If you're burning oil, how black should a spark plug be?

that small an amount would probably not show up on the plugs. if it is the exhaust valve stem seals leaking, then the burning takes place in the exhaust, away from the plugs. easy way to check: remove the exhaust manifold and after leaving the car overnight look at the valve stems, you will probably see oil on the stems, same goes for the inlet

Reading through some recent posts and John Henderson posted this link:

Some knackered plugs in that lot. The slightly dodgy plug is 60% first picture and 40% the second. I was expecting more like picture three if it was burning oil.

Regards,

Tim

Exhaust manifold is simple enough, I'll probably have a look over the next couple of days. Inlet gets four spanners in Haynes and I've not had to perform before. Probably a weekend job for my first try.

My guess is to see the valve stem from the manifold, I would have to rotate the engine so the exhaust for the cylinder in question is down and leave overnight.

Regards,

Tim

Tim presented the following explanation :

Picture 3 is a really extreme case of burning oil, it is burning enough to foul the plug and completely loose that cylinder. Picture 1 I would suggest looks to me to be running a bit weak, I would expect a darker colour often described as 'tan' or a very pale brown - though it is difficult to tell from photographs.

I'm not able to see the pics but when my car was burning a lot of oil the plugs had a white/yellow almost ceramic coating. I guess it all depends on how hot the plugs run and whether the oil is stopping proper detonation.

Get someone to follow you in the car. Get it nice and hot. If the car puffs smoke on gear changes then chances are it could well be oil getting past the valve stems. If it leaves a cloudy haze all the time then chances are it's bore or piston ring related.

What car is it? When did you last change the oil?

Is the odd one at the same cylinder as where the oil looks to be seeping from????

adder1969 brought next idea :

I agree with that...

On tick over or even more so deceleration - your inlet manifold will be under maximum depression (vacuum) and any oil above the valve stem seals will be sucked in past the seals. Whereas under actual driving conditions on a part open throttle the vacuum is much less.

If there is bore or ring wear, then oil will be drawn into the cylinder all the time, hence it will produce smoke all the time.

Mine weren't black at all. They looked perfectly fine.

Thanks for the background information on why and what to look for. Typically I only look at the exhaust of my own car when starting from off and when ticking over. I'll bob out tomorrow night with the missus for a quick drive.

In another post, it was suggested that the cat would mask the symptoms once it was at operating temperature. Would this diagnostic test still work when the cat is at operating temp?

Regards,

Tim

Thanks for the info, I put a little more info in my follow on post to your reply.

Punto MKII with about 90K on it. I've been performing an oil change every 6-10k for the last 40K. Typically I put in GTX Magnatex purely on the principal that as it's the most expensive it's probably the best (plus snazzy adverts with CGI graphics and magnetic particle umph goes a long way when you don't know any better).

It was quite a shock to the system when I went to my local parts supplier and bought 5l of oil for £10. Kinda knew at that point the car was heading into retirement.

Regards,

Tim

This was the big surprise for me. I appear to have a little seaping oil from number 1 cylinder (timing belt end) head gasket. But the darker plug was number 4 cylinder. Maybe what I thought was seaping from the head is all from the cam cover gasket (new one is now installed).

Regards,

Tim

Out of all oils, I doubt magnatec is the most expensive or the best. Also it's magnAtec not magnEtec but yes the advertising does tend to suggest that it somehow sticks in some magic magnetic way.

Your oil loss could well just have been from the cam cover gasket.

He said magnAteX.

Does anyone know how/whether that's supposed to work?

I think he's pointing out that it's not magnetic, just a very similar but cunning play on words.

Thought I'd look into this on the corporate web site

and there it was... the snazy CGI graphics played out in full flash player glory. Anyway they have a "How it works section", which didn't turn out to be a petrol chemistry lesson but more along the lines of intelligent molecules.

Anyway the price has gone from £25 per 5l to £25 per 4l. Getting a bit pricey now.

Regards,

Tim

It's a mineral-base oil with some esters added. Motul makes some very good (but very expensive) full synthetic ester-based oils, and here's a fact sheet on their esters:

John

Interesting, thanks. Googling for "ester oil magnatec" reveals that a bloke on the internet reckons it has too litle ester in it to actually do anything useful. But what does he know.

As for the "intelligent molecule" stuff on Castrol's website that just seems to be setting the level of BS intentionally high to pre-empt anyone having issues with truth or facts.

But the polar molecule idea does make some sense.

Indeed, they're the only lubricants good enough for jet engines

- a much harsher enviroment than car engines though.

John