Skip to Content

Are Bosch Spark Plugs Good? (Mechanics view)

Author: Qualified mechanic John Cunningham. Published: 2021/08/11 at 11:57 am.

I’m a mechanic, as was my father, and I’ve been using Bosch for as long as I can remember. I like their products, sure I’m sentimental but it’s deeper than that. I trust Bosch to perform, and that’s not something you just decide to do, trust develops with experience.

Bosch is at the leading edge of spark plug technology and has been for 115 years. They manufacture a range of spark plugs suitable for North American, European, and Asian vehicles. They use premium materials and cutting-edge design to stay one step ahead of the latest engine technology.

In this post, you’ll learn about Bosch spark plugs, why you can depend on them, and why it’s important to use quality spark plugs.

Why I Choose Bosch Spark Plugs

As you’re googling a question about spark plugs, I’ll take a wild guess and say you care a ton about your motor. I get that totally; I’m a gearhead and a mechanic.

But most gearheads don’t buy spark plugs every day. And a trip to the auto parts store can only serve to confuse. The choice is mind-numbing; all the plugs look pretty similar, and then there are the discounts to factor in. How do you even begin to know what brand spark plug you want?

Apart from the obvious factors such as proven reliability and performance, here’s what I look for in a spark plug:

  • Built from top quality materials, Platinum or Iridium
  • Anti-seize threads usually Nickle-plated
  • Pre gapped plugs (standard)
  • Long service life

Bosch has all these covered and some.

Bosch uses precious metals, platinum, and iridium in the manufacture of their plugs. They also use high-tech processes like continuous laser welding to ensure durability and reliability. Precious metals offer some significant advantages. They require less voltage to fire the plug and will tolerate much higher temperatures than a basic copper plug, and they resist wear.

I like that Bosch uses Nickle plating on the plug threads (a process developed in-house) to prevent corrosion, and corrosion is a common theme among other plug makers (more on how corroded plugs turn out later).

Bosch has always been at the leading edge of spark plug technology; in fact, they designed and patented the first reliable ignition system, a problem that was proving a tough nut to crack in the early days of auto development.

You could argue spark plugs look very similar now to how they did even fifty years ago, but looks are deceiving; plug technology has moved on quite a bit. And Bosch has been an innovator of much of it.

Bosch is a German brand, and although mechanics have been fitting them in European cars in North America for 110 years, it’s only in recent years technicians started fitting them to American and Japanese vehicles.

I’ve been using Bosch all my life; engines run smoother and quieter on their plugs. And both those qualities are usually present when an engine is running at its optimum. They make what I think are the finest spark plugs on the market.

Check out great deals on Bosch top-performance spark plugs here on

The Bosch Spark Plug Range

Evo Spark Plugs

The EVO is new and specially designed for the higher compression challenges of gas direct injection (GDI) turbocharged engines. It employs an Iridium firing pin and a platinum-iridium alloy for the ground disc. The precious metals promote reliability and longevity.

The plug uses an improved gas seal to prevent combustion leaks through the plug body and a stronger ceramic insulator, which is beneficial when fitting plugs in hard-to-reach knuckle skinning locations.

Double Iridium

The double Iridium is as good as spark plugs get. It sports a fine wire electrode iridium firing pin and a ground iridium disc. This plug is designed for durability; it will go the distance (about 100k) and perform flawlessly. It’s suitable for most modern vehicles.

Double Iridium Pin-to-Pin

The Double Pin to Pin is similar to the double iridium as per above. Employs an iridium fine wire electrode firing pin, and instead of an iridium ground, it’s replaced with an iridium pin, hence Pin to Pin. These plugs are designed with performance in mind, and so may not be suitable for all engines.


The entry iridium plug employs an iridium fine wire electrode firing pin and a standard ground electrode. It’s long life, pre-gapped as you would expect and is suitable for most if not all modern vehicles.

Double Platinum

The double Platinum is very similar to the double iridium, except you guessed it – it uses platinum instead of iridium. It sports a fine wire electrode platinum firing pin and a ground platinum disc. This plug is designed for durability; while it won’t last as long as the iridium, it will still cover the region of 60k without issue.


