Spark plug best practices, and quetions

Just did a spark plug job on my 2000 Tundra 4.7L. I bought this 155k mile truck from a dealer last summer, and it had a auction history, and practically no service records other than what I could cobble together from carfax. Very generic information, mostly. As for spark plugs, zero records. So plugs are on my to-do list. The truck appears well maintained, but I have no idea. It runs fantastic with no issues. I've only put 500 or so miles on this in a year, so it was not urgent.

Figured I'd post some tips and questions.
1. For my 2000 and my other 2002 models, the spark plug part number is Denso Part Number: 9091901166, gap to 0.031. Thru Toyota they were about $2 each.
2. Other than unexpected obstacles, the job is extremely easy. You remove 8 screws, carefulyl unhook 8 tabs, remove 8 coilpacks, remove and replace properly gapped plugs and reinstall everything.
3. It's so easy and cheap, there's no reason to not replace these on a reasonable schedule.

A few tips.
1. The plastic tabs are best done, carefully, with a flat head screwdriver at the base of the tab while pushing in at the top of the tab. Very carefully pry, and lift the top with your fingers.

2. The plugs claim to be pre-gapped but they were all incorrect at .025. They correct gap in the manual is .031.

3. I had 1 coil pack separate and the boot was stuck on the plug. I coated it with liquid wrench, let sit for a few minutes, and used two tools to get it out. First, I used a socket extension the same internal diameter, and put it in there until it got suction, and worked it until it seemed to break the attachment to the plug. Then I used one of those free paint can opening wrenches that's about 5 inches long with a little J-hook. It reached just far enough to hook it and pull the trophy out.

4. Always use some liquid break free or liquid wrench when removing plugs, especially on plugs of unknown age and installation (maybe really old, no anti-seize, etc.). It makes the job much easier. Spray on the plug, let soak briefly. Then try to remove. Breaking a plug will be a real potentially expensive headache. A squirt of liquid wrench is worth the step.

5. Lots of debate but I use a small dab of Permatex silver (a aluminum copper material) anti-seize on the threads. I use a old toothbrush to work it in the seams. Just a tiny amount.

6. I put a thin layer of dialectic grease on the ceramic and contact on the top of the plug.

A few questions:
1. Look at these plugs. One is a Denso, and seven NGK iridiums. The Denso was on the coil pack that separated. The iridium gaps are all the same, and the Denso gap is larger.

My theory is the Denso is the factory plug possibly never replaced when the 7 NGK were installed. The installed probably ran into the separated coil pack, and did not fix it or replace it and just left it.

Alternately it's possible they just replaced the old ones all 8 at the same time but with whatever mis-matched they had on hand. And the Denso wore faster. Any observations on these plugs? I'm thinking the NGK are worth keeping in my spare parts box, and a few in the truck emergency box.

2. Look at these cracks in a few of my coil packs. Should these be replaced? I think they probably should be replaced. I'll probably replace several including the one that separated.

 

Yes. Spend the extra for OEM.

 

My first observation is that the combustion properties across all the cylinders is very consistent, so the truck is obviously running well on that count. Very nice.

 

and make sure you get them from a toyota dealer, not Amazon or ebay as they will probably be knock-offs