Deposits on spark plugs - causes?

[dhutch]

Just had the plugs changed on my E46 330ci M54 engine, photos below show a sample of those removed.

There is very little 'wear' or erosion of the electrodes, which is not to surprising for a long life plug. However there are significant deposits and I wondered what if anything the causes for this might be and how much of a concern or indication of anything it is.

My understanding is this is not a major issue and could be normal, but could also be made worse by worn valve seals.

Obviously in part, this is why you replace them from time to time.





Thanks

Daniel

[348jeff]

A good starting point maybe to have a look here....

https://www.championautoparts.com/Parts-Matter/aut...

Which would you say most closely resembles yours and does it fit any other symptoms you may of had?

[A1VDY]

That's a good sign of the engine running very lean.
Have a gas test done to see where the co level is. It could well point to an injection/lambda problem..

[dhutch]

Hi, none of the photos I would say match what I see? I've had a look at a few guides and they suggestion was it's ash deposits due to worn valve guides or a lot of idling.

There are not other symptoms, the engine and car run very well, always serviced, and used daily for the last four years.

No lights on the dash, and recently passed it's mot. It did original fail on lambda but this was a hole in the backbox and was cured with a new rear box.

Thanks

[Boosted LS1]

Could you wire brush the earth electrodes and post up a pic? What fuel are you using? Are you a long distance driver sitting in cruise mode? If so the engine will run lean on purpose.

[dhutch]

If I fish then out of the bin!

I do use cruise control but not a huge amount.

Fuel is just normal pump petrol. Often shell as its local, but any other depending where I am when th light comes on!


Daniel

[DeadCatWalking]

A1VDY said:

That's a good sign of the engine running very lean.

No it absolutely isn't. It's a good sign of oil being burned.

[E-bmw]

^^^^ Correct, classic case of burnt oil deposits.

[A1VDY]

^^^
Disagree. The plugs getting too hot through a weak mixture will cause the white deposits.
If it's oil being burnt the plugs will just be oily..

[paintman]

Try these pics.
https://ngksparkplugs.com/en/resources/read-spark-...

[dhutch]

paintman said:

Try these pics.
https://ngksparkplugs.com/en/resources/read-spark-...

Oh I mean, it looks like the deposits pic on all of these guides.

https://www.wcpmx.com/How-to-read-a-spark-plug-s/7...

Obviously fuel wise, I'm using fresh brand name forecourt fuel in a week developed nation, so that shouldn't be an issue, certainly not beyond what is normal in the UK.

The car isn't left idling, and while obviously spends almost of it's time obeying the speed limit and time in traffic, also gets a good right foot a fair bit too like it should.

It's done 167k and these cars always use some oil, if in this case I think less than most of its age and milage, quite less than half a litre every 1000miles now if fixed the small weep on the oil filter housing.

Electronic fly by wire engine, lambda sensors etc, never had issues at MOT for emissions so presumably running as it should there.

Hence I'm wondering if it's just actually normal and part of expected build up. And or if there is anything to be learned from it.

[paintman]

With that mileage I wouldn't worry about it - although you might want to clean the plugs from time to time as a whisker of fouling from the centre electrode to a post will cause a misfire.

Edited by paintman on Wednesday 11th December 22:17

[Auntieroll]

A1VDY said:

^^^
Disagree. The plugs getting too hot through a weak mixture will cause the white deposits.
If it's oil being burnt the plugs will just be oily..

Wrong, if over lean the insulator will have a smooth ,white ,very light deposit or in extreme cases blistering which is obviously not the case in this instance.
The pale grey ash deposits seen here are generally a sign of oil being burnt by plugs having the correct heat range.
Black oily deposits mean that either the plugs heat range is wrong or the engine is in dire straits , again not in this instance.

[E-bmw]

Based on the fact that it is an M54 engine & burning oil as lots of them do, just keep on top of keeping the plugs clean and if anything increase the frequency of doing this & it should be fine.

I have had 2 of these engines, one did, one didn't. On the one that did burn oil I just used to have them out & clean them every 6 months & replace them every year.

[dhutch]

E-bmw said:

Based on the fact that it is an M54 engine & burning oil as lots of them do, just keep on top of keeping the plugs clean and if anything increase the frequency of doing this & it should be fine.

I have had 2 of these engines, one did, one didn't. On the one that did burn oil I just used to have them out & clean them every 6 months & replace them every year.

I mean that sounds like reasonable, practical, engine specific, knowledge.

