How Likely Will Spark Plugs Seize Up?

Spark plugs are relatively cheap compared to other expensive repairs on a Prius. If you're already removing the windshield cowl to address other areas of maintenance (like EGR cooler cleaning), you should change out the spark plugs while you're in there.

I think spark plug may not seize up in 10 years but the spark plug gap would have changed so changing them out will improve your car's performance and emissions.

 

10 years vs 12 years, seems hardly worth the extra effort. Especially considering the cowl/wiper removal required. If you're going to do an intermediate check, 60K miles (or 6 years) seems sensible. As @JC91006 mentioned, it's good to incorporate EGR clean-out with the cowl/wiper removal.

FWIW, I had a look at ours around 5 years and 50K kms.

I believe the torque spec is for clean/dry threads. If using anti-seize I would use it very sparingly, say apply then wipe off, counting on residual to remain in bottom of threads. And reduce torque (from spec'd 15 foot/pounds) to maybe 13.

You'll need a 14 mm or 9/16" spark plug socket. If it's got a rubber insert (for gripping plug) I'd recommend to tape the junction between socket and extension, to avoid chance of the socket staying with the plug when re-installing.

Attached is some repair manual info on spark plugs. Torque spec on the last page was actually found in a completely different section of the manual, go figure...

 

I will admit I am very cautious and superstitious about removing plugs that have been in there a while. I take it very slowly, and fall back to turning them very slightly back and forth the first moment anything feels like binding.

So far, that has worked out for me (he wrote, knocking on every wooden object in reach). While I have some experience making Heli-coil repairs to other threads in aluminum things, I have so far never had to do that for spark plug threads in a head, and if I never check that one box off my bucket list, that will be ok with me.

 

there have been reports of frozen plugs, and recommendations of at least loosening and retightening at 60k

 

Maybe loosen and retorque at 6 years for factory plugs. But after you DIY plugs and use antiseize - why bother? I guess it would save you on labor if the cowl is off and you're doing another repair...

With quality gas and fuel system cleaners those iridium plugs should last 100k easily.

moto g power ?

 

I ran out of anti-seize and replaced the original plugs with a Gen2 at 170K a few days ago... My perspective/rationalization was that the original set put in for that many miles definitely would be good to use anti-seize and not sure if Toyota does?

But once you're on that second set of plugs you're going to be replacing them sooner than the last set and odds are the car will be at end of lifespan before you need to worry about it again. Although my '07 with 270K is on its third set of plugs.

Lastly, I've done this work on lots of Prius and the more dirty and nasty the engine compartment in general, the more I see signs of rust and corrosion on the upper most parts of the thread where they could seize up.

 

I went to check my plugs on my 2004 Honda, it has only 38,000 miles on it. The plugs are original and I wanted to make sure they didn't seize up. To my surprise, they come out quite easily and the plugs look great for the mileage. Re-torque them and now I won't need to look at them for another few years.

 

I think they don't. I was the first person to look at ours post-factory, and they looked clean/dry. I believe the plug manufacturers do NOT recommend anti-seize, and use some metallic coating on the thread that's supposed to be better, say compared to a regular threaded bolt.

 

Perhaps anti-seize is one of those old time car needs back when the plugs were much more expose to the elements? Kinda like how radiators needed to be flushed and cleaned to prevent corrosion regularly but thanks to better quality materials today radiators no longer fail from corrosion.

 

This is what NGK say in their website:
NGK spark plugs feature trivalent plating. This silver or chrome-colored finish on the threads is designed to provide corrosion resistance against moisture and chemicals. The coating also acts as a release agent during spark plug removal. NGK spark plugs are installed at the factory dry, without lubrication or anti-seize.

Anti-seize can act as a lubricant, altering torque values up to 20 percent, increasing the risk of spark plug thread breakage and/or metal shell stretch. Thread breakage can sometimes involve removing the cylinder head for repair. Metal shell stretch changes the heat rating of the spark plug and can result in serious engine damage caused by pre-ignition. Do not use anti-seize or lubricant on NGK spark plugs. It is completely unnecessary and can be detrimental.

 

I wonder if Denso says similar? Likely.


Addendum:

They say this:

If you apply grease or another screw thread lubricant to the threaded part of the plug, you are liable to tighten the plug to an excessive degree, impairing the integrity of the seal, even if you apply no more than the recommended torque. For this reason, do not coat the plug with screw thread lubricant.

Here:

SPARK PLUG Installation | Basic Knowledge | SPARK PLUG | Automotive Service Parts and Accessories | DENSO Global Website

 

But they have to take into account every situation including new engine build. In old vehicles the threads sometimes so sticky that little antiseize not that dangerous. I would say that if its hard to get plugs out then better apply a little when installing new (or re-installing the old). But if its smooth to loosen then definitely no antiseize

 

Wow... That's impressive... And to think I was worried I ran out of anti-seize and was doing plugs without it... I remember back in my high school days when I worked at an auto shop... So many old cars came in that had spark plugs very much exposed to water and road salt. So I suspect the origins of the need for anti-seize on spark plugs came from these old engines that didn't protect the plugs like they do these days.

 

Sometimes with some cars removal is nerve wrecking, like threads going toast. It amuses me when people say ”so easy, just do it yourself”. Ya right..

my 2010 had plugs replaced at shop among other maintenance stuff. Did not ask whether they’d been stuck or not

 

If it’s a high mileage car pull the cop off and before you touch the plugs take a picture of the sparkplug well with your iPhone. See if there’s any oil in the well. If so put the cop back on and go to the dealer or online and get a valve cover gasket.

 

Yes, DIY is not for the faint of heart... There's a certain amount of initiation/nightmare scenarios you have to face up to and overcome. Professional mechanics deal with this every day and it most often leads to them coming up with a better tool or method to get the job done and that knowledge/experience doesn't come easy for a DIY mechanic.

 

By the same token, a good bit of what you learn doing car DIY you can count as transferable skill, so that's something.

 

Yeah, kinda like owning a truck... You end up having more "friends" because they know who to call when they have to move stuff.

 

Transferable even beyond wrenching, I mean. If you're wrenching on a car and paying attention while you do it, there's a good deal of basic physics, logic, and diagnostic strategy that you are getting good practice in the whole time. Those pay off in a lot of settings and a lot of ways.