For a while now I've had a miss on startup that clears within 10-20 seconds, which new leads hasn't sorted, so I figured/hoped a new set of plugs would sort that when I got around to it, or at worst one of my britpart coil packs was failing. This might still be an entirely unrelated problem, however..

Over the last couple of days I've had a missfire that rapidly got worse, to the point cyl 6 died entirely on my way home from work. Same on LPG and petrol. Plug lead connected fine at both ends, and it was only cyl 6 that was dead and not also a cylinder on the other bank, suggesting investigating the plug end first was the way to go. Pulled the plug... and it looked like this:

These plugs were new in 18 months ago, maybe slightly longer... so while they could do with changing, this looks concerning. I pulled another out and it looked like your typical wear - nothing unusual. #6 though looks like it has been rusting away...

I'm not losing coolant (for once), no steam other than when its humid out and the box has the usual condensation in it. Even if it were coolant, it wouldn't rust, and it should look clean rather than stained I would have thought. So lets say it was straight water in the cooling system, the plug would have to be sat in it to do that.

To further confuse things, when I did a compression test last year, this cylinder had higher compression than the rest - considerably higher if I recall. I didn't have my tester with me last night, just one that was older than me, which read about 150-180 psi but the non-return valve was leaking so didn't see a proper figure. I was mostly interested to see if I'd lost compression entirely at the time on that cylinder.

So I'm not sure what to make of this... conveniently had a spare plug from a Honda engined generator that fit, and its now running on all 8 again as if nothing had happened. Too early to tell on the startup miss, there seems to be little consistency as to when it does that, apart from cold startup.

But coolant in number 6? There's no coolant passages near the middle cylinders, only at each end of the heads so next to numbers 2 and 8. Unless it's getting in around the liner......

Balls accidentally deleted my other reply.

I've seen one place reference an orange colour as possibly being coolant in the cylinder.

But as you say... that only leaves a liner problem. If it is a liner problem, its impressively minor and one way, as I have no other symptoms. I guess time will tell on that theory. I plan to check the plug in a week or so if the problem doesn't return or escalate before then. If it does... I think I will have to SORN it and transfer my insurance to my BMW. This house malarky is expensive enough...

is it just me, or does it look pitted and rusty round the bottom of the thread?

Yes a coolant-getting-into-pot issue (eg. blown/iffy HG) usually gives that 'steam cleaned' look to the plug... Water quickly evaporates in the pot and does not usually produce such rust/corrosion either .. plus the plug thread also looks really quite nasty/rusty, too, also odd.

EDIT: As Aragorn just posted up, no it's not just you ! (and I agree with your comments below. too !)

Don't know how long you will be running your P38 but it would certainly be useful to check the 'new' plug in a week or two as you say.... assuming it does not clag up sooner than that.

When you say this pot gives a much higher reading doing the compression test how much higher ?
Normally if you have a 'path' though from pot to the water jacket it gives a low reading of course....

Could be a tiny liner leak but that would pressurise your coolant too...

when the hot engines shut off the coolant system is under pressure, and the cylinder isnt, so some water could leak up and into the cylinder.

That might explain rusty plug and the missfire on startup, and also the high compression test result on that cylinder...

Doesnt explain why theres no signs of compression getting into the coolant system though :/

The surround/bottom of threads is indeed rusty and pitted, that's what is weirdest to me.

Using it every day doing about 32 miles each day at the moment assuming I'm only going to work.

When I checked the compression last year, it was with the engine hot (that was fun), and I think it was over 200, whereas the rest were 170-180ish.

Well that compression reading is even stranger if the engine was hot... as it's unlikely that water in the pot could give a better seal/pressure reading... (unless it had turned to steam...).

How's the oil look, any emulsification ? Ph test on the coolant ? (Yes, both are tricky if it really is a tiny leak... at the moment..)
I may well get castigated/castrated for this but I start to think about Sodium Silicate-type resolutions if it is such a leak.

Any chance it could be a rogue plug with a manufacturing defect......................i.e.slightly incorrect mix of whatever metals they are made from.
Just a guess.

There have been cheap Chinese copy of NGK plugs reported and there's something about the base of that plug that doesn't look quite right. Apart from anything else it appears to say Made in France on it and it seems these aren't genuine NGK. See http://hyundaicoupeclub.co.uk/engine-wheels-brakes-suspension/where-find-genuine-ngk-spark-plugs-t24689.html

Dave w say,
How's the oil look, any emulsification ? Ph test on the coolant ? (Yes, both are tricky if it really is a tiny leak... at the moment..)
I may well get castigated/castrated for this but I start to think about Sodium Silicate-type resolutions if it is such a leak.

If you could see the rad I’ve just taken out of a 4.0 that had such stuff put in, you would avoid like the plague, it TOTALLY blocked the rad, no water flow what so ever..

