When to Replace Spark Plugs On Your Car

When to replace spark plugs on your used car: Spark plugs should be changed as general maintenance item or when your car develop problems with ignition system. Usually, spark plugs are first thing to be replaced when misfire trouble codes are present and engine is misfiring.

Replacing spark plugs is generally a straightforward job in 4 cylinder engines but it gets more complicated on 6 and 8 cylinder ones. However, still doable at home with few tools.

How Spark Plugs Work 

Spark plugs are used to create spark and ignite fuel in engine burning chamber. Gasoline engines have traditionally one spark plug per cylinder although there are designs with two spark plugs per cylinder, but these are a rare occurrence.

Spark plug is threaded into cylinder head and it extends inside cylinder burning chamber. Electrical current at very high voltage (30-40,000 volts) is supplied by ignition coil mounted on top of spark plug or distributed using spark plug wires. High voltage creates a spark inside cylinder chamber and ignites fuel/air mixture. How Spark Plugs Work.

Why Spark Plug Fail

Spark plugs will usually fail from extended use, failure to change them on time. Usually, worn spark plugs symptoms will manifest as single or multiple cylinder misfire. Check engine light and trouble codes will also be present.

Failed or failing spark plugs can make ignition coils fail too. As spark plug gets older gap between electrodes will get larger therefore creating higher resistance and requiring higher voltage to make a spark.

Ignition coils will have to work at their maximum capacity, this will cause overheating and premature ignition coil failure. A failed ignition coil might insinuate bad spark plugs.

Types of Spark Plugs

1) Cooper Spark Plugs  

This is the cheapest spark plug in the market. Its an old design used for low voltage systems and has a very good performance but a short lifespan. Cooper spark plugs have a cooper core with nickel based alloy electrode.

Conductivity of cooper is unmatched, well expect for silver that is. Cooper is the second most conductive metal after silver. High conductivity of cooper translates in higher performance when it comes to spark plugs.

Cooper spark plugs operate cooler than platinum or iridium counterparts and provide quite a bit of power. Copper spark plugs are commonly used on high compression ratios engines and turbo charged ones.

In any case, doesn’t make much sense to use cooper spark plugs for everyday driving, if platinum and iridium are available. Short operating lifespan of cooper spark plugs and frequent replacement are a hassle and an extra expense. Labor to replace spark plugs on some engines cost more than spark plugs.

While performance is very good, life expectancy is short as nickel alloy will be consumed by engine cylinder chamber high temperatures. Cooper spark plugs need to be replaced every 30,000 km or two years.

However, check your vehicle manual, if manufacturer recommends only cooper spark plugs for your engine and prohibits upgrading to iridium or platinum then use cooper spark plugs only.

2) Platinum Spark Plugs

These spark plugs are designed for longevity. Instead of using nickel based metals or cooper these design are made of platinum. Platinum is a hard metal with high heat tolerance (expensive metal too). Since platinum can handle heat very well, these spark plugs are designed to run hotter than cooper spark plugs.

Heat will burn deposits and keep electrodes clean while platinum electrodes will retain their properties for a long time. Platinum spark plugs are usually rated up to 100,000km or five years.

As conductivity of platinum is lower than cooper, performance will be lower too. However, platinum spark plugs compensate lower performance with a long lifespan.

3) Iridium Spark Plugs

Spark plugs are made with Iridium instead of Platinum. Iridium is harder than platinum and will tolerate even higher temperatures. It is also very dense, iridium is second densest material with Osmium being the first.

Iridium spark plugs are the most expensive, up to $30 per spark plug depending on spark plug model and type.

However, Iridium Spark Plugs make up for their high price with longevity. Iridium spark plugs are rated up to 150,000km with some manufacturers claiming up to 7 years and up to 200,000km lifespan.

Spark Plugs Price

Price is a bit subjective, as longevity should be considered too as part of total cost.

Cooper spark plugs: are the cheapest you can buy. However, while cooper spark plugs offer high performance and low price, on the other hand you will have to replace them 3 times more frequently than platinum or iridium ones. Low price of cooper spark plugs is negated when factoring labor costs and time to replace spark plugs every 30,000 km.

Platinum Spark plugs: Platinum spark plugs are a middle ground, more expensive that cooper and cheaper than iridium. These spark plugs offer higher operating life than cooper ones but shorter than iridium spark plugs.

Iridium Spark Plugs: Iridium ones are the most expensive you can buy but also have longest lifespan than cooper or platinum spark plugs. Iridium sparks plugs will save you some money on labor too. Due to their long operating life these spark plugs do not need to be replaced as frequently as cooper or platinum ones.

When to Replace Spark Plugs

Cooper spark plugs should be replaced every 30,000km or two years. As we said earlier, cooper elements doesn’t last long and spark plugs need frequent replacement intervals.

Change Platinum and/or Iridium spark plugs every 100,000 km to 150,000 km (or 5 years), with iridium spark plugs on higher range and platinum ones on lower range.

Regardless of what some manufacturer claim (10 years or 150,000miles, etc), its safer to change spark plugs at 100,000km and/or five years. Manufacturers testing is usually done on laboratories with optimal conditions and specifications. Every day driving is a different animal.

Do not wait for engine misfires to start, change spark plugs as maintenance item. You will get better fuel efficiency and engine performance when spark plugs are operating optimally.

A spark plug will require higher voltage to work properly as it gets older. Higher voltage requirements by failing spark plugs will shorten lifespan of ignition coils. Changing spark plugs is cheaper than changing spark plugs and coils.

Details on Spark Plug Construction by manufacturer Denso.

(If you are also looking for a fast and easy solution to sell your car, more here on “How To Sell Your Car Fast In Ontario” )

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