How long to wait before spark plug change?

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I know you're not supposed to do it on a hot engine, but how long does the car need to sit before replacing the spark plugs? An hour? 2 hours? If it makes any difference, it's a 2008 Civic LX R18
 
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Ideally it should be done cold. But I have done them after about an hour - just be careful when removing the plugs.
 
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Originally Posted By: tommygunn
I know you're not supposed to do it on a hot engine, but how long does the car need to sit before replacing the spark plugs? An hour? 2 hours? If it makes any difference, it's a 2008 Civic LX R18
How many miles? The iridiums don't need changing until 120k. I changed my brothers 06 civic plugs for the first time at 160k, they looked comparable to new, the electrode was the same length...no mpg or power increase after changing.
 
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Depends on time of year too. In the summer, I'd probably wait at least 3 hours. In the winter time, I'd wait maybe 45 minutes or so.
 

Kestas

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What happens if you take them out hot? Why would they strip? I would expect them to be easier to remove given the thermal expansion of aluminum.
 
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For me 80% of my worry is about stretching the threads in an aluminum head when the engine is hot, I'd say 20% is the increased chance of cross-threading when the engine is hot.
 

tommygunn

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Originally Posted By: 01_celica_gt
How many miles? The iridiums don't need changing until 120k. I changed my brothers 06 civic plugs for the first time at 160k, they looked comparable to new, the electrode was the same length...no mpg or power increase after changing.
The MM says it's time, currently at 104k
 
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I would change them when the engine is stone cold. That is what they taught in school. I don't see how it would make a difference over a warm (not hot) engine though. As for change interval, I'd wait until the car has reached half of its life expectancy regardless of mileage. That way they won't be seized into the head, then you change them and you are good for the rest of the life of the car, you don't need to change them again if they are double Iridium plugs. I would use Techron or PEA a week before the change to soften and remove the carbon on the exposed threads to reduce the chance of stripping the aluminum threads. Use canned air to blow out the spark plug wells, then spray a bit of WD-40 or liquid wrench down there and let it sit for an hour. As the spark plug is coming out the threads suck up the lube and helps ease them out without damaging the head. Install without anti-seize generally with nickel plated threads.
 

tommygunn

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@Falken, and everyone else on here, thanks for the advice so far. The reason I can't do them stone cold is because it's not my car, and the owner doesn't want to stay overnight. I knew about the WD40 though but thanks again. The original NGK plugs shouldn't be seized into the head because they have the metal shell plating (NGK says all of their spark plugs have the anti-seize shell). They will be replaced with the same NGK Laser Iridium, which I have ordered online but they have not arrived yet.
 
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Originally Posted By: Kestas
What happens if you take them out hot? Why would they strip? I would expect them to be easier to remove given the thermal expansion of aluminum.
It can make them easier to remove when hot but only as a last resort. The aluminum is expanded more than the steel plug thats true but that also makes the thread contact area smaller and weaker. If the threads have carbon in them it can tear the threads before it breaks the junk between the threads free. If the plug is so tight it seems inevitable its going to either break or strip then sure get it hot, break it loose then loosen/tighten repeatedly in small steps, many times this will get them out. Never install them hot, easier to strip them and once the aluminum cools it will contract, gripping them so tightly you may not get them out without thread damage. OP As a side note. Penetrating fluid is as useless as spit on plugs and O2 sensors and drain plugs unless they have been cracked loose first. The gas/oil tight seal will not allow even the best of these products through. 2 hours is enough of a wait time. In aluminum it never hurts to use a very small amount of never seize on the threads only (reduce torque by 25%).
 
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I have changed them so hot I needed gloves as well as dead cold in winter, in both aluminum and cast iron heads. Never had any issues due to that. I much prefer to change them in the morning before the engine has been run, though. YMMV.
 
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Originally Posted By: tommygunn
I know you're not supposed to do it on a hot engine, but how long does the car need to sit before replacing the spark plugs? An hour? 2 hours?
When you can leave your hand anywhere on the engine for any length of time without any discomfort, then the the engine is cool enough. That can take anywhere for one hour to four hours, depending on ambient temperature.
 

Patman

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Originally Posted By: barkingspider
I change mine when it's cool to the touch. Safety first.
The plugs on the R18 are all right up top though, so even with a hot engine you won't burn yourself as your hands don't get near any hot exhaust parts. These plugs are the easiest plugs in the world to change, can be done in under ten minutes without even rushing.
 
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