The entry platinum plug employs a copper core and platinum fine wire electrode firing pin with a yttrium-enhanced ground electrode. Yttrium ground enhances combustion. It’s long life, pre-gapped as you would expect and is suitable for most if not all modern vehicles.

Platinum Plus 4

A special plug indeed, and you’ll notice how different it is right off. Hey, it even looks fast! It employs a platinum central electrode with not one but four yttrium ground electrodes for maximum performance. Hence, it’s named Platinum + 4.

The plug’s special talent is getting up to temperature quickly and burning off those contaminates. For smoother starts, faster acceleration, and increased fuel economy, it may not be suitable for all engines.


The entry-level Bosch spark plug is not suited to all modern engines. It employs a copper core with a heavy-duty nickel centre electrode. It still performs a ton better than your basic copper core spark plug.

Silver Spark Plugs

The Silver is designed for your pre-90’s European vehicle where the combustion chamber temperatures are higher so it’s harder on plug electrodes. These guys are made tough; they employ silver alloy on the central electrode.

Mechanics tip

Replacing spark plugs for most vehicles isn’t too difficult, that said some larger engines require a ton of work to access the plugs. I’ve worked on some vehicles where I’ve had to remove valve covers and intake plenums to access the spark plugs. For modern large engines, that is not unusual.

If you go to this trouble to access the spark plugs, you can bet you don’t want to redo it again in 10,000 miles. You’ll fit the very best long-life plugs you can, Bosch Iridium, good for 100,000 miles.

No need to use anti-seize on Bosch plugs; the nickel plating prevents corrosion and galling

How Spark Plug Works

Spark plugs have a tough job. They partially live inside a combustion chamber where they must withstand pressure, chemicals, fire, and heat. And while under attack, they’re also a conduit for thousands of volts of electricity. It’s a pretty harsh environment.

Plugs need to do several jobs all at once:

  • Create a path for the coil to ground voltage
  • Seal the combustion chamber
  • Create an arc instantly and consistently

A plug’s main focus is, of course, to create a spark strong enough to ignite the fuel inside the combustion chamber.

The coil’s job is to produce voltage, and since the voltage will always seek the shortest path to ground, it races through the plug’s metal central core.

When the voltage arrives at the tip of the positive electrode, it’s faced with a gap and in order to make it to the ground, it’s forced to jump the gap; in so doing, it creates an arc (spark), and the magic begins.

But the plug is faced with some real challenges; heat is one of the main ones. The plug tip needs to get hot enough to burn off contaminants like oil, chemicals, and carbon that naturally collect around it inside the combustion chamber. But the electrode shouldn’t get so hot that it pre-ignites the fuel mixture.

It’s a balancing act – it doesn’t get hot enough, contaminates build up and causes it to misfire – Too hot, and we have preignition, and that can destroy an engine. A plug that performs reliably is super important.

Spark plugs vary in design and make-up. Plugs are specific to each engine, they are not universal and manufacturers test relentlessly to make sure their engines have a spark plug that’s the correct heat range.

Three plug types

Plug performance is relative to the metal materials used in their construction. Spark plugs are typically made from three types – Copper, Platinum, and Iridium.

Spark plugs are built tough; however, they are tougher than others.


Copper is a fantastic conductor of voltage; it’s a great choice for spark plug construction. However, it’s a soft metal, and heat causes it to wear out quickly. The copper core is a basic spark plug and is common in pre-1990s cars. In fact, many of these era cars will perform best using the basic copper core plug.


Platinum requires less voltage and will tolerate much higher temperatures than a basic copper plug. The higher heat tolerance allows the plug to burn off contaminants. Most vehicles from the 1990s onwards will happily run on platinum plugs. Platinum will last about twice as long as the basic copper core plug – about 60,000 miles.


Iridium spark plug costs the most but offers the greatest performance. Iridium allows for even greater heat without deterioration. As a result, Iridium plugs live the longest and are fitted to most high-end gas-powered engines. They typically last 100,000 miles. However, I’ve seen trucks with almost twice that and still no signs of failing.

Why Cheap Plugs Are Bad News

You already know cheap components are cheap for a good reason: they’re inferior. For some applications, like windshield wipers, buying cheap comes with very little risk. Spark plugs aren’t one of those types of components. When you’re fitting spark plugs, you want to fit the very best.

