I am a big car enthusiast who loves driving around in Volkswagens and Audis.
All but the most negligent of car owners keep up with the car-care basics: changing your oil, keeping your car clean, filling up with recommended gasoline. A clean, properly lubricated car is a happy car that keeps you happy (off the roadside and out of the garage) for tens of thousands of miles. If you want to step that up to hundreds of thousands – you'll have to step up your car-care game to higher levels of fastidious, but relatively easy maintenance.
Spark plugs are a critical and often-overlooked wear item. Responsible for igniting the air/fuel mix to start and run your car, these plugs can sustain sparks from 40,000 to 100,000 volts and see temperatures between 900 to 1,500 degrees Fahrenheit (about 500º to 800° Celsius).
Depending on the type of plugs in your car (copper, copper-platinum, or copper-iridium), some last longer than others – but all should be replaced after their recommended use.
This article covers:
- Spark Plug Basics
- Spark Plug Removal (using an Audi/Volkswagen 1.8T 20-valve engine as an example)
- Checking Your Plugs
- Spark Plug "Gap" Measuring and Adjustment (using NGK BKR7E plugs as an example)
- Spark Plug Installation
1. Spark Plug Basics
The opportunity for this article presented itself in the form of tune-up time for my 2000 Audi TT Quattro. NGK BKR7E plugs are a staple of 1.8T enthusiasts. To understand why we'll cover a bit of Spark Plug 101 (courtesy of NGK themselves).
In addition to materials in their core, spark plugs are also categorized by their "heat range": a measurement of their thermal efficiency. In plain English, by factors like the length of the plug's "insulator nose" (the white bit at the bottom of the plug), how far it extends from the threaded shell of the plug, and the core of the plug itself affect how "hot" the plug runs.
This is important because certain engines operate at different temperatures (oil temp, coolant temp, combustion temp) and not matching your plug accordingly can mean poor running.
- Too cold a plug won't burn the air/fuel mix efficiently, causing carbon-fouling.
- Too hot a plug risks burning the electrodes, warping the insulators, and potentially damaging the engine.
NGK Breaks Down Plug Heat Ranges
A plug's insulator design can have the greatest effect on its heat range. A fatter insulator (easily seen in the NGK-video at 1:01) means a colder plug.
NGK's BRK7Es are a good heat range for stock turbos, but tinkered 1.8Ts. Though nearly all plug cores contain copper for its superb conductivity, the 7Es are called "copper plugs" because they don't use platinum or iridium plating in their core, though the copper is still plated (fully-exposed copper would burn in minutes). Platinum and iridium in spark plugs increase longevity, at some cost to conducting efficiency.
Iridium and platinum plugs can go 40,000 to 50,000 miles easily, and cost more for that reason. The 7Es should be changed every 10,000 miles to be conservative, but provide a superb spark for my engine type (and are very easy on the wallet).
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2. Spark Plug Removal
This process will differ from engine to engine, but the gist will be the same:
- Access and remove the plug-wires (on older cars) or cylinder coil-packs (on newer cars like the TT)
- Change the spark plugs
- Reinstall your plug wires or coil packs
First, you'll want to let the car cool. A hot engine head can make over-tightening plugs easier (and burn you)!
You can pull the negative battery cable if you'd like, but my mechanics and I have swapped plugs and coil-packs without doing so – no issues.
Late-model cars likely involve getting plastic engine-covers out of the way (unless previous owners did away with them), but they typically pop-off or unscrew easily.
Spark plugs differ between engines (some using two per cylinder), but like most new inline fours, the 1.8T uses four plugs and a coil-pack for each.
- If you're using this as a step-by-step guide for a 1.8T plug service, you'll begin by getting the vacuum reservoir piggy-backing on cylinder 4 out of the way (10mm socket).
- Then you can take a 5mm hex-bolt key ...
- and begin unscrewing the bolts that hold the coil packs down.
TIP: Keep the bolts of your coil packs oriented the same way they were installed. It's a sure way to keep track of valuable bolts. Even though the bolts all have the same thread, years of use may have made individual holes "fond" of the small nuances from bolt to bolt. And I'm superstitious about anything that helps make reinstallation easier.
TIP: If you're looking at your 1.8T and don't see any bolts, don't worry. There was a design split between early and later 1.8Ts. Later models used in-house Audi/VW push-down coil packs instead of the older Japanese-made Hitachis. The screw-down Hitachis have a better reputation for longevity, though; screw-down conversions are available from suppliers like ECS Tuning).
- Once all the coil-pack bolts are removed, you can begin disconnecting the packs from the ignition harness.
TIP: Take care to notice the bracket the vacuum reservoir bolts onto – it's screwed on with both of cylinder 4's pack-bolts and one of cylinder 3's.
Depending on the age of your car, this next step can be a bit tedious.
- If your engine uses plug-wires leading to a distributor – this should be simple, pull the plug wires out carefully (they shouldn't fight you) and set them aside.
