Spark plug replacement costs for a 2018 Jeep Grand Cherokee range from $150 to $300 at a shop, or $40 to $100 in parts if you do it yourself

The final cost depends on which engine you have, whether you go to a dealership or independent shop, and whether you handle the work yourself. A 2018 Grand Cherokee came with either a 3.6L V6 or a 5.7L V8, and the V8 costs more to service because it has eight spark plugs instead of six. Dealerships typically charge $200 to $300 total; independent shops run $150 to $250; DIY work costs mainly the spark plugs themselves, which run $8 to $15 per plug depending on the brand and heat range.

Most 2018 Grand Cherokees are due for spark plug replacement around 100,000 miles, though some owners report going longer without issues. Jeep's official recommendation is 100,000 miles for standard plugs. If you're approaching that mileage or noticing rough idle, hesitation on acceleration, or difficulty starting, a spark plug check is worth the cost of diagnosis.

Key Takeaways

  • A 2018 Grand Cherokee with the 3.6L V6 needs six spark plugs; the 5.7L V8 needs eight, making V8 replacement about 30 percent more expensive.
  • Dealership labor runs $100 to $150 per hour, while independent shops typically charge $75 to $100 per hour for the same work.
  • Spark plug replacement takes 30 minutes to two hours depending on engine type and shop efficiency, so labor cost varies widely.
  • OEM (Jeep factory) spark plugs cost more than aftermarket brands but often last longer and are what the engine was tuned for.

Dealership versus independent shop pricing

Jeep dealerships in most markets charge between $200 and $300 for a complete spark plug replacement on a 2018 Grand Cherokee. This includes both parts and labor. The dealership will use OEM Mopar spark plugs, which are engineered specifically for your engine and typically cost $12 to $18 per plug. Labor rates at dealerships average $120 to $150 per hour, and the job usually takes one to two hours depending on engine access and technician experience.

Independent repair shops and chain shops like Firestone, Midas, or local mechanics typically charge $150 to $250 total. They often use aftermarket plugs from brands like Bosch, Champion, or Denso, which cost $8 to $12 per plug and perform well in most cases. Labor rates at independent shops run $75 to $100 per hour. The lower total cost reflects both cheaper parts and lower labor rates, though you lose the may provide that comes with OEM parts and dealership work.

Some shops bundle spark plug replacement with other maintenance—air filter changes, fuel injector cleaning, or ignition coil inspection—which can raise the total bill but may catch other issues before they become expensive repairs.

Engine type and plug count affect total cost

The 2018 Grand Cherokee came with two engine options, and knowing which one you have is the first step in estimating cost. The 3.6L V6 is the base engine and uses six spark plugs. The 5.7L V8 is the performance option and uses eight spark plugs. This difference alone means the V8 costs roughly 30 percent more in parts and slightly longer in labor time.

For a V6 model at an independent shop, expect $150 to $200 total. At a dealership, expect $220 to $280. For a V8 model, independent shops typically charge $180 to $250, while dealerships run $260 to $320. These ranges assume standard spark plugs; premium or long-life plugs (which some shops recommend) add $3 to $8 per plug to the total.

You can find your engine size on the vehicle information label inside the driver's door jamb, or by looking at your maintenance records or original window sticker.

DIY replacement if you have mechanical confidence

Replacing spark plugs on a 2018 Grand Cherokee is a moderately difficult DIY job. The V6 is more accessible than the V8, and both are doable with basic tools: a spark plug socket, ratchet, extension, and gap tool. You'll need a new set of spark plugs ($40 to $100 depending on brand), and possibly a new set of ignition coils if the originals are worn (another $100 to $200 if needed).

The V6 typically takes 45 minutes to 1.5 hours if you work carefully and don't encounter stuck plugs. The V8 takes 1.5 to 2.5 hours because the rear plugs are harder to reach. The main risk is cross-threading a plug in the aluminum head, which requires a professional to repair and costs $200 to $400. If you're not confident with a ratchet and socket, the labor savings don't justify the risk.

Many independent shops will let you supply your own parts and charge only labor, which can cut your total cost to $75 to $150 if you buy plugs online. Ask the shop first—some have policies against customer-supplied parts.

