I doubt that a glow plug would heat up the air enough to help. You would need something similar to an electric strip heater that is used in electric furnaces. The glow plug works inside the engine, because the space is so small and you are looking for a high temperature device to start the combustion process only, not transfer heat.

Why not look into a block heater...this is a guaranteed fix for your problem? If you don't have one, I have heard that the ones that attach to the oil pan do a pretty fair job, as well.

Good luck!

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold