Touring RWD

Question type: Maintenance & Repair

Recently I had to replace one of the
coils on my 99 Q45 . Was told by a
mechanic friend that I should try
putting the old spark plugs back in
because he believed that the ones I
had replaced them with weren't correct
even though they were the same brand
with the exception of the length. The
new ones were a little longer..,... so at
the end of the day I ended up only
putting 2 of the old ones back on. My
question is , is it a bad idea to mix the
plugs like that and is the length
difference acceptable?

2 Answers


As long as you are saying they are the same brand and type, then yeas you should be ok


If the length is not the same that could be very bad. Are the thread lengths the same? Is the porcelain insulator near the spark gap the same? What are the part numbers? You could have installed a spark plug with the wrong reach or a spark plug that is the wrong heat range. Get those plugs changed for the correct ones.

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