When to replace spark plugs versus when to wait

Jeep recommends spark plug replacement at 100,000 miles for 2018 Grand Cherokees with standard plugs. If your vehicle has premium or iridium plugs (check your maintenance records), the interval may be longer—up to 120,000 miles. Waiting past the recommended interval risks rough idle, misfires, and reduced fuel economy, which can cost more in gas than you save by delaying the service.

Signs that replacement is overdue include hesitation during acceleration, difficulty starting in cold weather, a check engine light (especially codes P0300 to P0308, which indicate misfires), or visible carbon buildup on the plugs if you remove one. A single fouled plug can trigger a misfire code and cause the engine to run rough, but replacing all six or eight at once is standard practice because they wear together.

If you're buying a used 2018 Grand Cherokee and the service history is unclear, ask the seller when plugs were last replaced. If it's been more than 50,000 miles since the last service, budget for replacement soon after purchase.

OEM versus aftermarket spark plugs

OEM Mopar spark plugs are engineered for your specific engine and tuning. They typically last longer and are what Jeep recommends in the owner's manual. They cost $12 to $18 per plug at a dealership. Aftermarket brands like Bosch Platinum, Champion Iridium, or Denso Iridium are widely available at auto parts stores for $8 to $12 per plug and perform well in most driving conditions.

The difference in longevity is real but modest—OEM plugs may last 100,000 to 120,000 miles, while quality aftermarket plugs typically last 80,000 to 100,000 miles. For most owners, the cost savings of aftermarket plugs ($20 to $40 across a full set) outweigh the slightly shorter service life. If you plan to keep the vehicle past 150,000 miles or drive in severe conditions, OEM plugs are a safer choice.

Avoid the cheapest plugs at discount retailers—they often fail early and can cause misfires. Mid-range brands from established manufacturers (Bosch, Denso, NGK, Champion) offer the best balance of cost and reliability.

Additional costs that may come up during service

While replacing spark plugs, a technician may find issues that add to your bill. Ignition coils sit directly on top of the plugs and can fail around the same mileage—replacement costs $100 to $200 for one coil, or $600 to $1,200 for a full set of six or eight. If a coil is visibly cracked or corroded, replacing it during the plug service prevents a misfire later.

The air filter and cabin air filter are often checked during spark plug service. Replacing either costs $30 to $80 and is usually worth doing if they're dirty. Fuel injector cleaning is sometimes recommended and costs $100 to $200, but it's optional unless you're experiencing rough idle or poor fuel economy.

Some shops will recommend a compression test or fuel pressure test if the vehicle has a misfire code. These diagnostic tests cost $50 to $150 and can identify whether the problem is actually the spark plugs or something else—a worthwhile expense if you're uncertain about the cause.

Frequently Asked Questions

How do I know if my 2018 Grand Cherokee has a V6 or V8?

Check the vehicle information label on the inside of the driver's door jamb—it lists the engine displacement. You can also look at your maintenance records, insurance documents, or the original window sticker. The V6 is labeled 3.6L and the V8 is labeled 5.7L. If you're unsure, call a Jeep dealership with your VIN and they'll tell you in seconds.

Can I replace just one spark plug if only one is misfiring?

Technically yes, but it's not recommended. Spark plugs wear together, and replacing only one leaves five or seven older plugs that will fail soon after. Most shops require replacing the full set to avoid return visits and repeated labor charges. The cost difference between one plug and a full set is mainly the plugs themselves, not labor.

What's the difference between standard, platinum, and iridium spark plugs?

Standard copper plugs cost the least and last 30,000 to 50,000 miles. Platinum plugs cost more and last 80,000 to 100,000 miles. Iridium plugs are the most expensive and last 100,000 to 120,000 miles. For a 2018 Grand Cherokee, mid-range platinum or iridium plugs offer the best value unless you're doing DIY replacement and want to minimize future service visits.

Will replacing spark plugs improve my fuel economy?

If your plugs are fouled or worn, replacement can restore fuel economy to normal levels—sometimes improving it by 5 to 10 percent. If your plugs are in good condition, replacement won't improve economy. A misfire caused by bad plugs wastes fuel, so addressing it early pays for itself over time.

How long does spark plug replacement take at a shop?

Most shops schedule 1 to 2 hours for the job. The V6 is faster (45 minutes to 1.5 hours), and the V8 takes longer (1.5 to 2.5 hours) because the rear plugs are harder to access. If the shop finds additional issues like stuck plugs or corroded coils, the job can take longer and cost more.