I’m a mechanic, and here’s what I’ve learned about cheap spark plugs in twenty-five years:

  • More likely to break inside the cylinder head
  • The treads corrode
  • Far more likely to misfire
  • Need regular attention
  • Poor for gas mileage and performance
  • Can be the root cause of other far more expensive component failure
  • Often the root cause of emission failures

Cheap spark plugs can end up costing you a ton of money. Three quite spendy problems include – Exhaust Catalysts, Ignition coils, and Cylinder head damage

Exhaust Catalysts The catalysts are as you know a critical component partly responsible for managing your car’s emissions. They are pretty tough bits of kit, but a few things can kill them, and raw gas is one of them. An engine that’s misfiring is pushing raw, unburnt gas into the exhaust system, where it collects in the catalysts.

Now, modern cars are smart enough to know when a plug or coil has stopped working, but if the misfire is intermittent, the ECU may not deactivate the fuel to that cylinder as designed. And that’s where you may end up replacing your spark plugs and your catalysts.

Ignition Coils – Ignition coils are pretty tough customers too, they can handle thousands of volts but they are designed to ground them out through the spark plug. A plug that refuses to fire or fires only intermittently puts a huge strain on the coil, and it may fail prematurely. Most modern vehicles employ a coil per cylinder, which is a good thing as the damage is limited to that coil alone, and a single coil is cheaper than a coil pack.

A third common problem with cheap plugs is corrosion; they generally don’t have very robust rust inhibitors. The metal threads corrode, and now you have a problem as they are stuck in the cylinder head pretty well. Some larger engines, as you know, will have a plug or two that’s a complete pig to access, and that’s when the job is going your way. A corroded plugin in that situation often means, believe it or not, cylinder head removal, and that’s a pretty big job.

I’ve found cheap plugs typically work fine at first, but as the going gets tough, they fail and usually intermittingly. Cheap plugs aren’t worth the risk.

How Much Should It Cost To Replace Bosch Spark Plugs?

The cost to replace spark plugs varies by the type of plugs recommended for your vehicle and how difficult it is to access your vehicle’s spark plugs.

Some larger engine engines, as said earlier are a total pig to access. Some will require valve cover removal and intake system removal. That’s time and extra cost for replacement gaskets, which can’t be reused. A seemingly trivial job turns into quite an expensive service.

Most, however, will have a four-banger engine, which means accessing the plugs is easy. And that’s what I’ll base this ballpark price on.

Fit four Iridium Spark Plugs

Plug cost $36 Labor $125

Fit four Platinum Spark Plugs

Plug cost $28 Labor $125

How Many Miles do Bosch Plugs Last?

How long Bosch spark plugs last depend largely on the type of materials used in the plug’s electrode. The electrode which lives in the centre of the plug carries the voltage (thousands of volts) needed to create the spark at the tip.

Bosch uses several different metals in their plugs – Copper, Nickel-Yttrium, Platinum, and Iridium. The electrode tip for example is crucial, the metal must conduct voltage easily but at the same time resist heat and erosion as the spark arcs. Bosch, therefore, uses the metal best suited to each hat the electrode wears.

  • Basic Bosch plug with copper electrode – typically last between 10,000 miles and 30,000 miles.
  • Bosch Platinum electrodes typically last about 60,000 miles.
  • Bosch Iridium electrodes typically last 100,000 miles.

How Often Should You Replace Bosch Spark Plugs?

How often you should replace your spark plugs is determined by a few factors.

  • The type spark plugs fitted
  • Your vehicles recommended service interval
  • The mileage covered
  • How old the plugs are

The type of spark plugs fitted – Copper plugs typically last between 10,000 miles and 30,000 miles. Platinum typically lasts about 60,000 miles, and Iridium lasts about 100,000 miles.

Your vehicle’s service interval – Manufacturers spend time and effort analyzing the optimum plug and service interval. Following the manufacturer’s guidelines, while obvious, is still great advice.

If you’ve ever considered becoming a mechanic, check out this post – Is it worth being a mechanic? And if you’ve ever wondered about rates of pay, you can check out job vacancies and rates of pay here on

You may find these posts useful:

Is it hard to change spark plugs?

Do spark plugs need to be torqued?