I pulled them today to check and regap them. They don't look quite right - the ceramic is totaly white, there is carbon soot between the ceramic and thread (which falls out when you tap them). The ground and center electrode have light grey deposits and they were around 1.1mm gap after 4k miles. They are the stock NGKBCPR7ES. Directing a small flashlight into the plug holes I could see a few flakey black carbon deposits on the piston tops. My economy is good and I'm not burning oil and recently I've been driving quite conservativley. One thing that does slightly concern me is that the rad fan seems to be very active - has been since I had it. This would also indicate the engine is running hot although the needle never goes over 1/2 and I'm not loosing coolant.