There is no single spark plug replacement interval that fits every car. Each manufacturer sets its own schedule in the owner’s manual, and that schedule depends on the engine, the plug type and how the car is driven. In a 2025 owner’s manual for a compact SUV, which includes a table for Canadian residents, one engine needs new plugs every 64,000 km (40,000 miles), while all other engines in the table need them every 120,000 km (75,000 miles). Your own manual is the only reliable reference for your model.
Why does the interval change from one engine to another?
Spark plugs create the electrical spark that ignites the air-fuel mixture in each cylinder. Every spark wears the electrode at the tip a little, and the gap between the electrodes gradually widens. How fast that happens depends on engine design, combustion temperature and pressure, and the electrode material of the plug itself. Two engines fitted to the same model can therefore wear plugs at different rates, which is why manufacturers publish different figures by engine rather than one number for the whole range.
How do I find my vehicle’s exact interval?
Start with the owner’s manual. The manufacturer’s online guidance says spark plug replacement guidelines vary by vehicle, and it directs owners to the ‘Capacities and Specifications’ section for the figure that applies to their model. Many manuals also include a separate maintenance table, so check three things before you rely on a number. First, identify your engine, since the table often lists a different interval for each engine. Second, look for the Canadian table if your manual has one, because it may differ from the table for other markets. Third, check the unit: tables often show kilometres and miles side by side, so use the figure that matches your odometer. Keep a note of the figure and the date and odometer reading of the last change in your service records.
A figure copied from a website or a forum is not a substitute for the manual. If the manual is missing, see the question at the end of this article.
When should spark plugs be replaced sooner?
The manufacturer lists five signs that plugs may need replacing before the scheduled interval, to avoid damage to the engine:
- the check engine light is on;
- the vehicle needs more fuel than normal;
- the engine idles roughly and is louder than usual;
- acceleration is slow;
- starting is difficult.
These symptoms can also come from other parts, such as ignition coils, the fuel system or sensors. They are therefore a reason to have the car diagnosed, not a reason to replace plugs by guesswork. A check engine light does not identify the faulty component, so have the stored fault codes read by a qualified technician before changing parts. If the light flashes, treat it as urgent: avoid hard acceleration and heavy loads, and have the vehicle inspected promptly, following the instructions in the owner’s manual.
Do severe driving conditions shorten the interval?
The manufacturer’s guidance consulted here does not give a general reduction for harsh use. Some owner’s manuals do include a separate maintenance schedule for severe conditions, such as frequent short trips, extreme heat or cold, towing, or dusty roads. In Canada, cold starts and repeated short trips in winter are the conditions most likely to match that description. Check whether your manual has such a schedule and, if your use fits its definition, follow the shorter figure. Do not borrow a number from another car or another market.
How do I replace spark plugs safely?
If you change the plugs yourself, work only on a cold engine, since exhaust and ignition components can be hot enough to burn. Follow the manual’s full procedure, including any steps for disconnecting the battery or removing ignition coils. Use the plug type listed for your engine, because the wrong heat range or thread can damage the engine. Tighten each plug to the torque value in the manual with a torque wrench rather than by feel, and avoid cross-threading the hole, which can require costly cylinder-head repair. Pull ignition coils straight out and avoid forcing them. Keep track of which coil or wire goes to which cylinder so the firing order is not disturbed. If any step is unclear, or if the car is not safe to drive after the work, have a qualified technician finish the job.
Frequently asked questions
Are spark plug intervals set by law in Canada?
The official sources consulted do not specify a government interval for spark plugs. The figure comes from the manufacturer’s documentation for each vehicle.
What if I no longer have the owner’s manual?
Manufacturers often publish digital copies on their websites. Have the vehicle identification number and model year ready, and confirm the figure with a dealer or qualified technician.
Can I check plug condition without removing them?
Not reliably. A visual inspection requires removing the plugs, so a technician will usually read the engine fault codes first.
