The question of when to change spark plugs on a car baffles many drivers and car owners.
Some say that spark plugs don’t need to be changed a long time while some are proponents of changing them more frequently.
The truth is that this dilemma is best solved with some prior knowledge on this topic. Both for keeping your engine in good running condition and to avoid throwing money away.
In this article, we’ll be talking about that and all the things you should know when it comes to changing the spark plugs.
WHY IS IT IMPORTANT TO CHANGE SPARK PLUGS?
The spark plugs provide a strong electric spark that ignites the air-fuel mixture in the combustion chamber of a gasoline engine.
This is a definition in a nutshell. If you have the time and will, click here for a more thorough definition from Wikipedia.
If the mixture is poorly ignited or not ignited at all, then the engine will not function properly or will not start.
About some of the symptoms that may happen in this case lower in the article.
So, if you want the engine running at one hundred percent efficiency, the spark plugs must be in prime condition.
HOW OFTEN TO CHANGE SPARK PLUGS?
The interval for replacing spark plugs highly depends on the material and quality they’re made out of. This is a crucial factor.
The basic types are:
Regular copper spark plugs
These have a solid copper core with a nickel alloy electrode. These types are mostly used in older car models and ones with ignition systems that have a lower voltage. Consider this the old-school spark plug that is slowly going out of use.
Long-life spark plugs (iridium or platinum-tipped)
These spark plugs are present in almost all modern cars as they are made for modern ignition systems and have a much longer service life due to using precious metals on the electrodes.
They may also have more than one electrode on them.
Due to using precious metals and because they have a long service life, they are usually several times more expensive.
Having this in mind the proper maintenance interval would be:
Regular spark plugs
From 15.000 to 30.000 kilometers (approximately 10.000 to 20.000 miles).
Quality is a key factor here.
For instance, if you buy low-quality spark plugs you should expect to change them at 15.000 kilometers (if they last that long). If you buy quality ones from renowned manufacturers they may last well beyond the 30,000-kilometer mark.
Long-life spark plugs
From 60.000 kilometers up to even 200.000 kilometers (approximately 40.000 to 100.000 miles)!
The average service interval is 100.000 kilometers or 60.000 miles.
It must be said that the 200.000 kilometers is possible but the spark plugs have to be of premium quality. The engine also has to be in top condition as well as the ignition system.
It’s rare to get to this point since a regular maintenance interval (and common sense) demand replacement well before this.
Regardless of the type of spark plugs on your engine, be sure to use ones that the car manufacturer recommends, especially regarding the correct specifications.
If you visit a mechanic or service, they will know for sure.
If you’re going to do a DIY replacement you can find the exact specifications in the user manual, ask at the car parts shop, or just Google it.
This is very important as replacing ones with the wrong specifications (although they look the same) can cause problems like improper engine functioning, higher fuel consumption, the spark plugs will not last as long as they should, etc.
WHEN TO CHANGE SPARK PLUGS? COMMON SYMPTOMS
1. ROUGH IDLE
This is probably the first and most obvious symptom.
What you’ll feel first is a periodical rough idle, maybe only a second or two, and perhaps only in the morning while the engine is cold.
As the problem gets worse, the idling will be rough all the time, even when the engine has reached working temperature.
Regarding when to change spark plugs, once this symptom appears, check immediately when they were changed the last time.
2. SLOW ACCELERATION
After the occasional rough idling, you might feel a change on the gas pedal.
The acceleration will first slightly decrease only to get worse as the spark plug problem progresses.
3. HIGH FUEL CONSUMPTION
Spark plug problems have a huge impact on fuel consumption (for more information on the fuel consumption topic, click here).
As with the previous symptoms, as the problems get worse, so will the fuel consumption get higher.
An increase as large as 50 percent is expected if the spark plugs are really in bad condition.
4. ENGINE MISFIRING
Engine misfires usually appear in the last stages of the problem.
This happens when the spark plugs have a weak spark that can still ignite the air-fuel mixture but not sufficiently.
You’ll first notice slight interruptions in the normal sound of the engine. If the misfire continues unchecked, banging and thumping may replace the usual engine sound.
In more severe cases, you may even get loud banging noises coming from the exhaust pipe.
Also, instead of the engine firmly laying in the engine bay, it will violently jolt and jump from one side to the other.
5. CHECK ENGINE LIGHT
The check engine light will come up for sure, if not while rough idling then when misfires appear.
Sometimes the spark plugs will not be the cause of the check engine light but rather the O2 sensor.
Since the combustion is irregular (and the exhaust fumes also) this will trigger the O2 sensor.
For more information on the O2 sensor problem, click here for a separate article on that topic.
6. CAR WON’T START
At the final phase of the problem, where the spark plugs totally malfunction (several of them) the car won’t start at all.
It’s can be preceded by some severe engine misfire.
The engine will probably give signs of wanting to start (cranking and almost starting) but won’t be able to.
Keeping track of when to change the spark plugs will save you from this worst phase for sure.
HOW MUCH DOES A SPARK PLUG REPLACEMENT COST?
The cost of replacing the spark plugs depends on a few factors:
Engine type, namely the number of cylinders
More cylinders=more spark plugs=more labor=more cost.
Type and quality of spark plugs
The regular, copper ones are cheaper while the long-lasting iridium or platinum ones are usually much more expensive.
Quality has a major role in the price: renowned quality manufacturers are pricey but guarantee for longevity.
Accessibility of the spark plugs
Since most modern engine bays are cramped, additional dismantling to reach the spark plugs is almost inevitable on a lot of cars.
Also, on modern engines, the ignition coils have to be disconnected and removed.
All of this means more or much more labor money on the repair bill.
To conclude on this part:
Prices for quality spark plugs start from about 6 US dollars and go up to about 12 US dollars or even more. The price is per one piece.
The price of labor highly depends but for a smaller four-cylinder engine and if the spark plugs are accessible, a good price is 40 to 50 US dollars. For bigger engines and more premium cars, it may go up to 200 US dollars for the whole job.
The end sum for a spark plug replacement ranges from about 70 US dollars to 250 US dollars or more.
The key factor for avoiding any kind of spark plug problem is regular maintenance.
Timely visits to a good and trustworthy mechanic will guarantee that the spark plugs will be changed on time.
If you’re DIY oriented and have the will, means, and tools, you can change or clean the spark plugs yourself. A DIY option is especially good for cleaning the spark plug and checking the electrode gap. Doing this once in a shorter service interval or twice in the longer interval should be enough.
Also, this is good for warning on time if there is some kind of engine problem (lean mixture, rich mixture, engine burning oil, etc).
Furthermore, I must emphasize the need to buy quality spark plugs and from trusted manufacturers. Again, some more money, in the beginning, means less later. Fewer problems also.
Knowing when to change spark plugs, reacting on time if a problem occurs, and using quality parts is a key factor for the longevity and quality functioning of the engine.
Written by: Sibin Spasojevic
Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com