Not sure how long the plugs have been in, there was a point about 2.5years ago when there was a reason to change them, and I had to make a call one way or the other, based on the fact that they were as far I knew last changed 2 years earlier shortly before I acquired the car, during its last 'Inspection II' service. However I cant recall which why i went or find the paperwork for that one way or the other.

So these plugs have been in for 2.5 or 4.5 years. at about 10k pa.

Sounds like the best thing to do is not worry, but keep a bit of an eye on it. I will try and get around to pulling a few plugs in 6-8months time and have a look at them, cleaning or replacing as appears sensible. I got charged a small fortune for the job this time, but it appears you can get a set of the right plugs NGK BKR6EQUP for about £35 off ebay.

I have recovered a handful of the old plugs from the bin, and while see what they look like after a light wire brushing tonight or over the weekend.

Daniel

[DeadCatWalking]

A1VDY said:

^^^
Disagree. The plugs getting too hot through a weak mixture will cause the white deposits.
If it's oil being burnt the plugs will just be oily..

When the amount of oil being burned is not excessive and the ignition system is working well then deposits like this are created. If the chambers are flooded with oil and/or the plugs aren't even firing anymore then they get oily. Weak mixtures produce very little in the way of deposits, usually a very white insulator and in extreme cases melted or rounded electrodes. These are classic deposits for plugs which haven't been changed in ages with above average but not excessive oil consumption.

Solution is simples. Clean/change the plugs more often. Pulling the engine apart and doing valve guides, stem seals , piston rings is an expensive option compared to adding a bit of oil every now and then. It'll soldier on for ages.

I once had a nacked 1275 A series Marina that used a gallon of oil in 100 miles. Now that's proper oil consumption. When you can't see the traffic behind you for oil smoke you get oily plugs.

[Higgs boson]

DeadCatWalking said:

I once had a knackered 1275 A series Marina that used a gallon of oil in 100 miles.

Now that's impressive!
I had a mate whose (A series) engine would do similar - but likely not just quite so bad .
We had a mutual friend who serviced motorcycles. He would provide the used oil from the bikes to permit daily topping up.

[dhutch]

DeadCatWalking said:

Solution is simples. Clean/change the plugs more often.

Sounds good.

Nothing mentioned about low quality oils, or anything else else which can practically be done.

The rate of oil loss is very mangable, on a par with the audi diesels from new, certainly no plans for a top end rebuild yet.


Daniel

[DeadCatWalking]

Higgs boson said:

DeadCatWalking said:

I once had a knackered 1275 A series Marina that used a gallon of oil in 100 miles.

Now that's impressive!
I had a mate whose (A series) engine would do similar - but likely not just quite so bad .
We had a mutual friend who serviced motorcycles. He would provide the used oil from the bikes to permit daily topping up.

Thinking back it was probably even higher oil consumption than that. I set off from Chorleywood to go to Taddington, Derbyshire (155 miles) to my uncle who was going to help me rebuild the engine. I had a full sump and a gallon can in the boot. 50 miles later up the M1 the oil light was on so pull over and put half the gallon can in. 50 more miles and pour in the rest. 10 miles outside Taddington on the A515 trying to negotiate the peak district hills it slowed and slowed until I could only use 1st and 2nd. It was seizing from lack of oil and overheating but I struggled on very slowly. I nursed it the last 10 miles and it finally seized half way up my uncle's driveway. I had to walk the rest of the way. Perfect timing really.

[Higgs boson]

DeadCatWalking said:

Higgs boson said:

DeadCatWalking said:

I once had a knackered 1275 A series Marina that used a gallon of oil in 100 miles.

Now that's impressive!
I had a mate whose (A series) engine would do similar - but likely not just quite so bad .
We had a mutual friend who serviced motorcycles. He would provide the used oil from the bikes to permit daily topping up.

Thinking back it was probably even higher oil consumption than that. I set off from Chorleywood to go to Taddington, Derbyshire (155 miles) to my uncle who was going to help me rebuild the engine. I had a full sump and a gallon can in the boot. 50 miles later up the M1 the oil light was on so pull over and put half the gallon can in. 50 more miles and pour in the rest. 10 miles outside Taddington on the A515 trying to negotiate the peak district hills it slowed and slowed until I could only use 1st and 2nd. It was seizing from lack of oil and overheating but I struggled on very slowly. I nursed it the last 10 miles and it finally seized half way up my uncle's driveway. I had to walk the rest of the way. Perfect timing really.