Replacing spark plugs is one of the easiest maintenance jobs on a car that almost anyone can do. However, it’s important to mention that spark plugs sit in a very sensitive and expensive part of the engine, the cylinder head. That’s why removing a stuck spark plug can be not only difficult but also expensive if not done properly.
If a spark plug won’t come out, it could be because of carbon buildup on the threads, corrosion, dirt, and debris on the threads, or the spark plug was cross threaded when it was installed. There are a couple of ways to get it out, with the most popular being soaking it with penetrating oil.
What Causes Spark Plug Won’t Come Out
Although it rarely happens that something goes wrong when replacing spark plugs, it’s not too surprising when it does. Spark plugs experience extreme heat since they sit inside the combustion chamber, plus they are sometimes exposed to weather, abrasive engine fluids, and contaminants.
There is also a slim chance that the spark plugs are stuck because of human error, so here are all the reasons why a spark plug seizes.
Carbon Build Up
Carbon buildup is something you will find in virtually every single engine on the road, especially inside the combustion chamber where the spark plug is located too. Now, if the spark plugs have done more than 50,000 miles and the engine has had issues with carbon buildup or the fuel system, the carbon can end up inside the spark plug threads.
Even though spark plug threads are extremely tight, the carbon is pushed into them with a lot of pressure. And given enough time and enough carbon buildup, the spark plugs can seize.
Corrosion
When the spark plugs are replaced regularly, there will almost never be any corrosion on them. However, if you have missed a couple of service schedules, corrosion can be a problem. Also, a lot of newer cars require iridium or platinum spark plugs that have much longer service intervals, so even with regular servicing, you might find corroded plugs.
Dirt and Debris
The spark plug location is usually buried deep inside the cylinder head and is a perfect spot for dirt to accumulate. Now, if whoever replaced them last wasn’t careful, some of that dirt might have ended up inside the spark plug threads. And since the threads have extremely low fitment tolerances, extremely tiniest debris can lock up the spark plug.
The Spark Plug Was Cross Threaded
On to another human error, cross threading. Cross threading is, in this case, when the male spark plug thread doesn’t line up with the female cylinder head thread but gets tightened anyway. When that happens, the threads on both ends will shave away, get stuck inside what’s left of the threads, and lock up the bolt/spark plug.
How Do You Remove a Stuck Spark Plug
There are a couple of ways you can remove a stuck spark plug, and it doesn’t hurt to try all of them if one doesn’t work. Also, don’t force the spark plug because you could snap it in half and land yourself in even more trouble. Not to mention that you could strip the cylinder head threads. So, here is how to loosen spark plugs.
Soak the Spark Plug in Penetrating Oil
If a spark plug won’t come out, using penetrating oil is the easiest way to remove it. For this method, you can use any type of penetrating oil, but the best penetrating oil for stuck spark plugs is probably WD40. But before you try to remove the spark plug, leave it soaked for at least 15 minutes. Then, try to remove it, and if it doesn’t budge, soak it again and leave it for the same amount of time. You can repeat this process as many times as you like, and make sure to apply the WD40 generously.
Then, if the spark plug breaks away, remove it. However, if it starts turning but has resistance, spray WD40 again and turn the spark plug patiently back and forth. Repeat that for as long as it’s needed, and again, don’t force it. Also, this is the only method of how to remove a stuck spark plug from an aluminum head without causing damage.
Try Heat
Using a blow torch on seized bolts is an ancient method still used and works just as well on spark plugs. However, spark plugs are often buried deep inside the cylinder head, so you have to be extra careful not to set something on fire or melt some wires or hoses.
Also, if you don’t have a blow torch, you can try heating up the engine to operating temperature. Although that’s nowhere near as efficient as a blow torch, that may as well be the final stroke for the spark plug to start turning. And as always, don’t force it. Move the spark plug back and forth until it backs out all the way.
On a side note, don’t heat the spark plug or attempt to remove the spark plugs when the engine is hot if your car has aluminum cylinder heads. Aluminum cylinder head threads are damaged much easier, and even under normal circumstances, the spark plug can rip them out.
