What Can I learn From My Spark Plugs?

[darchard]

Greetings all,
I bought my second 2003 Z4 3.0 recently and am thinking about changing the spark plugs as I don't know how old they are and whether they are in good condition or not. So I had a quick look at them today and they are all Bosch R3 Platinum (is that good?)
I took some photos and wondered if anyone can tell me anything about the state of the engine or anything else useful based on the images? To me they look a bit oily and corroded in a few places, so I guess they need replacing, or do they just need a bit of a clean up?
I'm also not sure what plugs to replace them with (assuming they do need replacing). Is it really worth spending more hard earned cash on expensive ones or are the cheaper ones just as good?
Thanks very much in advance guys for all your help,

 

[Chippie]

To me they look fine, I’d just give them a clean and put them back in.

 

[colb]

Tips look a good biscuit colour which indicates engine is running fine fuel mixture wise. Where is what looks like oil on the threads coming from?
May be look down the plug hole wells and see if oil is leaking into the bottom from a failed cam cover centre gasket that should be keeping oil out of the plug wells. If that's where the oil is seeping in then time to change the entire cam cover gasket. I always use an Elring brand gasket set that includes the cam cover 15 round rubber seals that go under the cover retaining bolts and Blue Hylomar gasket sealant only around the half moon shapes front and back of the cover and between the Vanos at the front. Sealant is required at these points where the gasket changes direction. The rest of the gasket mating surface is ribbed and provides the seal so no sealant required. The round rubber seals do go hard like the main gaskets from age and repeated heat cycles so wont compress when its put back together hence requirement to replace these as well as the gaskets.
All of these gaskets and seals are important for the car to run correctly, leaks not only let oil out but air in and this unmetered air that has not been measured by the Maf will be picked up by the exhaust sensors fooling the car into thinking its running lean which it then tries to correct by increasing fuel at the injectors to richen it up. It will keep doing this until it realises its not correcting and when its adding up to 20% more fuel it will give up and light the engine management light on the dash to draw attention to the fault.
Gasket example here, but do check against your cars details, example is for 3.0i E85

https://www.autodoc.co.uk/elring/7625587

 

[Rockhopper]

I don't think its considered good practice to clean plugs these days, especially if they have an iridium coating as you'll just take it all off (its very fragile).
In all my years of tinkering with cars I've never seen any improvement made by changing plugs, they either work or they don't. If they don't, change them, if they do, leave them alone.
Yours look a bit more carbony than I'd have expected, maybe a symptom of repeated short journeys? It'd be easier to see with some photos taken a bit further away.

 

[darchard]

To me they look fine, I’d just give them a clean and put them back in.

Hi Chippie,
Thanks for the reassurance... I'd much prefer to clean them up rather than replace them.
To clean them I guess I would:-
1. Wipe it down with a rag to remove the grime
2. Spray the end with a bit of brake cleaner and let it dry for a few minutes
3. Use a wire brush to remove the carbon build-up from the bottom of the threads and the outside and sides of the side electrodes
4. Use emery paper to clean up the inside surfaces of the side electrodes

--> Is it ok to use a wire brush and emery paper on the center electrode or are they a bit delicate?
--> Should I try to check and adjust the gaps with a feeler gauge? I've done this with spark plugs with a single side electrode, but I've never tackled one with four side electrodes before. Is it the same process? Does anyone know the correct gap setting?

Sorry if this is all very basic stuff but I'd like to get it right first time!

 

[Chippie]

I’d just give the threads a wipe, I don’t think a bit of brake cleaner would hurt or a small wire brush, just avoid the tips, not sure how you would adjust the gap so best left as is.

 

[darchard]

So I gave the plugs a bit of a wipe and brush up and put them back in. That saved me a few quid so thanks for the advice!
I took a peek down the plug wells and they all look nice and clean and shiny so I guess my cam cover gasket is still fine. I did notice some sealant peeking from the join on one corner so I guess that was done at some time in the past.
I guess that still leaves the mystery of where the oil on the plug threads came from so I'll keep an eye on it and see how it goes.
Thanks again guys and happy driving!

 

[Chippie]

So I gave the plugs a bit of a wipe and brush up and put them back in. That saved me a few quid so thanks for the advice!
I took a peek down the plug wells and they all look nice and clean and shiny so I guess my cam cover gasket is still fine. I did notice some sealant peeking from the join on one corner so I guess that was done at some time in the past.
I guess that still leaves the mystery of where the oil on the plug threads came from so I'll keep an eye on it and see how it goes.
Thanks again guys and happy driving!

Glad everything looks ok, perhaps the gasket had been replaced previously and the oil on the plugs is just old residue from before.

 

[x-driver]

Spark plugs are supposed to be replaced every 50-60.000km. If you don't know how old are they, replace them and mind the mileage for the next time. Spark plugs can go bad internally and you won't always see it from outside.