Are Discolored Glow Plug Threads Normal?
I’m a newbie to RC and just purchased a nitro powered ready-to-run truck a couple of weeks ago. The glow plug that came with the engine failed, so I replaced it with a new one of the same specification. I always use after-run oil and I noticed that the threads on the glow plug are discolored, but the coil still looks good. Is the discoloration on the threads a problem?
The discoloration is most likely just the burned oil that is mixed in to every nitro fuel blend. The threads of the glow plug locate it in the head, but it is the copper washer that gets crushed and makes the air-tight seal. The combustion products can work their way into the thread teeth, but cannot get past the washer and this includes the burned oil. If the washer is damaged or the glow plug is not fully tightened into the motor, it will allow more burned oil to get to the threads than it normally would. New glow plugs come with a new copper washer and the old glow plug washer should not be reused on the new glow plug, which may cause a leaky seal. If the performance didn't change drastically after the glow plug change, it’s probably fine. Just make sure to get the glow plug tight between after-run oil applications, and to help your tuning, invest in a temperature gauge to keep track of head temperatures.