greiswig wrote:
Glow plugs provide a point of temperature within the combustion chamber that is way beyond the flash point of the fuel, so that no matter what the temperature of the air in the cylinder is, or what the temp of the combustion chamber is, a flame front can start. In this sense they are analogous to a spark plug, which does not electrify or heat the entire air/fuel charge. They don't heat the air or the chamber in toto, nor do they affect the viscosity of the fuel in any way.
Many diesel engines (my Unimog for example) have no glow plugs, and they usually start just fine. But it's a more reliable start with them, especially at very low temperatures.
I think that the biggest drawback to ignoring the glow plugs or to not having them is that unignited fuel washes the cylinder walls and gets down into the oil, eventually reducing its effectiveness. It also reduces your battery life, since it takes more cranking than if the glow plugs were working properly.
That and the fact the engine does not fire till after the GP's lite up says it all, you are worrying about nothng.
Our VW's didn't have the instant on GP's and the delay circuit to prevent starting w/o GP's and I would sometime switch between the gasser car and the diesel and forget to allow the GP's to warm up and would have a hard crank. I did it once at -2F and the car started and run on about the 3rd compression stroke, I was impressed with the TDI but realized it was as much the high quality 50 cetane fuel I was using at the time.