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[Ken T]

You know when you check your plugs, if they are white, then running too lean and if a light tan colour then OK. Well I changed mine today, and the old ones are both colours, one side is white, and the other is tan!. Thats on all four plugs. Does this mean the mixture's not mixing/burning properly. The gaps looked a bit wider than the repacements. Also the sealing ring round 3 of the plugs was rusty. What's going on !

[Kevin Wood]

Sounds normal to me. Modern fuel doesn't leave much colour on the plugs unlike the old leaded fuel. This often gives the appearance of running lean but IME it's OK. Engine management would complain if it was having trouble adjusting the mixture anyway due to feedback, or lack thereof, from the Lambda sensor.

Depends how the car was last driven too. If you got the plugs nice and hot they will look very clean. If you left it idling on the driveway for ages they'll be sooty.

The rust is probably a bit of condensation that's got into the plug wells at some point.

The gap on a plug will increase as it wears and new plugs are generally correctly gapped. Worth checking them before putting them in but electronic ignition systems will work over a wide range of gap sizes so it's not necessary to keep adjusting them. Probably best to fit and forget until the next change is due, unless you have reason to believe the plugs are misbehaving.

Kevin

[JamesV6CDX]

Mine were like that, I don't think it's any cause for concern.

[Marks DTM Calib]

Not that surprising, the correct colour tends to appear around the electrode (they are twin electrode) which is firing and hence the variation in colour

[Markjay]

Yep, mine were like that as well...