Sometimes I install dry, more so with new.
Is it really necessary to coat the threads. Probably not, as Denso does not specifically recommend nor does Toyota. IMO Denso has designed the threads not to seize with aluminum and cast iron heads in mind.
When I do install wet, I use standard copper anti seize, but very sparingly. Sparingly because I do have some concern with particles getting in combustion chamber. So to easy my concerns, I do not put any on first 3 to 5 threads. Once I've rubbed a small amount on the upper threads I wipe off and blow off with compressed air, leaving just a very thin layer.
This may be considered
lubricating the threads, all be very lightly. So torque to the factory spec may mean I'm over torquing. But I'm good with over torquing, as I've been finding loose spark plugs. Also I'll still be within Denso torque range. Torquing procedure is also based on new spark plugs, which washer has not been crushed and threads are clean/smooth. So using a torque wrench becomes even more import when installing used. I do wire brush the threads of used plugs, then with that little bit of lube, gets me close to new condition IMHO.
I don't use oil on threads, as I'm concerned (don't know) that that it will break down to carbon deposit making removal difficult. If I was to oil I go with synthetic oil for sure.
From Dense:
Note: "The installation torque values shown above apply to new spark plugs without lubricating the threads. If threads are lubricated, the torque value should be reduced by approximate 1/3 to avoid overtightening."
I've added inspection of spark plugs to my PM schedule at every 30K miles. Number one reason for this is; I'm finding loose plugs. Second reason is to inspection gap, once gap starts to grow I replace them to
protect coils from overheating.
Coils bolt torque 66in-lbf (That is
inch not foot lb.)
I've been just using Toyota recommended
Denso SK20R11
0.7mm Iridium so far. You can buy from Lexus or Toyota Dealer and pay a premium, or find your best deal at any authorized Denso Wholesaler or retailer.
I've been considering using one of the newer Denso
Power 0.4mm Iridium or
Iridium TT 0.4 millimeter spark plugs. Denso recently change their web page to read "last longer than 100K miles" on these 0.4mm. These plugs promise lower power use to achieve a great spark. This suggest a better burn of fuel with cooler running coils. With heat be the number one killer of coils, these could extend usable life of our very pricy Denso coils. The TT's may be the coolest running as they pre come gapped at .04in whereas they others are pre gapped to .44in.
Introducing the New DENSO Iridium TT Spark Plug
I like replacing spark plugs with timing belt job at 90K miles, just to align timing of jobs.
