You’ve noticed your car acting a bit off lately - it’s shaking when idling at red lights, the engine stutters, and your gas mileage has tanked.

Chances are, your spark plugs are shot—and the longer you wait, the more serious (and costly) damage you’ll do. 

The good news? A Spark plug replacement cost is nothing compared to a misfire that ruins your ignition coils or clogs your catalytic converter.

Let’s tackle what a spark plug is, signs it’s time for new ones, and how to get them replaced properly at the right cost.

What is a Spark Plug

A spark plug may be small, but it plays a huge role in how your car runs. When you turn the key or press the start button, your spark plugs ignite the air-fuel mixture inside your engine and keep the combustion cycle going.

No spark? No start. That’s how important these plugs are. 

Over time, they wear out. And when they do, your engine will start to stutter, burn more fuel, and misfire or stall out altogether.

Types of Spark Plugs

Not all spark plugs are the same—and the one your car needs depends on its engine design, age, and how you drive. Check your owner's manual or ask a trusted technician before you buy. 

Here's a quick breakdown of the most common types:

• Copper Spark Plugs

These are the most affordable option, but they wear out quickly—usually lasting around 20,000 to 30,000 miles. They’re best for older vehicles that don’t require high-performance parts.

• Platinum Spark Plugs

Platinum plugs last longer than copper—up to 60,000 miles—and provide better performance and fuel efficiency. They're a solid mid-range option for many modern vehicles.

• Double Platinum Spark Plugs

These offer even better longevity and are often used in waste spark ignition systems, where both plugs fire in the same cycle. They can last up to 100,000 miles.

• Iridium Spark Plugs

Iridium plugs are the most durable and efficient, designed for newer, high-performance engines. Though more expensive, they often last 100,000 miles or more and deliver top-tier performance.

What Happens If Spark Plugs Fail?

When you have faulty spark plugs, your engine doesn’t run like it should—and sometimes, it won’t run at all. These small parts keep your engine firing smoothly. When they go bad, everything from performance to fuel economy starts to drop.

You’ll notice rough idling, misfires, slow acceleration, or poor gas mileage. If the issue goes unchecked, it leads to damaged ignition coils, clogged catalytic converters, or hard starts in cold weather.

Replacing worn plugs is preventative care that saves you from much bigger problems.

5 Signs Your Spark Plugs Need Replacing

Spark plugs don’t last forever—and your car has a way of letting you know when it’s time to swap them out. Here’s what to watch for:

#1. Your engine misfires or runs rough.

A bad spark plug disrupts the combustion cycle, leading to shaking, hesitation, or jerky acceleration.

#2. You’re burning through more gas than usual.

Worn plugs make your engine work harder, which means lower fuel efficiency and more stops at the pump.

#3. The engine is hard to start.

If your car cranks too long before starting—or won’t start at all—it could be a failing spark plug.

#4. You notice slow or sluggish acceleration.

A healthy engine should respond quickly. If yours feels sluggish, bad plugs are likely the culprit. 

#5. The check engine light comes on.

Modern engines will detect misfires or poor combustion caused by faulty plugs and trigger a warning light.

Spark Plug Cost Guide

Several factors influence how much you’ll pay, from parts to labor to engine design. Here's what really drives the total spark plug replacement cost:

Type of Plugs

The material makes a big difference. Better materials mean higher upfront costs, but fewer replacements over time.

• Copper plugs are the cheapest, but wear out fast—expect $2 to $5 each.
• Platinum plugs usually run $6 to $10 each and last much longer.
• Iridium plugs, built for performance and longevity, can cost $15 to $25 per plug.

Labor Charges

Labor costs vary based on your vehicle and where you live. High-performance or compact engines often take longer, which raises the labor rate.

• For easy-access engines, labor ranges between $40 and $80.
• On engines that require removing other components to reach the plugs, labor climbs to $150+.

Number of Cylinders in the Engine

More cylinders mean more plugs—and more cost. Multiply your part and labor costs by the number of cylinders to get a more accurate total.

• A 4-cylinder engine needs four plugs.
• A 6-cylinder engine needs six.
• An 8-cylinder engine? You guessed it—eight plugs to replace.

Auto Repair Shop vs. Dealership Pricing

Independent auto repair shops, like Milex Complete Auto Care - Mr. Transmission Columbus, offer better rates than dealerships. Don’t forget to ask what’s included—some shops will also inspect coils or run diagnostics during the service.

• Shops charge between $100 and $250 total, depending on labor and parts.
• Dealerships run between $200 and $400, especially for performance models or imports.

Risks of Improper Spark Plug Installation

Installing spark plugs incorrectly causes real damage—not just to the plugs, but to your engine. It’s more than just screwing them in. Here’s what can go wrong:

• Cross-threading the plug strips the cylinder head.

When you don’t line up the threads properly, you can tear into the cylinder head. This often leads to costly repairs or full replacement of the part.

• Over-tightening cracks the plug or damages the cylinder.

If you apply too much force, you can break the ceramic or crack the engine’s cylinder head—both lead to misfires and serious engine issues.

• Under-tightening causes poor contact and misfiring.

A loose plug won’t sit right, which prevents proper firing. That makes your engine stumble, idle rough, or burn fuel inefficiently.

• Using the wrong plug throws off your engine’s performance.

When you install the wrong type, size, or heat range, your engine may knock, misfire, or wear down faster over time.

Spark Plug Replacement Cost: Frequently Asked Questions

How much should it cost to change spark plugs?

Spark plug replacement typically costs between $100 and $250+ for a standard vehicle. This includes both parts and labor. The final cost depends on the type of spark plugs used, the number of cylinders, and how difficult it is to access the plugs in your engine. High-performance or imported vehicles cost more.

What are the signs of bad spark plugs?

Common signs of bad spark plugs include engine misfires, rough idling, slow acceleration, reduced fuel efficiency, hard starts, and sometimes a check engine light. These symptoms happen because the spark plugs can no longer ignite the fuel-air mixture effectively.

Why is a spark plug change so expensive?

Spark plug replacement gets expensive when your engine design makes the plugs hard to reach. Some vehicles require removing intake manifolds or engine covers, which increases labor time. Using premium spark plugs, like iridium or double platinum, also raises the total cost.

Can I drive my car with bad spark plugs?

You can drive with bad spark plugs—but you shouldn’t for long. Failing plugs reduce engine performance, cause misfires, and strain other parts like ignition coils and the catalytic converter. Driving too long like this can lead to bigger and more expensive repairs.

Get a Smoother Ride with Milex Complete Auto Care - Mr. Transmission Columbus

If your engine is running rough or your mileage is dropping, don’t wait until you're stuck on the side of the road. At Milex Complete Auto Care – Mr. Transmission Columbus, we replace spark plugs the right way—with quality parts, expert service, and zero guesswork.

We’ll inspect your system, explain what’s happening, and get you back on the road fast. No upsells. No surprises. Just honest work from people who know cars. Book your spark plug service today and keep your engine firing strong.