OK, but if you had less pointy central electrodes, the gap wouldn't open up as rapidly as the material would wear across a bigger cross-sectional area?  And the tip wouldn't be as fragile? Maybe?

The advantage of iridium plugs resides in the material itself, apparently it's so resistant that it allows the use of a fine electrode. Rather than an inherent design problem, I think the conditions inside the combustion chamber are so violent that the plugs couldn't have done any better, with the continued use of 95, 91 or lower octane fuels, they could only withstand that much. 

 

For reference, a new plug looks like this. 

40 minutes ago, Wino said:

I guess you mean pinking has caused the electrode erosion, rather than the other way round?

 

Yes. Absolutely.

16 minutes ago, juanse_2691 said:

it's so resistant that it allows the use of a fine electrode

When fuel quality is OK, I can see that working, but when poor?

That's the problem, these parts are engineered to perform under certain ideal conditions. The same happens to the engine itself, once its operating conditions deviate from the ideal, things start to go wrong and that's not the engine's builder's fault, conditions have to change to operate within range. No spark plug fares better in my experience, they only have to be changed more often, in fact it's usual here to change conventional sparkplugs every other oil change.

 

 

Since 95 is the best fuel I have available and using octane boosters is cost prohibitive, the only way I can see to ameliorate the symptoms is either lowering compression (moot point since the BBY has the same CR and runs fine on 95), using water-methanol injection (silly for a stock engine), or, most cost-effective, using a custom tune. I don't know if changing the thermal grade of the spark plugs would amount to something meaningful, but if it does, I'd gladly change them again at the next service. 

 

 

26 minutes ago, Wino said:

When fuel quality is OK, I can see that working, but when poor?

I don't really know. Iridium plugs are the heaviest duty plugs one as an ordinary man can get if I'm not mistaken, save for some sort of racing stuff. 

Is your cooling system performing OK? Just thinking that anything above normal 90°C operation isn't going to help things. Thermostat ever been changed? Rad fan(s) fully working?

I had to change the smaller fan on our Fabia a few weeks back.

Once I'd performed an autopsy on the old one, it was clear that only one out of the four brushes wasn't stuck, immobile in the holder.  It would start up sometimes, but often not, when the other fan did.

 

Edited 12 August, 20205 yr by Wino

1 minute ago, Wino said:

Is your cooling system performing OK? Just thinking that anything above normal 90°C operation isn't going to help things. Thermostat ever been changed? Rad fan(s) fully working?

I had to change the smaller fan on our Fabia a few weeks back.

Once I'd performed an autopsy on the old one, it was clear that only one out of the four brushes wasn't stuck, immobile in the holder.  It would start up sometimes, but often not, when the other fan did.

 

Thank you @Wino. My cooling system apparently works very well, I've never ever seen the needle going ever so slightly over 90°C even on traffic jams under the inclement tropical sun and AC on full blast, engine warms up fast, the one huge radiator fan works in its two speeds, there's no smaller fan present nor a suggestion that there should be one, which is weird, though I know there are different designs with one and two fans. Fan works without hiccups or worrying noises. Thermostat hasn't been changed to my knowledge, but it hasn't failed that I know. One thing I did change was the engine coolant temperature sensor but it was only ruling out fuel consumption problems. The new sensor didn't change things and the old wasn't faulty.

Also, this is the coil I replaced. Still the original unit apparently (33/06). There's another one like it so I'll change it as soon as I can, even though it hasn't failed yet.

I think big spark gaps cause the coilpacks to fail. I wouldn't change a working one, just carry a spare in the car and a means of reading fault codes (handheld scantool). 

My 2003 Polo has all four factory units still, I believe.

Great, thanks for the advice. I'll be a bit more zealous about the sparkplugs from now on. 

juanse, your English is so good. Are you Colombian?

2 minutes ago, TMB said:

juanse, your English is so good. Are you Colombian?

Hello @TMB and thanks for your kind words. Yes, I'm Colombian.

Just now, juanse_2691 said:

Hello @TMB and thanks for your kind words. Yes, I'm Colombian.

 

Hello 🙂 Very impressive 👍

Speaking of spark plugs, what's the consensus about spark plug temp range and gap? Would a colder sparkplug with a closer gap improve things, given that I have no say over the octane rating of the fuel? 

 

I have noticed that the BKR6EIX-11 have a gap of 1.1 mm which is huge, but since is what NGK recommended as an upgrade to the original plugs (BKUR6ET-10) I saw no problem with it. Would a BKR8EIX work better? 

 

Not to say I still have to check for carbon deposits and address the oil seepage through the valve stem seals.

It won't make any difference, the compression ratio is too high for the junk fuel you put in it, the ECU can't retard the ignition enough to stop the pinking.

@sepulchrave Thank you very much.