spark plug replacement

Took delivery of my '03 C4 Cabriolet today. 33k miles. Oil/filter was just replaced. Pads/rotors done within last 2k miles. New battery (Dec. '14). I've read through the Porsche maintenance manual and found this: minor maintenance every 15k miles: replace pollen filter (done today) lots of "visual inspections - brake lines, other hoses, drive shafts, tires/spare wheel, vehicle lights, wipers, any warning lights -oil change all these things were just done during the PPI - the selling dealer changed the oil/filter and put in the new battery (wrong one as it happens an H6 whereas the manual calls for an H7) every two years: flush brake fluid Major maintenance every 30k miles: replace poly belt power steering - check level check tie rod ends, inspect pads/rotors every 60k miles: air filter fuel filter replace spark plugs (boxster/911) So here's my question: there is nothing about "age" vs. "mileage" re spark plugs. Should I change them? The RMS was done in '08 - at that time, they looked at the IMS and decided "no need to change it". I'm probably going to bring in the car for a brake fluid flush, have them "test" (if they can) the anti-freeze or if they can't, just replace it and probably replace the plugs. There is no (zero) sign of any oil streaks near where the RMS/IMS would be doing so. So I guess I'm not in a super rush to do an IMS replacement. Would you be? The clutch was also tested and the indie said: "no signs of slippage - clutch feels rock solid". So I'm thinking - drive it a while (perhaps up to a year), then have the drop the tranny and look at the clutch and do the IMS at that time.

Spark plugs fail because the electrodes eventually deteriorate (mileage dependent) or because they become fouled (which is not necessarily mileage dependent). Examine your coil packs. If THEY'RE shot - i.e. cracking - it's time to replace the packs and plugs.

Its always better to change the IMSB before any signs of it going south if you are going to change it at all. Your car is an 03 so it has the single row bearing in it, they are the the ones most likely to fail. I am not suggesting to change it or not to change, that is up to you.

Whether or not you have a warranty that covers that component and any related damage may also affect your decision. If it was my car, I'd put the "solution" in it and move on. Your car is much newer than mine with much lower mileage, so I'd want to take steps to ensure its longevity.

Regarding the spark plug replacement, my 2001 Boxster S service book states (just after the Major Service details list) to "replace spark plugs every 48,000 miles or 4 years whichever occurs first". I seem to remember some discussion as to why change plugs @ 4 years, which turned into who uses anti-seize on the spark plug threads....

You need to look again. There should be a section which gives services based on time and plugs should be in there. I frankly do not remember the rules for changing plugs on other cars I have owned but Porsche has a change schedule based on miles or time. Without going into too much detail when you change the plugs note the plug threads are discolored starting at the tip end and this extends the threads some distance. What happens is the pressure of combustion forces combustion gases into this space (tiny though it is). These engines run a lot of compression and combine this with the big power these engine make for their displacement the combustion pressures are quite high on top of the static compression pressure. These combustion gases and other combustion byproducts (water) form corrosive compounds. Over time these can damage the metal threads of the plug and if bad enough when the plug is removed the threads can damage the softer threads of the head. While of course new plug threads are easy to come by -- just buy a new box of plugs -- new threads in the head are harder to come by. In the plug and head combination the plugs are the sacrificial part. Better to discard relatively cheap spark plugs, albeit perhaps prematurely, in order to avoid possible head thread damage vs. running plugs too long and having to replace one or both heads if one can't salvage the damaged threads in the head. Note in the above I didn't mention anti-seize. However, I will if I'm pushed.

nudge...nudge...push...

I can't recall ever reading of an M96 spark plug being seized in the head, and I've probably done plugs in at least five of them in the last few years. Personally I wouldn't worry about it until 60k, because usually they still look pretty good at 60k. Btw, your 2003 no longer has a replaceable fuel filter. They went to an in-tank filter on the fuel pickup starting in 2002.

