I have a 92 300D. As of late, I have been noticing the following: a few moments after the engine starts, the glow plug light will come on, stay on for about 30 seconds, then go out. But just in the past few days, it has not been coming on when I turn the key, but then does come on for about 30 seconds while driving.

Any thoughts as to what's going on?

Also, above what ambient temperature is the glow plug system unnecessary? As I live in Texas, I'm hoping I won't have to fix whatever's wrong until it gets cooler.

Thanks.

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 163k miles
06 E320 CDI "Rutherford", Black on Tan, 182k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 147k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 82k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife