Spark plugs... FWIW.

Just thought I'd share this. I had my car serviced last week. It's an '00 C2 with 79,000 km on it. Although it's a bit premature, my indie recommended changing the plugs, which he did. The result was transformational. The car idles more smoothly, tips in more naturally, and is turbine smooth even at low rpms. I emailed him about how markedly different the car runs, and this is what he said: "Since the major work, was to finish the service items, example the plugs, that is more than likely where the improvement was attained. Plugs are a consumable item, and they degrade in neutral or dynamic state, due to the nature of the environment at both extremes. In addition we service the electrical connections in the process of replacing the plugs, making absolutely sure the connection is solid. The new plugs are also torqued into place to assure a good seal, and sound structure, if a plug is too tight on the install, or slightly dropped prior to install, its reliability is questionable." Was interested to read that plugs can decay regardless of mileage, which is why I thought I'd post this. Just a sample of one, but I have to say that the difference was very noticeable for me. YMMV, obviously...

Porsche's maintenance guide says for MY00 Spark Plug Replacement: "911 Carrera (996) MY00 (Y) every 45,000 miles (72,000 km)" MY99 gets: "911 Carrera (996) up to and including MY99 (X) every 30,000 miles (48,000 km)" and MY01 and newer: "911 Carrera (996) as of MY01 (1) every 60,000 miles (96,000 km) or at least every 4 years"

I have never heard of any of the above?

*shrug* Hey, I'm not an expert, and I'm sure as hell not going to pretend to be one on a subject like this! (Other stuff, sure, but not this ). But this guy has impeccable Porsche credentials. Lifelong with the marque, a number of years as a crew chief with a prominent Porsche racing team. And it's a very reputable operation. All I know is the car ran noticeably better. For order of magnitude, think of it this way: the difference was more noticeable than when I did the Dinan chip on my last BMW.

Having worked in a garage during high school, I can tell you that the most common item performed in a "tune up" was changing of the spark plugs and sometime the wires. I often felt uncomfortable by how much the owner of the garage charged people for a "tune up", when all he was doing was oil, lube, plugs. If someone would have just requested these items, the bill would have been much less. It was a huge profit source for him, as it always had a dramatic change to the performance of most cars (these were daily drivers whose maintenance was usually ignored by their owners, so a plug change was usually long overdue). The owners never asked questions and were just happy that their cars ran better.

I dont understand the degradation at a "neutral or dynamic state" Also overtightening causing unreliability So I am giving a triple I am not claiming these are false claims, I just cant get my head around the theory. I am a pretty educated mechanic FWIW in cars/heavy equipment/airplanes. Thats why I want to know why.

My guess is that the gap on a spark plug is basically like any electrical connection. When it gets oxidized it is not as good (more resistance). The only thing that can happen when it sits (best I can tell) is that it gets oxidized. Even though it is not really a direct connection it does transfer electricity just like a connection. Just a thought....

Well, it's good to remember that just because people are good at doing something doesn't mean they're necessarily equally good at explaining it. Anyhow, car runs like a champ, and after owning more than two dozen of them in the last 31 years, I've become hard to please! (BTW, I'm pretty sure that aircraft mechanics use torque wrenches on spark plugs, no?)

Aircraft mechanics use torque wrenches on nearly everything along with safety wire and slippage marks for identifying issues on preflight inspections.

The minute it heats up from combustion it should rid the electrode and ground strap from any oxidation I would think? Torque specs for given category: Aviation-------torque wrench Cars-----------whatever the air ratchet puts out Heavy Equipment-------------whatever torque the 4-foot cheater pipe puts on the 3/4" drive breaker bar

Hasn't anyone dealt with a non starting mower, only to change the plug and walla ? Plugs degrade like most other things. After a while the spark is simply not as strong as when new - the why's are for someone else. I too just changed my plugs and have a smoother running vehicle.

Proper tightening torque is important for plugs for many reasons, including heat transfer to the cylinder head, so you get the correct heat range for which the plug is designed. Also, sparks, like lightning, prefer to jump off or to a surface at a sharp point or corner. The surface of the electrodes erodes/wears down over time. This causes it to require a higher voltage for the spark to jump off the surface.

Man, this thread is OUT THERE!!!!

Just make sure that you wrap aluminum foil around your wrists and ankles before you change the plugs. This will keep the "cosmic rays" generated by the spark plugs from getting to your gonads!

Now you tell me. Stupid forum...

So let me make sure I have this straight: We can carry on multi-page holy wars over oil viscosity, but saying "fresh plugs made my car run better" is 'out there'? I guess this would not be the time to bring up the whole 'earth is round' thing.

The way I took the explanation was that if spark plugs sat on a shelf unused, they would degrade, I guess I misinterpreted? Of course plugs will degrade with use and become unusable requiring changing.

