My heep has 130k on it. The last time I changed out the spark plugs was at 50k. It was running fine, no red flags or issues, I just thought it wise to change them out before I had a problem. I?ve read many threads on various forums about which brand & model plug folks are using, but, there always seemed to be conflict. So, I just went to the Jeep dealer in town, paid their prices.
2005 Jeep Tj, 4.0/I-6, 6spd
Plugs; Mopar/NGK ZFR5N
Cost; $22.20 ($3.70 each?)
Tax; $ 2.06
The factory service manual (FSM) indicates the following;
Plug Gap; .030 to .035
Plug Torque; 22ft lbs
The coil rail torque in the FSM was unclear to me. Best I could discern was 20 ft/lbs. Also, I put a light coat of anti seize on the threads of each plug, and the 4 coil rail bolts. Hope that wasn't a screw up...anyway...
I set out to change them. I started at the rear of the engine, closest to the fire wall, and for the purposes of this write up I?ll call that one #1. Here?s what I found;
The 1st plug gap had grown to .070
The 2nd plug gap had grown to .053
The 3td plug gap had grown to .058
The 4th plug gap had grown to .067
The 5th plug gap had grown to .070
The 6th (closest to the radiator/front) gap had grown to .055
The 6th plug appears to different from the others. Any thoughts as to what the conditions on the electrode(s) suggest?
Last, my heep overheated a few months ago while up at Naches/Manastash as a result of a blown, plastic cap on the flush/fill kit adapter kit (Prestone) that I installed a few years ago. It actually overheated 3 or 4 times total that day before I got it solved. My thought is the conditions of the majority of the plugs showed some indication of the overheating/preignition episode(s). But, I just guessing. What can you guys tell by looking at these photos?