Just changed the plugs on my van, and wanted to see if they could tell me anything about how the engine is doing. NGK's spark plug reading tips are here: http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp The plugs that came out of the Domingo had a rounded center electrode and a pretty big gap, so they were definitely due for a change. However, they don't tell me much about what's going on in the engine. The plugs have: a white colored side electrode, all the way until it meets the ring (so engine too lean or spark plug type "too hot"?) black soot around the ring (so running 'too rich'?) two-tone center electrode (seems OK.) As far as I can tell, looks good. Peering into the cylinder, the piston head was mostly covered in black grime on it. Normal for a 60,000km engine? Now the spark plug location in the Domingo, that's another story.