Question: I’m trying to change my own spark plugs for the first time and I’m a little lost. I’ve heard that I should wait until the engine is “cold” to change them, but I’ve also heard I should do it while it’s hot. I’m not sure which is true. Can I change my spark plugs while the engine is hot?
Answer: No, you should never change spark plugs while the engine is hot. Changing spark plugs on a hot engine risks damaging or stripping the threads in the spark plug receptacle or breaking the spark plug itself.
What temperature should my engine be when I change my spark plugs?
Your engine should be at an ambient “room” temperature when changing your spark plugs. This ensures the materials in the spark plugs and the materials in the cylinder heads will allow the threads in each to align.
If your engine is too cold when you change your spark plugs, you may not set your torque high enough, meaning your plugs will be too loose. This could lead to misfires and even engine damage.
On the other hand, if your engine is too hot, the plug threads in your piston head expand. Attempting to remove the existing spark plugs and install new ones in this state can damage the threads, and in severe cases, the entire head may need to be replaced.
Plus, we haven’t even mentioned the potential for burning yourself on a hot engine.
How to change your spark plugs
Once your engine is at the right temperature, Bosch, a manufacturer of spark plugs, recommends these steps for installing a new set of spark plugs:
- Disconnect the cables or ignition coils, and mark them to make sure you replace them in proper sequence.
- Loosen each plug one or two turns, then clean the surrounding area to keep dirt from getting into the threads or the combustion chamber.
- Remove the old spark plugs. If a spark plug is too tight, try to loosen it enough to add a drop of penetrating oil on the exposed thread. Screw the plug back in, and try again after a few minutes.
- Check the gap on the new spark plugs and adjust if needed.
- Thread in spark plug until hand tight, then use a torque wrench to tighten to the manufacturer’s specifications.
- Replace the spark plug wires or coil boots.
While Bosch recommends you use a torque wrench, they also provide an alternative method to tighten the spark plug without one:
- Hand tighten the spark plug until it is seated in the cylinder head.
- For spark Plugs with gaskets: tighten an additional 90˚(quarter turn).
- For spark plugs without tapered seats, tighten an additional 15˚.
Xuyun Zeng is a content strategist with a wide-ranging content background including tech, journalism, cars and health care. After graduating with highest honors in journalism, Xuyun led a newspaper to win eight awards, helped start an award-winning film industry podcast and has written over a hundred articles about cars repair, state laws and insurance. Prior to joining Jerry, Xuyun worked as a freelance SEO consultant with a mission to create the best content that will help readers and grow organic traffic.
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