Spark plug change

[CatmanV2]

I'm rather surprised that we're looking at plugs with performance that deteriorates noticeably in 25k miles. Even by the manual they're not due for replacement until 31k.

C

 

[ratirati]

I didn't say the original plugs weren't working fine. But, I contacted my dealer about this and I'm going to replace them with the Denso's when he recommends, at 31k miles. My owner's manual also says 31k miles, or 50,000 kilometers.

 

[hodroyd]

Modern plugs are better I suppose, but 31K miles is a heck of a long time, that could be 10 years in some cases..!!

 

[rossyl]

What's to be gained from putting in new plugs?

 

[BennyD]

A lot if the old ones are; chipped, cracked, worn or misfiring. Iridiums are supposed to give a bigger spark which gives better combustion. At my last MOT, the unburnt hydrocarbons were showing 5ppm which I think is pretty good. She is certainly running well on Iridiums and has been for the last 15-20k miles on the same set.

 

[hodroyd]

The better the plug, in theory the longer they should last, I suppose I am a bit old school and think plugs should be checked and replaced a bit more regular, I might have to rethink..!!

 

[CatmanV2]

Modern plugs are better I suppose, but 31K miles is a heck of a long time, that could be 10 years in some cases..!!

I'm not sure how a plug (which is basically a piece of metal wrapped in ceramic) is going to deteriorate by aging over that kind of period, but I'm happy to be corrected.

The plugs in my Alfa GT 3.2 were due for replacement at 60k. I had them done early when the belts were being sorted as the rear bank is a it of a sod to get to.

C

 

[hodroyd]

Depends on the condition of the plug. You can get a carbon build up inside the plug if the engine has a slight burn issue, the spark then tracks on the carbon and can cause more issues, sometimes cracking the ceramic so the spark is not concentrated where it should be. I have seen old spark plugs that look like a knarled chunk of metal where the spark electrode should be and very little ceramic left to speak of. As I say, modern spark plugs are better at coping with the job, but do you take what someone else says as gospel, or do you like to actually check yourself..??

 

[CatmanV2]

Depends on the condition of the plug. You can get a carbon build up inside the plug if the engine has a slight burn issue, the spark then tracks on the carbon and can cause more issues, sometimes cracking the ceramic so the spark is not concentrated where it should be. I have seen old spark plugs that look like a knarled chunk of metal where the spark electrode should be and very little ceramic left to speak of. As I say, modern spark plugs are better at coping with the job, but do you take what someone else says as gospel, or do you like to actually check yourself..??

Oh sure, but that's only going to happen if it's used. So its still mileage dependent more than age, no? If the engine is just sitting there (which was my interpretation of you '31k could be 10 years' comment, the damage you describe won't happen. Or is there something else?

C

 

[hodroyd]

To some degree and I honestly don't think this would happen on our cars, there can be condensation build up sometimes within a plug, depends where it is parked for a long time. You can get some corrosion of the plug over time, but again depends on where and how the car is stored. If you found a car sat in a shed somewhere and it had been there 10 years, you bought it, would you change the plugs, oil etc, or just run it..??

 

[anotherdom]

Leave any metal you care to name in a non-inert environment and it will oxidise to a greater or lesser extent. Every time the spark fires there will be some erosion (evidenced by the requirement to re-gap plugs). Pulling plugs is also a very good way to check the mixture.

I don't like the current move to extended service intervals on plugs and fluids, and old oil is horrible stuff!

Treat the manufacturer service intervals as a minimum, particularly for a little used car I would suggest?

 

[CatmanV2]

To some degree and I honestly don't think this would happen on our cars, there can be condensation build up sometimes within a plug, depends where it is parked for a long time. You can get some corrosion of the plug over time, but again depends on where and how the car is stored. If you found a car sat in a shed somewhere and it had been there 10 years, you bought it, would you change the plugs, oil etc, or just run it..??

Fair call, Robert. I'd change them, but I'd not be too surprised if it ran just the same with the new or not plugs.

C

 

[hodroyd]

I agree, but old ceramics do start to craze a bit and any tiny crack would cause spark tracking, I would rather change them than hope they did not fail, but that's just me..!!

 

[CatmanV2]

Happy to accept that

C

 

[hodroyd]

Well thank you kind sir..!!

 

[Bart3200GT]

Cracking write up

 

[GS Geno]

Great write-up. Still helping 4 years later. Thank you.

Geno

 

[nfm]

Hi. Great thread here. My car has been off road over the winter to avoid the dreaded salt, other than the occasional start / warm up and run up and down the drive. When I took it out properly a week ago it was a tad off at 1st (for a few minutes only) and then ran fine. Likewise yesterday and I suspected just a bit of damp with maybe one cylinder not joining the party. Today it has continued to run rough and after a bit of R&D on here I have concluded, initially, that a plug may well be off. Mine were last changed five years / 20k ago. My thinking is it is a no loss strategy to change the plugs at this stage anyway, before going down the main dealer diagnostic road.

Could someone please confirm the latest thinking on the best plugs to buy, thanks. (Needless to say I am open to other diagnostic suggestions if anyone has any).

 

[highlander]

Easy stuff first. If plugs are 5 years old, I'd change them toot sweet

 

[BennyD]

My Iridiums have been in for three and a half years/ 30k miles and are still working perfectly. I've another set on standby awaiting the first misfire!