Now as you may or may not know, the 3.8L comes factory equipped with Champion RE15PL5 Double Platinum spark plugs. The owners manual states the replacement interval for these plugs is 102,000 miles (p.417). I looked at several different spark plug information sources, most claim a ~60,000 mile interval for double platinum plugs. Why do other sources rate this type of plug at 58% of what Chrysler calls for is beyond me.
Anyway, recently I had been noticing that I needed to slip the clutch a little more to get going. This was much
more prevalent the last time I took it out on the trails. As someone who is fairly seasoned with my rig, it usually takes a good bit of load for me to stall it. I stalled it three times within one trail, something wasn't right. The engine was not carrying the load at idle like it should, it was basically shutting off under a decent load..hardly a stumble (even with a 4:1 case).
Comparing my odometer to what the manual stated for my plugs, I figured what the hell and bought a set of plugs. NGKs have been pretty good to me, at $20 for the set...it was worth it. I cleaned the throttle body (for the third time), which was pretty much as clean as you'd want it already and swapped plugs. I went with the single Platinum "G-Power" NGKs (~$3/plug). I didn't care to go back with the double Platinum plugs again, due to the only gain I see is the claimed longer interval. $20 per 30,000 miles or so...is just fine with me. Single Platinum it is.
My mileage bumped up several tenths (according to my inaccurate display, but it is at least consistent). I have gone back to not slipping the clutch as much and it's 4-low loading seems to have improved. I had used the stock plugs to 41% of their rated "lifetime" and saw improvements. That is pretty pathetic (doesn't help that I have never cared for Champion plugs anyway). It took all of ~10-15 mins to swap them out just screwing around.
I am not one to say "go buy new hi-po wires for your minivan engine", today's ignition systems are pretty stellar. However it's pretty sad what Chrysler expects out of these factory plugs, in my opinion. The gap wasn't too bad on the factory plugs (.054" - spec = .050").
These are what the "G-Power" NGKs look like:
Factory plugs; excuse the pictures, I don't have a macro lens!
You can see the leading edge of the electrode has some decent wear on it. Which...shouldn't really happen.