How long can a glow plug stay on before there are issues?
The glow plugs on every vehicle that I have ever worked on that come on when the key is turned on will have a timer unit. This timer unit limits how long the glow plugs will stay on each time the key is turned on. You can damage the glow plugs if you continue to cycle the key several times.
The glow plugs can get a carbon build up on them from the normal engine combustion process and when you go to use them they will not heat up enough to help start the engine when it is really cold out. The carbon can be cleaned off of them and reinstalled if the glow plug tests good.
If you run into any issues, consider having your glow plugs and timer serviced at your home or office by a mobile technician from YourMechanic.
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