Back in September, I picked up a 2000 with 24k miles. The PPI recommended just doing a major maintenance since there was no indication of any of that work having been done during its life - and for me to establish a good maintenance baseline. Although the car ran fine, 4 out of 6 coils were cracked so we replaced all the coils and plugs (along with all of the other 60k stuff). The shop seemed to think they were the original plugs.... R

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Not everyone who has a problem with their Porsche comes here and posts. I have encountered a number of cars at various dealers in with serious problems and I can I believe count on the thumbs of both hands those who posted here about their cars. Thus for you to extrapolate that because you have not read of a problem in this area that one should ignore Porsche on this subject is a bit of a stretch. Furthermore, I have to point out that if anyone would know about this issue, regardless of where it occurs, it would be Porsche as it would get informed of this in or out of warranty. While some owners elect to use an indy many owners still have their cars serviced at the Porsche dealership. And I've been told -- and in a few cases observed this myself -- that while some owners who have their cars serviced at indy shop, still when something possibly serious comes up still prefer to have the work done at the dealer. One has to believe that Porsche -- like any other manufacturer -- bases its servicing schedules on real world feedback it gets over time from the number of cars that come in for servicing or that come in with problems. Given the desire to cut servicing costs that Porsche still has this requirement to change plugs on time says to me that it is a real concern to leave plugs in service too long. On matters like when to change plugs, all I can do is to point owners to what Porsche has to say about the matter. If the owner choses to ignore Porsche and let the plugs remain in service for a longer period of time than Porsche says they should be in service or run the plugs more miles than Porsche says they should be run, that is up to the owner. But I can't encourage it.

Macster is correct. Steel plugs in alloy cyl.head threads + moisture= corrosion.Lots of cars have this problem with extended service recdtns for plugs. Plugs are cheap,easy to replace,vital and give a visual indication of issues. Try dealing with one corroded plug and you will understand. When replacing ,use the minimum of anti seize on the threads and torque very ,very carefully& accurately.To find coil cracks ,you need to fastidiously clean them and inspect with a lens and bright light.

Macster has some wild theory on the plug threads that don't materialize in the real world. Long interval spark plugs threads are plates to resist corrosion. I've discussed this on other threads but he keeps bringing up the same of crap every time this topic comes up.

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Well, I am not aware of any long interval/long lasting plugs being approved for use Porsche engines. Since I use what Porsche recommends I change the plugs when Porsche says to. While long interval plug threads may have a treatment to resist corrosion -- something over and above nickel -- the resistance is not permanent. And maybe you need to read the fine print about long lasting plugs? Here's a snippet from Denso's web site: Q. How long will Iridium Last? A. Iridium use represents the most significant technological advance in automotive spark plug manufacturing, since platinum was introduced in the early eighties. As vehicle manufacturers produce increasingly complex and efficient automobiles, there is a greater need for long-life plugs that can tolerate leaner fuel mixtures and improved combustion processes. DENSO has responded to this need by developing its Iridium alloy, originally for OE applications. For example, many newer Lexus? and Toyota models carry an ultra long-life Iridium plug variation (.7mm with platinum tipped ground) that is capable of up to 120,000 miles of service. DENSO Iridium Power plugs, with their .4mm center electrode, have been developed for performance applications. Because gradual wear will ?round-off? firing points over time, the concentrated firing power and voltage requirement benefits will be reduced. For this reason, DENSO advises replacement after 30,000 miles. Based on the above, it appears if you want "long life" plugs you have to install in your Porsche engine the same plugs used in Toyotas. If you want a plug intended for use in high performance engine like your Porsche, you need to switch to the performance plug with a plug maker's advice to change the plug every 30,000 miles, which is fewer miles of service life than plugs Porsche specifies for these engines. How about another long lasting plug maker, like NGK? What does it have to say about when to change plugs: The best guide is the manufacturer's recommendation for your vehicle, as this particular service varies from brand to brand and model to model. Bosch doesn't list a replacement interval for its high peformance plug for my car. But the graphic for life span is not very comforting: http://www.boschsparkplugs.net/product.aspx?zpid=8113

Dude!! Spark plugs don't have a shelf life! They don't wear out from age. The plated threads will NOT cause corrosion to get them stuck in the heads either. If you had the first hand experience working on engines (that you seem to claim) you would know this. The wonder of the Internet nowadays is that if you look hard enough, you can find anything that will justify what you want.