Is It Hard To Change Spark Plugs? (Mechanics advice)


DIY car repair is liberating, this stuff isn’t rocket science and you can absolutely do a ton of your own auto maintenance work. You’ll be amazed at what you can achieve with just some basic tools and a little know-how.

Changing spark plugs on most four-cylinder cars isn’t difficult. V6 and V8 engines may be more challenging as engine bay working spaces are tighter. In addition, the rear cylinders on both V-type engines are generally the most challenging of all, as they are tight against the chassis.

In this post, you’ll learn how difficult it is to change your car’s spark plugs. You’ll learn about the tools you’ll need and the process, I’ll also share some insider tips so you can nail it like a pro.

Assessing The Difficulty

Racing engine

Before beginning, you’ll need to have some idea of how difficult this is going to be, no sense in biting off more than you can chew. Most four-cylinder engines won’t be difficult to work on. Generally, there’s a ton of space under the hood. Larger engine performance cars or trucks are maybe a little more challenging. Engine bays have gotten smaller over the years while engine components are numerous.

Coil

Most modern cars will use a coil over plug (COP) set up, it simply means you’ll need to remove the coil before accessing the spark plug. The plugs themselves are usually berried deep inside the cylinder head and I’ll show you a trick for working on those later.

In addition to removing the COP, an intake Plenum may need to be removed, if this is the case, a new mating gasket should be replaced. Reusing the old gasket may cause a leak in the intake system, which in turn will lead to poor performance. Removing and refitting the Plenum isn’t difficult, but check the actual procedure for your make and model before attempting.

Plug Types

Plugs

Spark plugs come in various sizes and heat ranges but the two may type of spark plugs are long life and the standard plug. Long-life plugs are as their name suggests long life. The 14 mm Iridium long-life plug typically lasts about 100 thousand miles before needing to be replaced and is now fitted to most cars. They are of course more expensive than the standard type plug, costing between $10 – $20.

You don’t need to remove your plugs check which you have, the auto parts store will tell you or a good auto-parts website.  If your car is fitted with long-life plugs and you are not even close to the 100k, you can skip this maintenance chore.

Most plugs look similar, and they are but subtle differences to the seat mean we’ll treat them differently when it comes time to tighten them. The two types are the Washer (also known as a gasket) and the Tapered Plug. Identifying them is easy you’ll have no trouble.

The Washer spark plug has an attached gasket that helps seal the plug threads. When tightened the gasket crushes and deforms to the profile of the engine making a perfect seal.

The Tapered spark plug is, you guessed it, tapered. When tightened, the tapered area seals the threads against the cylinder head. The main point to note is the tapered plug requires less torque to tighten as it doesn’t have a crush washer.

Tools Needed

Spark plug fitting tools

The tools you’ll need will depend on whether you’ll need to remove the intake plenum or not. You can check out the tools I use here on the Mechanics tools page.

For most cars you’ll need the following:

  • Good quality 3/8 ratchet and socket set – Including a selection of plug sockets. Plug sockets are a little different from ordinary sockets, plug sockets bodies are slimline and employ an integrated hex head. Plug sockets also include a rubber grommet to help hold the plug inside the socket.
  • Booth puller pliers – The specialized rubber pliers is used for non COP setups where the plug wire fits the plug direct. The plug booths get a little tight and require the pliers to break them loose.
  • Anti-seize paste – The paste is used to help prevent galling, binding and seizing of the plug threads in the cylinder.
  • Fuel line – Used to help fit new plugs into awkward locations.
  • WD40 – Used to help free tight plugs.
  • Silicone lube – The lube is rubber friendly, repels moisture and helps make removal easy ant the next service interval.

How To Remove Plugs

Plug hole
  1. Remove the COP to access the the spark plug. You may need to disconnect the block connector.
  2. Using a suitable ratchet socket and long extension loosen the plug.
  3. Remove the ratchet when possible and continue to loosen by hand.

How To Fit The Plugs

Spark plug
  1. Prepare the the new plug by applying a small amount of anti-seize to the threads.
  2. Check the electrode gap.
  3. Don’t allow the plug slide down the plug hole, use the plug socket  holding feature or the fuel line hack.
  4. Start the plug on the threads by hand only, do not use the ratchet. Use fuel line to gain access to those awkward areas.
  5. After seating the plug by hand tighten the plug using a torque wrench or as per the info graphic below, note tapered is different to gasket spark plugs.
  6. Apply silicone lube to the COP boot or plug wire boot before fitting.
Spark plug tightening guide

Top Tips For Plug Replacing

Removing the plugs is as you now know not difficult, but it is possible to get things wrong. I’ve been a mechanic for more than twenty years and here are my tips for successful removal and fitting.

  • Cold engine – Only remove plugs when the engine is cold, helps reduce stripping threads.
  • Remove only one plug at a time – Removes the possibility of mixing up plug wires (if applicable).
  • Leave the new plugs in their box’s – Remove when ready to fit, prevents damaging the electrode.
  • Tight plugs – Open the plugs a half turn and spray WD40 into the plug hole, allow to soak overnight. Work the plugs a half turn alternately to free up threads.
  • Use 3/8 in Socket set – Using 1/2 inch socket set is too bulky and also applies excessive force.
  • Use fuel hose to fit awkward plugs – Allowing the plug to slide down the plug hole could close the electrode or damage threads.

What Can Go Wrong

Wd40 plug stuck

We don’t expect things to go wrong but we know they can, so here are a few of the more common minor disasters and solutions.

  • New plug falls on the ground and closes the electrode gap – Using a pliers bend the electrode back into position. Use a plug gap tool or improvise.
  • Job complete but engine misfiring – Check the plug wires are secure and in the correct order.
  • Stripped threads – Fit a Helicoil
  • Plugs binding – Carbon and corrosion causes the plugs to stick. Loosen just slightly to break their seal and soak in WD40 overnight. Working them back and forth gently usually does the job.

Related Questions

Why are the spark plugs so hard to get out? Modern cars use long-life spark plugs with a life span of 100 k miles. Often many years pass before the plugs are changed. The long interval promotes carbon and corrosion build-up. Open the spark plugs about 1/4 turn and spray liberally with WD40. Allow soaking overnight before working them left and right alternately until free.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty-five years, and I've worked for GM, Volvo, Volkswagen, Landrover, and Jaguar dealerships. My passion is cars. I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of car ownership, including buying advice, maintenance, and troubleshooting.

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