Yesterday I changed my spark plugs after old ones had been driving about 5000 miles. I've heard that the condition of spark plugs can say a lot about the engine, so it would be nice if somebody could give me some idea, what's wrong with mine (B230F, LH-Jet 2.4).

All the previous times (I change plugs every 5000-10000 miles) electrodes came ususally covered by gas, slightly gone black. But this time the electrodes have sand-yellow / orange / bright-rust color, are completely dry and look "corroded". Unfortunately no digicam to post the photos. BTW, plugs are NGK V-Line BPR-6-E(S)

In addition I can say, that temp gauge pointed normally at 8 o'clock in the days of "oily" plugs and now is pointing usually at 9 o'clock (engine runs hotter).

I've checked also the O2 sensor (Lambda Sond) voltage: 0V from sensor side, 25 mV average from ECU side (why?), ground OK, heating OK. Because of financial reasons I can not get a new one now, but generally I'm satisified with fuel consuption even without that sensor. Please don't take the catalytic converter damage and emissions into matter.

Thanks in advance.