Changing the spark plugs?

The iridium spark plug change is a fairly simple process and there are several posts about how to do this. You need access to the correct tools including extensions. You'll probably need a 5" extension depending upon your socket wrench and spark plug socket. Remove the relay box attached to the cowl before you start, to improve access to the spark plugs.

Besides that, my two suggestions are:

- that you use only the correct NGK or Denso iridium spark plug as specified in the owner's manual. Do not cheap out with a substitute platinum plug.
- when reconnecting the spark igniter wiring harness connectors, make sure that the connectors are secure. A loose connector will result in engine misfire.

 

After roughly how many miles should I replace the original plugs? Currently I'm planning on doing them at about 125000 miles (200000 km). Does that sound about right?

 

I wouldn't wait that long. I'd do it at 25k.

The problem with the spark plugs is NOT that they will not last.

You basically have a plated steel screw going into a tapped cast aluminum threaded hole. At 12.5 k, the threads might be frozen in the holes.

An anti-seize lube needs to be applied to the threads.

 

In the US, 120K miles is the normal service interval. I do not think it is necessary to replace the plugs before then unless you have an engine misfire problem.

If you are concerned about the plugs sticking to the spark plug holes, you can remove them for inspection at 60K miles.

Another poster recently provided a link to an NGK advisory which suggested that anti-seize lube is not required on that manufacturer's spark plugs where the threads have a plated finish. The lube will result in excessive torque being applied which can damage the plugs.

 

Thanks Patrick. Yeah I've got a new set of the NGK irridium plugs read to go. I'm almost at 150000 km at the moment and everything is still running sweet. My planned maintenance is at 150k, 165k, 180k and 195k km, so I think I'll leave them for the 195000 km service.

I know some people have reported the plugs being a bit tight after being in for so long, but after 150000 km I guess mine are as tight now as they'll ever be, so I might as well wait for the planned schedule. Also, with the nickle platted threads, they may get tight but if cranked hard enough then they still should release without binding and gouging anything. That's what I'm hoping anyway.

The main thing I've found to be important when removing difficult spark plugs is to always brace the drive end of the socket wrench with enough counter-force to make sure that the applied torque is completely axial, to avoid any transverse twisting that can break off the plug.

 

Yes, I can be counted in the crowd that noticed the Prius spark plugs, after a long service life, are tight. It's not so much that the plug is difficult to start turning. Rather, after you start rotating the plug counter-clockwise, the amount of force required to overcome the thread friction seems greater than "normal" even after a couple of rotations.

I agree with your comment that it is necessary to avoid a transverse force on the spark plug. A careless application of force combined with use of a regular long socket (w/o the rubber spark plug insert) will definitely result in a snapped porcelain tail.

 

I'm about to change out spark plugs for the first time on a 2006 Prius that has 93,000 miles. I bought Denso Iridium Longlife plugs, #SK16R11 from amazon.com for about $9 each.

I will NOT be applying anti-seize compound to the threads, based on what I've read here on PC and information from Denso and NGK. Specifically, the first caution note from this Denso webpage (DENSO SPARK PLUGS) states "Do not use a thread lubricant". Likewise, NGK has a detailed warning about using anti-seize compound on plugs that have a metal shell plating, which provides the lubrication for these plugs going into an aluminum cylinder head. To my eye, the Denso plugs I have here have a metal shell plating -- the threads are silver and shimmer as if there's an uneven coating (i.e., not bare metal). And as stated above, Denso says not to use thread lubricant.

If anyone has a Toyota shop manual for the Gen II Prius that specifically instructs the use of anti-seize compound on iridium plugs, please post the relevant pages. Otherwise, I think PC folks who say anti-seize must be used on Denso and NGK iridium plugs are wrong. And worse, could be inviting damage to other PC members' plugs and head.

 

The last paragraph on page one throws up possible confusion. It states that the coating breaks away from the thread when the plug is removed. If the advise of Toyota is followed and the plugs removed and refitted at 60,000 miles would Toyota's advise on using anti seize compound still hold good? or would it be better not to remove the plugs at 60,000?

 

My take-away from this discussion so far, is it makes me wonder about the risk-benefit of using anti-seize compound. The thread plating of the Denso plugs is supposed to provide an anti-seize feature, but apparently only on initial installation. Subsequent removal, inspection, and replacement somehow deteriorates this feature. According to manuals, the plug is supposed to be torqued to 156 in-lb which converts to 13 ft-lb. Not a lot of force compared to other engine tightening torques. I wouldn't think any additional "lubrication" provided by anti-seize compound would result in over-tightening at this level of torque, and possible damage to the threads. It would be better than backing out a plug and stripping aluminum threads. My engine is at 126K now with no ignition hiccups or indications of necessary plug replacement. I did remove and inspect the number 2 plug a couple weeks ago just to confirm the plug manufacturer and part number for eventual replacement. When I replaced it, I swabbed a small amount of anti-seize in the middle of the threads and worked it back and forth before the final torque. I do plan on plug replacement soon, with the exact part specification, and will treat the remaining plug holes (1, 3, and 4) with a small amount of anti-seize. This just seems to me like a "better safe than sorry" situation.

 

13 ft-lbs is low; Honda is/still recommends 13 ft-lbs and has had issues with the spark plugs backing out on some engine families.

I generally follow the spark plug manufacturer's recommendations, and NGK recommends 18-21 ft-lbs for a 14mm plug. I torque to 18 ft-lbs using an inch-lb torque wrench and no anti-seize.

 

I can understand your position on not using anti-seize with new plugs, but what is your position with Toyota recommending removing the plugs for inspection at 60,000 miles then re fitting with anti-seize? As the plug manufactures say there anti-seize coating is removed when the plug is removed. So Toyota seem to have things correct when re fitting plugs.

 

Where in the manual does it suggest to remove plugs for inspection at 60k miles?

The plugs have a one-time use crush washer that provides the proper seal. I would never remove the plugs unless I was planning to replace them.


iPhone ?

 

In the UK service book it says 60,000 miles remove spark plugs and inspect.

 

I do not believe that there is such a recommendation in the US manual.


iPhone ?

 

I believe some folks are still back in the 50's with plugs. They probably change oil every 3000 miles as well! H

 

Come on Harold some have gone to 5000 miles reluctantly it seems.

 

Better get Nissan on board, they're still at 3750 or 3 months for almost every conceivable driver profile.

 

It always amazes me how different service/oil change intervals are between countries. The last Nissan I had probably 25 years ago now "a Nissan Bluebird" even back then in the UK was 10,000 miles.

 

I love pictures so here is a good link to view before you change plugs. I still find the argument about the crush ring and anti seize unresolved!
Toyota Prius 2006 Spark Plug Change