I was just wondering what the difference in these two Autolite sparkplugs is.I see people using both in their 5.9 magnum motor.

The 3923's are one heat range colder, the 5224's have a "special" tip... no clue what that means. Aside from that, there is no difference in the spec's that I can find.

Welcome to DF.

w/o looking anything up, i was thinking the 3923/3924 was the standard, inexpensive plug with copper core, and the 5523/5524 was had a platinum covered electrode for supposedly longer life.

either will work fine in your truck.

the cooler (shorter) 3923 are supposed to resist pinging a little better when you have a leaking plenum.

Thanks HeyYou and dhvaughan, I don't have any pinging but I am going to do a tune up soon.In fact I don't have any symptoms of a leaking plenum except maybe gas milage,but I have not calculated it yet.I'm going to check the plenum when I do the tune up.