I think what was meant was that your plugs deteriorate as much with time as with mileage. I can't say with confidence whether that's true or not for plugs, but I know it's true for lots of other things: fluids, seals, hoses, things like that. I've always personally believed that a low-use car needs as much or more attention as one that gets driven constantly.

Other than the outsides rusting, I can't believe plugs degrade with time.

What perhaps is true with the time/miles thing is that city miles are harder on them than highway miles (and typically cars with lots of highway miles do more miles in a given time period). I don't know, but I wouldn't be surprised if this were the case considering that the maintenance service manual for my 1985 Mercedes (back when MB was no holds bar only the best will do and these service manuals, unlike the CDs which are scans but somehow lacking, are a work of art) says to change the plugs every 30k for normal driving and 15k for hard driving.

Again, I think what he was saying is that they're still degrading even if the car is just sitting. It's worth understanding the guy's perspective on this stuff, too. His background is racing, where a tiny edge is still an edge. And their practice today includes a lot of vintage work. If you're working on a 328is that's been driven 2,000 km a year, you might have all kinds of cause to believe that plugs decay with time. For cars like ours that aren't 30 years old and get driven more, it's probably more academic, but I enjoy working with them anyway because they believe that everything counts. And, as I said, for my particular car and for whatever reason, I experienced a bigger improvement than I have in the past with stuff that cost me a lot more money...

How hard is it to change the plugs DIY style. And what plugs to use? How much does the dealer charge for just a plug change?

What he and Tippy said! oxidization.......... torque spec to help heat range............. a big electrical connection................. lightning jumping off surfaces I need to get back to my BAT CAVE.............

Funniest quote I have seen in a LONG time. JB

Is there a recommended spark plug for a 99 C4? Do any of our fine sponsors happen to sell them?

With one coil per plug and four electrodes it's hard to believe that the car is that sensitive to brand new plugs unless the old ones were fouled because of some malfuntion. But some guys can hear the difference of the wire feeding their speakers. Others can talk to the dead. ???? Flame Away....

Here's your flame. Nothing is impossible when you don't know what you're talking about.

Spark plugs are not worth it. I'm getting a diesel.

A surprising number of guys around here have never had their hands inside so much as a lawn mower engine, apparently. The idea that fresh plugs and wires can make an engine run better is infinitely more rational and supportable than some of the wild-*** speculation I've read on message boards about the magical healing powers of cold air intakes and how mufflers can improve throttle response and how there are dozens of free bolt-on horsepower available that Porsche was too stupid to find. I just thought it was a worthwhile experience to share with people who don't get to drive their cars a lot. I guess, for some folks, basic maintenance isn't expensive enough or doesn't provide any bench racing bragging rights. It's the only way I can explain the derision I'm getting.

Hey, I'm on your side of this discussion! I know plugs wear out and replacing them makes a motor run better.

Well if you don't think I know what I'm talking about that's your right. But I have been working on cars and building engines for them since I was 14 I'm now 66. I designed and built a capacitor discharge ignition system in 1961 long before they were in production cars. I have studied internal combustion engine theory extensively. I have a degree in EE. I understand the physics of how a spark propagates from one electrode to the other. Why spark plug gaps are now larger than they used to be. What heat range is all about etc etc. I could write a book about all of it but don't have the time or energy to discuss it all here.

OK. I'm an EE too, and I know a fair amount about the topic as well. I also know worn out plugs don't work as well as new ones. Period. Those multi-electrode plugs are there to hopefully get a spark across when fouled. They still work better when they're fresh. Bill

I knew that!

I had a �new remanufactured engine� install a few months ago. Since I now have a 2006 engine when do I need to change the plugs?

Spark Plug, Bosch Manufacturer: Bosch Spark Plug, Bosch Part # 14FGR6KQC is this a correct factory plug for a 99 c2 ? also is Saran Wrap not foil ok for my wrists ? i've used it in the past in other emergency situations with good results Thanks !

My best friend is an EGREGIOUS EGOCENTRIC...EE. I really don't like him

I knew that... was chiming in. But thanks!

So you have qualifications. What you don't have is critical listening skills. Nobody, least of all me, said that all cars will run better with fresh plugs. I said MINE did, and you have no knowledge of the condition of my car before the change. I then postulated that the same experience might be available to others whose cars were in similar condition. The only item under debate is, can plugs deteriorate for any other reason than mileage or fuel delivery problems? The guy I get my advice from says that, installed in an engine (as opposed to in a box on a shelf), they can. He makes cars go faster for a living. He also installed a CAI for me on the same day, but had the integrity to say that it was probably the fresh plugs that were making the biggest difference. Read my posts... it's all pretty clear. As a parting thought, you are probably well aware that the criticality of ignition specs in modern engines is far, far greater than it was when you were 14. (On my '67 Dart, I would gap plugs with a hammer and adjust mixture by ear and it would still run). But today I, for one, can't see the point of settling for 'good enough' when 'best possible' is so cheap. Same reason I buy premium fuel.