4.0 Spark Plugs Maintenance Denso 20HR-U11 Copper / Changed @ 34k

Hey guys I just changed my copper plugs / 4.0 6cyl. Plugs had about 34k miles. From the pics they're on the worn side gap wise and needed it. Working on the drivers side is always a little like getting a "ship in a bottle" workout but the passenger side is a piece of cake.

They seem to look normal (all plugs look like the one in the pic) and maybe on the rich side. This could be do to the bigger gap though...or is there potentially something else going on..coolant? The reason I ask is that over the last 68k miles I have to occasionally add coolant to the reservoir - I've added exactly 2.5 quarts over 68k miles / since April of 2016 (3 years). Is this normal? Slow leak or typical loss-evaporation? Truck is a 2008 Prerunner Access Cab with 199,500 k miles and running well.

I've been using 89 octane with an occasional premium 91/92. Perhaps I should switch back to regular 87. I don't really notice a difference in gas mileage. In the summer I get occasional detonation under load with 87. That's why I use 89 or higher. Thoughts?

 

The plugs look normal. As far as the coolant loss, that is more than my truck uses and I live in AZ. It doesn't sound outrageous though. At that mileage it could be something as simple as needing a new radiator cap.

 

Sure I'll try that. Thanks!

 

Those plugs are fine, could have gone another 25K easy.

Also, stop wasting your money on 89, feed the truck 87.

 

Thanks for the advise Mike @ octane - will do. I disagree about the plugs though. The gap was way over spec and if I'm going in to re-gap I'd just assume replace the plugs and save the labor time. My time is worth more than the cost of new plugs, but I get your point.

 

plugs look fine, good choice to just replace em.

As far as coolant, its not excessive, i know my truck will have evaporative loss out of the overflow tank here n there. But 08's didnt have any issues with headgaskets so you are probably good, worst case its a waterpump seal or leaky hose, all which will give you plenty of warning.

 

I would think that a head gasket leak would just get worse over time. Perhaps a combo of water pump seal and evaporative. Either way minor issue. Thanks!

 

Nah all good. Can't hurt changing em!

 

Would anyone recommend the denso iridium plugs?

 

Some people would. I would stick with regular old copper plugs. Your not going to see any change in performance, toyota designed this engine with basic simple plugs for a reason. Its just a truck, not a 350Z

 

Good job on plugs they look nominal to me.
U run what ever octane u want if your pinging I say great call on higher octane I hate those pesky holes in my pistons .

 

I see your point. I see the value of staying stock since it’s my daily. I was thinking in terms of spark plug life.

 

Meh.. copper plugs are cheap. I spend more on coffe in 2 days than a set of 6 plugs lol

 

Just think of it as extra-positive crankcase ventilation. Plus you can use 16.7% less fuel!

 

Iridium plugs are not designed to increase performance; they are designed for longevity. Toyota engineers did not test iridium plugs in this engine, but engineers with manufacturers that offer iridium plugs have. Denso and NGK, both partially owned by Toyota offer iridium plugs for the 4.0. There is no logical reason not to use them. I replaced my OEM coppers at 50K with NGK iridiums; I replaced them at 115K, and I now have Denso Long Life iridiums. I probably went a little to much with the NGKs - I pulled them at 80K and had to re-gap them, but truck still was running fine. But, a large gap puts a strain on the coils.

As for the coolant loss, that does seem excessive. You likely have a slow leak/seep, that evaporates before it reaches the ground. Check the weep hole on bottom of water pump; seams along the radiator; radiator hoses; thermostat housing; reservoir, etc...

 

Stick with the copper plugs, they are the best choice.