DualCamCoupe
08-30-2003, 09:21 PM
I found this useful so I thought I'd pass it along.
http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp?nav=31200&country=US
Q: How do I "read" a spark plug?
A: Being able to "read" a spark plug can be a valuable tuning aid. By examining the insulator firing nose color, an experienced engine tuner can determine a great deal about the engine's overall operating condition.
In general, a light tan/gray color tells you that the spark plug is operating at optimum temperature and that the engine is in good condition. Dark coloring, such as heavy black wet or dry deposits can indicate an overly-rich condition, too cold a heat range spark plug, a possible vacuum leak, low compression, overly retarded timing or too large a plug gap.
If the deposits are wet, it can be an indication of a breached head gasket, poor oil control from ring or valvetrain problems or an extremely rich condition - depending on the nature of the liquid present at the firing tip.
Signs of fouling or excessive heat must be traced quickly to prevent further deterioration of performance and possible engine damage.
Normal Condition
An engine's condition can be judged by the appearance of the spark plug's firing end. If the firing end of a spark plug is brown or light gray, the condition can be judged to be good and the spark plug is functioning optimally.
http://www.ngksparkplugs.com/images/readnormal.jpg
Dry and Wet Fouling
Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon.
http://www.ngksparkplugs.com/images/readdryandwet.jpg
Overheating
When a spark plug overheats, deposits that have accumulated on the insulator tip melt and give the insulator tip a glazed or glossy appearance.
http://www.ngksparkplugs.com/images/readoverheating.jpg
Deposits
The accumulation of deposits on the firing end is influenced by oil leakage, fuel quality and the engine's operating duration.
http://www.ngksparkplugs.com/images/readdeposits.jpg
Lead Fouling
Lead fouling usually appears as yellowish brown deposits on the insulator nose. This can not be detected by a resitsance tester at room temperature. Lead compounds combine at different temperatures. Those formed at 370-470°C (700-790°F) having the greatest influence on lead resistance.
http://www.ngksparkplugs.com/images/readlead.jpg
http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp?nav=31200&country=US
Q: How do I "read" a spark plug?
A: Being able to "read" a spark plug can be a valuable tuning aid. By examining the insulator firing nose color, an experienced engine tuner can determine a great deal about the engine's overall operating condition.
In general, a light tan/gray color tells you that the spark plug is operating at optimum temperature and that the engine is in good condition. Dark coloring, such as heavy black wet or dry deposits can indicate an overly-rich condition, too cold a heat range spark plug, a possible vacuum leak, low compression, overly retarded timing or too large a plug gap.
If the deposits are wet, it can be an indication of a breached head gasket, poor oil control from ring or valvetrain problems or an extremely rich condition - depending on the nature of the liquid present at the firing tip.
Signs of fouling or excessive heat must be traced quickly to prevent further deterioration of performance and possible engine damage.
Normal Condition
An engine's condition can be judged by the appearance of the spark plug's firing end. If the firing end of a spark plug is brown or light gray, the condition can be judged to be good and the spark plug is functioning optimally.
http://www.ngksparkplugs.com/images/readnormal.jpg
Dry and Wet Fouling
Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon.
http://www.ngksparkplugs.com/images/readdryandwet.jpg
Overheating
When a spark plug overheats, deposits that have accumulated on the insulator tip melt and give the insulator tip a glazed or glossy appearance.
http://www.ngksparkplugs.com/images/readoverheating.jpg
Deposits
The accumulation of deposits on the firing end is influenced by oil leakage, fuel quality and the engine's operating duration.
http://www.ngksparkplugs.com/images/readdeposits.jpg
Lead Fouling
Lead fouling usually appears as yellowish brown deposits on the insulator nose. This can not be detected by a resitsance tester at room temperature. Lead compounds combine at different temperatures. Those formed at 370-470°C (700-790°F) having the greatest influence on lead resistance.
http://www.ngksparkplugs.com/images/readlead.jpg