For a diesel to start, you need good compression, and good cranking speed. If either doesn't exist you could have trouble starting the car even with properly-operating glow-plugs.

I'm going to have to assume that you know how to start the car properly, as you imply that you've had it for at least 7,000miles, however:

The glow plugs will stay on after the light turns off. In fact, the light timer sometimes goes bad and turns the light off early. Anyway, turn the key to glow, let it glow for 30seconds and see how it starts. You can tell when the glow-plugs turn off by the brightness of the dome light, the speed of the blower, or the click of the relay.

And yes, starting fluid is very bad for an engine, especially a glowplug engine.

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Gone to the dark side

- Jeff