TIP: If your car uses a single distributor and plug wires, keep track of which wires go where! Out-of-order wires mean that the spark won't go to cylinders that need them at the right time (your engine may not fire up at all).
- If your engine uses coil packs, like the 1.8T, the plastic harness connectors can be brittle after being exposed to years of engine heat.
Depending on their condition, your harness connectors may still have the squeeze tabs that can be gripped (if you have G.I. JOE's handshake) or "coerced a bit" with an instrument like a flat-head screwdriver.
TIP: Take care when using a pick or screwdriver to squeeze the release tabs on the harness connectors! Old, heat-ridden plastic is touchier than a college student during an election year!
I've had the butt-puckering moment of having a bit of plastic bite the dust, but at least with this generation of Audi/VW connectors – it's not game over yet.
If you just damage the connector's clipping/releasing tabs, good news: this is a German-designed part. The guys that helped get us to the Moon. They think things through. Thank goodness, they knew some ham-fisted kid would be fiddling with it 13 years later, trying to keep his car going.
The insides of the connectors have rubber seals that provide most of the gripping action to the coil packs, and the squeeze-tabs were an (albeit frustrating) back-up. I hope the engineers of your car have your back the same way.
- With bolts and connectors out of the way, these screw-down coil packs come out with a gentle tug and a slight popping sound.
This is a good time to inspect the condition of your packs. A small white ring around their tips is normal. These coil packs have around 22,000 miles on them and were recently replaced after two of the 118,000-mile, 13-year-old originals finally bowed out.
Signs of a blown coil pack can include:
- a sudden kick (while driving)
- loss of power
- dim gauges and lights (fewer running cylinders means less alternator power)
- poor idling (like a popcorn maker, due to the uneven firing)
TIP: Like the bolts holding them down, I like to keep the coil packs in the order they were installed in. If for nothing else, this can help with future diagnosing of ignition issues: coil packs consistently blowing in one cylinder can indicate an issue at the engine-side or the wire-harness-side.
Now you're ready to pull the old plugs:
- You'll need a ratchet wrench, a 5/8th spark plug-socket (which uses a rubber-insert to grip plugs), socket extensions, and—a trick I picked up from my Mazda days—painter's tape.
- Take the socket extensions and wrap the tool where the socket and lower extensions meet.
This keeps your socket and extensions from coming apart when you give a premature tug to a plug that isn't fully unscrewed.
If your extensions and sockets don't grip well, they can split and force you to play the needle-nose pliers game (which sucks). A poor quality plug socket can cause this too if its rubber insert pops out easily.
With your plugs out, you can take advantage of a valuable opportunity:
- Check the condition of the used plugs. The condition of your plugs can indicate the condition of your engine.
3. Checking Your Plugs
- Too black and sooty? You're running rich or too-cold plugs.
- Oil-soaked plug tips? Some of your piston-rings or valve-guide-seals are highly worn.
- Does the plug tip look like you stuck it in a blender? The cylinder is "pre-igniting" (a.k.a.: "detonating," "pinging," or "knocking") or the plug is too long and contacts the piston.
Fortunately, these plug tips here look good, with an insulator that's still pretty white, and tan-to-grayish deposits on the electrode tips.
TIP: If you take plugs out and you see a reddish tint on the insulator and tip—don't panic just yet! Detergent additives in lower-grade (no name) gasolines, or octane boosters like Gold Eagle's 104 performance additive, can leave a red tint on the plugs.
If you're interested, Gold Eagle's 104 is a good store-bought octane booster that raised octane as much as three full points in magazine tests (91 to 94 for example). It also lacks MMT, an older octane remedy that works fine in regularly rebuilt race engines, but can damage street car parts like oxygen sensors and catalytic converters, and the environment.
If you like, you can keep track of which used plugs ran in which cylinders (this can help track engine condition).
NGK plugs come in individual boxes within the four-pack box, which can help you catalog used plugs.
The back of the box also has helpful suggestions for plug-torquing when installing the new units. Their suggestions are specific to the type of plug and type of engine head. It's a good idea to check your car manual or online resources in case your engine differs).
4. Measuring and Adjusting the Spark Plug Gap
Before installing the new plugs, it's a good idea to check their gap if your engine setup requires special adjustments. A spark plug's gap is the distance between its core electrode and its "ground electrode—between its tip and the curved arm beneath it. Adjusting this gap affects the nature of the spark it provides as well as its heat range.
For this, you'll need a gapping tool. There's several kinds, like the coin type I used, as well as feeler-blade and wire styles.
The latter two are considered more accurate by the elite, but I've used the coin type for several plug changes without issue. Use what makes you feel comfortable.
What is necessary with fine-wire plugs like the BKR7Es is a gentle, patient touch.
- When measuring with a coin-style tool, insert the thinnest side between the ground and core-tip first.
- Slowly move the tool along its increasing curvature until you meet with gentle resistance. The 7Es come pre-gapped to 0.35-inches. I know that in my case, a gap of 0.28-inches with this plug is ideal.
After all the talk of gentleness, this may sound strange: