Ask Oppo: Do coils wear out?

"NaturallyAspirated" (NaturallyAspirated) 08/07/2014 at 12:25 • Filed to: coils, ignition, Subaru

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I've been reading about people swapping the coil in their Subaru with the coil from a Neon R/T, since it supposedly gives a higher-voltage spark. Some of these people claim increased fuel efficiency, smoother idle, etc. Others report that they can't tell any difference at all. The suggestion is that those who noticed improvements had a worn-out coil to begin with, and that they would have noticed the same improvements if they had simply replaced their coil with a new OEM coil.

I can't seem to find much consensus on whether or not coils can "go bad;" some believe that as long as a coil still fires, it's fine, others think that they slowly wear out over time.

Can someone on Oppo explain this to me? Do coils wear out, and if so, what actually wears out?

crowmolly > NaturallyAspirated 08/07/2014 at 12:26

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I cannot explain in detail but from my experience YES, they can.

Jeremy H formerly Kalakaboooom > NaturallyAspirated 08/07/2014 at 12:28

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I don't know a whole lot about them when it comes to wearing out in the general sense, but about 6 months ago I replaced 3 coils in my wife's 300, because they were essentially burnt up. I guess the same thing happens to coils that happen to plugs, where they don't really "wear out", but they get burnt up.

Either way, not too sure on the semantics, but in my experience yeah they do need replacing eventually.

RazoE > NaturallyAspirated 08/07/2014 at 12:30

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I think so. I had 2JZ -GE VVTi coils on my 7MGTE, and they worked great (and looked much better)

Arch Duke Maxyenko, Shit Talk Extraordinaire > NaturallyAspirated 08/07/2014 at 12:36

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Like any electronic device, they go bad. Corrosion, burning out, etc...

Mattbob > NaturallyAspirated 08/07/2014 at 12:41

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The conditions in an engine bay are hard on interconnects and electronics. When you weaken connections and combine that with the high voltage in ignitions systems, you tend to get some arcing and oxidation which kind of snowballs things and wears them out. I imagine thats why you get some that just work for a long time, and some that take a shit.

jariten1781 > NaturallyAspirated 08/07/2014 at 12:42

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Not only can they go bad....but given enough time and temperature cycles all of them will go bad.

Insulation breaks down leading to arcing, wires/windings become more brittle leading to higher resistance or intermittent failures, corrosion can wear down contact points, etc.

deekster_caddy > NaturallyAspirated 08/07/2014 at 12:45

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In my experience coils are all-or-nothing. They don't "wear out" or "get tired" - they either work or they don't. Connectors and grounds get corroded and dirty though, so bad electrical connections can hamper a coil's ability to work properly.

camaroboy68ss > NaturallyAspirated 08/07/2014 at 13:23

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a coil can go bad, but its more like a bulb burning out. It works fine then it don't work no more.

JGrabowMSt > NaturallyAspirated 08/07/2014 at 13:23

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Yes, coils and their internals can burn up or stop sending signals to the plugs. Plug wires can also go bad over time.

When a coil pack goes bad, you will see all sorts of strange issues occur from CEL to hard starts, or other seemingly inconsistent trouble codes. The rough idle is really only the beginning.

Swapping coil packs can have repricussions though, as cars use specific parts for a reason. A hotter spark or more voltage can cause wear somewhere else, so In my experience, go for an aftermarket part with the correct ratings and more durability for a better experience over stock.

Just me though.

davedave1111 > NaturallyAspirated 08/07/2014 at 13:43

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Overheating is probably the most likely cause of coil failure, although insulator breakdown over time could also be a possibility. If I remember rightly, resistance increases as temperature rises (and high resistance increase temp), so once you get a small problem it would tend to get worse.