Spark plugs are changed every 20,000 to 30,000 km for nickel/copper ones, around 60,000 km for platinum and up to about 100,000 km for iridium, according to Caetano. The car's manual rules. Hard starting and misfires when accelerating are signs of worn plugs. Diesels have glow plugs.
This guide explains when to change spark plugs, which types exist, how to spot worn ones, what changes in a diesel car and what to ask for at the workshop.
When to change spark plugs
The short answer is: when the manufacturer says so. The interval is in the maintenance plan in the manual, and it varies with the engine and the type of plug. As a general guide, Caetano gives these figures:
- nickel/copper: change every 20,000 to 30,000 km;
- platinum: change around 60,000 km;
- iridium: can last up to 100,000 km.
The same source also advises checking the plugs every 20,000 km, to spot wear or deposits.
Types of spark plugs: copper, platinum or iridium
All of them do the same job, which is to produce the spark that ignites the mixture. They differ in the electrode material and, so, in how long they last:
- nickel/copper: the most common and cheapest, with lower durability;
- platinum: platinum-coated centre electrode, with better wear resistance;
- iridium: the highest-performance ones, with good heat and wear resistance;
- iridium/platinum: combine the advantages of both materials.
Always fit the type and part number the car maker specifies, because the plug has to suit the engine.
Signs of worn spark plugs
According to Caetano, the most common signs are:
- hard or slow starting;
- jerks or loss of power when accelerating, from misfires;
- rough idling;
- fuel consumption rising for no clear reason;
- the engine light on the dashboard, which may point to the plugs, among other faults.
The ACP adds another sign: when plugs are worn, leads damaged or coils faulty, fuel may burn unevenly, and the car «hiccups» (in Portuguese, «soluça»). In another text, the ACP notes that dirty plugs make starting harder and advises asking a workshop to check them.
These symptoms can also come from other faults, such as coils or injectors. So do not change plugs blindly: the engine light deserves a diagnosis. See what each symbol means in our guide to dashboard warning lights and other signs in the article on engine problems.
Diesel cars: glow plugs
A diesel engine has no spark: the mixture ignites by compression. The plugs it has are only for pre-heating, as Caetano says, which is why they are called glow plugs. Caetano gives no km interval for them, so check the manual.
According to a technical bulletin from Hella, faulty glow plugs show up as difficulty, or even impossibility, in starting the engine at low temperatures, heavy smoke after start-up and rough running. It is a typical winter problem, so it is worth checking them before the cold.
In used cars, the difference counts: among our active car adverts on 9 November 2026, 4,803 of 9,497 were diesel and 2,917 petrol.
If you buy a diesel, ask whether the glow plugs and the pre-heating system have been checked; if you buy a petrol, how many km ago the plugs were last changed. For diesels with a particulate filter, see also the guide to the particulate filter.
How much it costs to change spark plugs
There is no official price table. The price depends on the number of cylinders, the type of plug (copper, platinum or iridium) and the workshop's labour, and not even Caetano publishes figures: it points to a quote request. So ask for a written quote, with the plug part number, the price of each and labour shown separately.
If the engine has more cylinders, there are more plugs to change, and on some engines parts have to come off to reach them. Ask beforehand whether that is included.
Can I clean spark plugs instead of changing them?
Caetano says deposits can be cleaned with a wire brush and solvent, but that in many cases replacing is preferable to cleaning. If you change them, the gap between the electrodes must follow the manufacturer's specification, and the tightening must respect the recommended torque. If in doubt, leave it to a mechanic.
What to check when buying a used car
Ask for the service history and see whether a spark plug change is in the last service. On a high-mileage petrol with no record of a change, count on that cost. If the car starts badly when cold, idles roughly or has the engine light on, ask for a diagnosis before closing the deal.
You can compare adverts among the used cars for sale and get alerts for new adverts in the AUTO.MOTO app on your phone. If the cooling system is due a check, also read the article on coolant.
Frequently asked questions
When should I change spark plugs?
When the car's manual says so. As a guide, Caetano gives 20,000 to 30,000 km for nickel/copper plugs, about 60,000 km for platinum and up to 100,000 km for iridium.
What are the signs of worn spark plugs?
Hard starting, jerks or loss of power when accelerating, rough idling, rising consumption and the engine light on.
Do diesel cars have spark plugs?
No. They have glow plugs, which pre-heat the engine and make cold starting easier.
How much does it cost to change spark plugs?
There is no official table: it depends on the number of cylinders, the type of plug and the workshop. Ask for a written quote with plugs and labour itemised.
Can I clean spark plugs instead of changing them?
You can clean deposits with a wire brush and solvent, but according to Caetano, in many cases replacing is preferable.