Use Brute Force (Last Resort)
If all else fails, force is the only thing that remains to remove those stubborn spark plugs. Get yourself a big breaker bar; the bigger, the better, and have at it. The worst thing that can happen is you strip the cylinder head threads, not the best scenario, I know, but it’s fixable.
And with a bit of luck, the spark plug snaps in half, in which case you should get those easy-out extractors because they do wonders on broken spark plugs. But let’s not forget that neither of the two scenarios has to happen; the spark plug may just come out like it was never a problem. Still, if you are looking for a method of how to remove spark plugs without breaking them, this is not the one.
As for stripped cylinder head threads, sure, that can cost up to $1,000 sometimes, but the more realistic cost is around $200-$500. Moreover, you might just manage to fix it in your own backyard with a tool that doesn’t cost more than $40 on Amazon. To see what we mean, check out the video below, where you can see Scotty Kilmer use the tool and fix a cylinder head thread.
FAQs:
Q: Can I use WD40 to remove a stuck spark plug?
Yes, you can use WD40 to remove a stuck spark plug. WD40 is a penetrating oil designed for the exact purpose of removing stuck bolts, and it doesn’t hurt the engine if it ends up in the combustion chamber.
Q: What causes spark plugs to seize?
A couple of things cause spark plugs to seize. The first and most common is carbon buildup in the threads, which happens if the spark plugs are not replaced for a long time. Other causes include corrosion, dirt in the threads, and cross-threading.
Q: Is it better to remove spark plugs hot or cold?
It’s best to remove and install spark plugs when the engine is at Normal temperature, especially if it has an aluminum cylinder head. Removing spark plugs on a hot engine can damage the threads, and if they are installed in a hot engine, they can come loose. However, if spark plugs are stuck, and the engine has an iron cylinder head, you can try to remove them when the engine is hot.
Q: What tool is best for removing spark plugs?
The best tool for removing spark plugs is a simple spark plug socket that comes included in all socket wrench sets. The spark plug sockets are deeper than usual to accommodate the length of the spark plug; plus, they have rubber inserts that grip the spark plug and don’t allow it to fall out once it’s in.
Q: Can you drive with a seized spark plug?
Yes, you can drive with a seized spark plug as long as it’s tightened all the way. However, if the spark plug is seized but already backed out, that will lead to low compression and heavy misfires, both of which can damage the engine.
Q: What can I use for anti-seize on spark plugs?
You can use both copper and aluminum-based anti-size grease on your spark plugs. However, don’t cover the entire spark plug thread because it can lead to damage. Instead, put a small dot of anti-seize right in the middle of the spark plug thread.
Q: Should spark plugs be hard to remove?
No, spark plugs should not be hard to remove. Spark plugs will give significant resistance as you first try to unfasten them, but a normal-sized socket wrench lever should be enough. And as soon as they start moving, you should be able to remove them by hand.
Q: Can you spray PB Blaster in the spark plug hole?
Yes, you can spray PB Blaster in the spark plug hole because PB Blaster is nothing more than a penetrating oil made to unseize stubborn bolts. In other words, PB Blaster is the same as WD40, so it’s safe even if it gets into the engine.
Q: How tight should spark plugs be?
Spark plugs should always be tightened when the engine is Typical temperature and to the correct bolt torque using a torque wrench. But keep in mind that spark plug torque is different for every engine. And if you want to tighten the spark plugs without a torque wrench, use a standard-size socket wrench lever or ratchet, and stop when the spark plug gives too much resistance.
Final Words
In the end, regardless of what’s causing the spark plug to seize, be it carbon deposits, rust, cross-threading, or dirt, the removal methods remain the same. And those include soaking the spark plugs with WD40 or an equivalent penetrator and working the spark plugs slowly back and forth. That should be the first thing you try. If that doesn’t work, heating the spark plug with a blow torch or warming up the engine could help. And if all else fails, using sheer force is the only thing left to try.
