Gunked up spark plug (First spark plugs change at 181k)

Hi. I recently got my first truck/Taco and I've been doing all the DIY maintenance to make sure she's up to date on everything and today I changed the spark plugs.

From what I've gathered, for some obscure reason, Toyota puts three NGKs and three Densos in their V6s at the factory which leads me to believe that the previous owner never changed them. The first one I pulled out was all gunked up with what I believe is oil? Im relatively new to car maintenance beyond a basic oil change so I dont know if this is harmless or indicative of an issue. Two of the SPs were gunked up but the rest were fine. Any feedback would be greatly appreciated.

Also, there seems to be a fair amount of carbon built up on the cylinder heads but again, Im not experienced enough to know for sure

 

For 181k miles the Denso looks like what I'd expect. On the NGK, it's hard to tell if that is rust or dried oil on the plugs' hex and shoulder, otherwise, it looks normal for the age. There is a seal in the valve cover in that area and it may be leaking. Did they come out easy? With aluminum heads, if there's any resistance upon removal I spray a penetrating oil down the hole and work the plug out slowly turning in and out until it loosens up.

 

The Denso yes. Barely harder than the other 4 clean ones. The NGK was very hard to break loose though

 

Then I assume you have all the new plugs installed and you didn't strip the threads in the head on the NGK one. In the future, remember aluminum heads are easy to strip the threads. Spraying penetrating oil down the hole and letting it set for a bit, then working the plug in and out loosens up the carbon buildup on the plug threads minimizing the threads in the head from striping. So far it hasn't failed me.

 

For the mileage and time they've been in there, they really don't look too bad, even the oil.
Put the new ones in and drive it. If you're not getting any misfires, you're fine.
I've seen them wetter.

 

If the prior owner never changed plugs in 181000 miles he probably didn’t do any other maintenance either. I would have been very leery and hesitant to buy that truck under those circumstances. You may have bought a project.

 

Its odd because he always had the truck serviced at the toyota dealership where he bought it in 2013. Theres even the sticker in my window to remind me of the next appointment. Maybe the dealership also puts three NGKs and three Densos on each side, in which case they wouldn't be the factory plugs. Overall though, the truck is in great shape for its mileage from what ive seen. I checked the differentials and transfer case too when I changed the plugs and that had been serviced recently

 

Very unlikely that anyone who previously serviced the truck would put 2 different brands of spark plugs in.

 

If you're not feeling misfires or throwing codes then you dodged a bullet, often the increased gap and resistance of high mileage plugs can cause the stick coil to fail. Swap 'em and drive on, no big deal. Congrats on the new truck!

 

those are clean looking to me, gap and go

Mine made it a long time until one started to make it sputter at idle at 211k

 

No misfires, no check engine, nothing. The truck ran perfectly with the old plugs and started immediately even in -9 degrees weather. I never would have guessed that they were that worn out. That's why I wanted a Toyota!

 

No, don't gap and go. The electrode is too far eroded for that. At this mileage the valve cover gasket hardens and is likely the cause of the wetter plugs. Most folks know to get an oil change. Many have little clue as to other services; they address them as things break.

 

For some reason I thought some folks were encountering the 2 different spark pugs from the factory. It's been mentioned around here somewhere before if I'm not mistaken.

 

I changed them and ill check the gasket too. Thanks for the tip

 

Thats what I've read somewhere on here too. Something about Toyota having a deal with both NGK and Denso iirc

 

Not to discourage preventive maintenance but if your plugs aren't 'wet' with oil (on the exposed portion), you have some time.

 

Seriously?

 

I would add that spark plug removal with aluminum heads should only be performed on a cold engine: "overnight cold": especially with plugs that have been in place for 100,000+ miles.

 

I know this is controversial and I am not one to put things off, but how may threads have you seen that start out as a 'changing sparkplugs' thread to, 'I've broken a coil bolt and a day later...".
Just saying, if the person asking isn't somewhat mechanically inclined, I don't think it's right to scare him into thinking he needs to change his valve cover gaskets or his truck will self destruct.
His next thread will be about rough idle because he broke the vacuum nipple off the back of the intake.....

 

It is a common "feature" and AFAIK ran through, and to the end of, the entire 2nd gen 4.0L V6 production in 2015. When I pulled my plugs at around 120,000 they were all Denso plugs (K20HR-U11) which turned out to have been in there for about 115,000 miles according to service records. see pic: