Vehicles used at high performance levels like frequent HPDE participation should have their plugs changed at frequent intervals, nothing wasteful about that; normal street mileage intervals do not apply.
Light tan is an indicator of correct fuel mixture. These plugs are a tad too cold.
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Ok here is the pic of the topside of the plugs and again the order is 1-2-3-4:
Note the black carbon deposits above the plug seating surface on plugs 2-4. It is limited by the boot fitting snugly around the insulator about halfway up. Look at plug #1 above the gasket, they should all look like that, perfectly clean.
Carbon deposits above the seating surface means that the plug was not tight enough and combustion gasses were blowing-by the gasket/seat. This is...... uh...... bad. The terminal nuts were also loose on those plugs and they did not require a ratchet wrench to remove, they were essentially loose. The terminal nuts were likewise loose on those 3 plugs.
Today the problem is minor, maybe a little performance/ efficiency loss. Left alone the plug would have just kept getting more loose until it starts throwing codes and/or one of them gets blown out of the head.
The warning is to check those spark plugs. When installed these were torqued to 20ft-lbs as per spec, somehow that was not sufficient to keep them seated properly. Checking them is not really hard and something I should have done more often.
With a crush gasket style of plug, the plug manufacturer will typically indicate an installation torque or tightness of 1/2 to 2/3 of an additional turn after the gasket touches the seating surface on the head. Using a torque wrench you will hit 20lbs before you get to a half turn. So this time I made sure to use a little anti-seize lube and went with the half turn tightness which would be closer to ~25 or maybe even ~30ft-lbs. Still, I think I will check them after they go through a few heat cycles.
Crisis Averted! :^)-
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