Gilbertd wrote:

There have been cheap Chinese copy of NGK plugs reported and there's something about the base of that plug that doesn't look quite right. Apart from anything else it appears to say Made in France on it and it seems these aren't genuine NGK. See http://hyundaicoupeclub.co.uk/engine-wheels-brakes-suspension/where-find-genuine-ngk-spark-plugs-t24689.html

This gives better info on the fake plugs - scroll though to pics 15 onwards for the bits to look at on the plugs themselves, as you almost certainly don't have the packaging to check.
https://www.slideshare.net/athangal/distinguishing-fake-ngk-spark-plug

no10chris wrote:

Davew wrote: " I may well get castigated/castrated for this but I start to think about Sodium Silicate-type resolutions if it is such a leak. ">

If you could see the rad I’ve just taken out of a 4.0 that had such stuff put in, you would avoid like the plague, it TOTALLY blocked the rad, no water flow what so ever..

Should have explained better Chris... As stated I expected some 'backlash' but I meant Sodium Silicate only... Not the (expensive) stuff with 'additives' particularly those that resemble pancake mix that will block your Heater Matrix too. (Or even those 'gimicky' variants with tiny copper flakes etc) .

With tiny leaks Sodium Silicate can work... (with limitations), eg. http://catalog.miniscience.com/Catalog/Sodium_Silicate/Default.html

In this case there is no (apparent) loss of coolant, or coolant pressurisation effects etc of course, just the compression test anomally, but as also stated it could still be a tiny leak

That said I like the latest comments about NGK fakes (- although this would then likely show up on the other plugs too ?).

Not having a go Dave, whatever was put into the system I worked on was like a liquid silicone, never seen anything like it, I actually peeled a lot off the top of rad matrix, he did say it was ?????? Steel,, I must have a look at some point to add to not to buy list..

Didn't think you were 'having a go' Chris, just rightly saying "don't put cr@p in your coolant"! Think that chap was using 'Liquid Steel' (aka Snake Oil) ? It still surprises me too what folks will add to their rads - not just the proverbial raw egg - and then expect this to 'fix' it.... When it is the "Bars Leaks"/Pancake Mix-type stuff I usually tell them to expect to need to replace their rad (relatively easy) and/or the Heater Matrix ( usually a right PITA).

Sodium Silicate however is a powder - you dissolve it yourself - and has the advantage in that it becomes hard (as ceramic) only on contact with air+high temperatures: As stated it can certainly work on tiny leaks which is why folks try it with (small !) porous block problems.

Sodium Silicate is the leak sealing ingredient in Steel Seal and does work under certain circumstances, a slight weep around a liner would be one of those circumstances. It turns into a solid, almost like glass but stays as a liquid in the coolant so shouldn't clog a radiator or heater matrix. A small quantity is present in some brands of anti freeze even. Cheapest way of buying it is as a liquid like here https://www.ebay.co.uk/itm/500ml-Water-glass-Sodium-silicate-liquid-glass/140726670858 and you know that is all you are using and not Sodium Silicate with other additives to 'improve' it.

But, I'm more inclined to think along the lines of a dodgy plug.

Yes. I wondered if a (small !) liner leak could be cured with it too... In fact you can buy a whole kg of the power for about the same price (or in the US that bottle sells for about 3 times the price, but it does have an additive... yellow dye !.... )

It will be interesting to see just what Sloth finds when he looks at that plug again in a few hundred miles...

davew wrote:

no10chris wrote:

Davew wrote: " I may well get castigated/castrated for this but I start to think about Sodium Silicate-type resolutions if it is such a leak. ">

If you could see the rad I’ve just taken out of a 4.0 that had such stuff put in, you would avoid like the plague, it TOTALLY blocked the rad, no water flow what so ever..

Should have explained better Chris... As stated I expected some 'backlash' but I meant Sodium Silicate only... Not the (expensive) stuff with 'additives' particularly those that resemble pancake mix that will block your Heater Matrix too. (Or even those 'gimicky' variants with tiny copper flakes etc) .

With tiny leaks Sodium Silicate can work... (with limitations), eg. http://catalog.miniscience.com/Catalog/Sodium_Silicate/Default.html

In this case there is no (apparent) loss of coolant, or coolant pressurisation effects etc of course, just the compression test anomally, but as also stated it could still be a tiny leak

That said I like the latest comments about NGK fakes (- although this would then likely show up on the other plugs too ?).

Assuming the plugs all came from the same box etc of course - given they generally come in 10's it would be possible to end up with a single or couple of plugs from a different batch to the rest. (as you say you have a generator that uses the same plugs, so an odd number left in the box very possible) But the markings might help to tell on this. They appear to match as far as i can see, though of course its possible the fakers have upped their game somewhat.

My recent NGK plugs came in a plastic blister pack of four, rather than the usual cardboard box. I didnt even consider they could be fake... I should maybe pull one out and inspect the marks on the plugs themselves.

Interesting all round - so far things seem to be behaving. The plug I put in was actually some really cheapy - it was the right length and had the right thread, and was what I had to hand.

I'm pretty sure when I bought these they were the boxed individually type, though they were from eBay. The set as a whole are probably due for replacement, so I might get another set (from somewhere they should be genuine) and change them on the weekend. I'm hoping for the best outcome of a dodgy plug.

The oil looks fine, if not also in need of a change. I have a sniff testing kit for the coolant but annoyingly the fluid has turned so its no good.