Recognition feature |
Reason/Features |
| A. The apex of the thermal cone of the insulator is light gray to gray. | Spark plugs are installed with the specified heat rating. Engine management (fuel mixture preparation, ignition system) operates according to the specifications, mechanical wear is within the permissible values. |
|
B. The top of the thermal cone of the insulator is whitish in color. |
The insulator is overheated. Bad (faulty) fuel. Leaky valves. Valve clearance too small. Exhaust gas measurement should be performed. Check engine management, possibly lean fuel mixture. If in doubt, you risk major engine damage (piston scuffing, piston burnout, exhaust valve burnout). |
| IN. The appearance of the screw-in part of the spark plug is dark, the insulator is black. | Spark plugs are installed with a high heat rating. Spark plugs are worn. High proportion of short-distance driving. Air filter is closed. Engine management should be adjusted. Lambda sensor is not working correctly. Exhaust gases are black. |
| G. The appearance of the screw-in part of the spark plug is black, the insulator is oily. | See B. High-voltage ignition cable, spark plug plug defective. Piston oil scraper ring torn. Piston scoring. Valve stem gasket worn. High oil consumption. Blue-black exhaust gas. |
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