About 4 years ago, my thermostat failed and the temp guage went to max plus the coolant was boiling out of the expansion tank before I could get pulled over. I ended up replacing the thermostat where I stopped the car and it has run fine for about 60K miles since then. So if the engine can take that much stress, you should have no problem...
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96 850T, Bilstein HD, IPD swaybars-HD endlinks

thanks guys! and thank goodness for that dummy light. if it hadn't blinked, i would have ignored it, thinking it was the service light...

paul
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1982 240 DL (265K) , 1996 850 GLT (125K)

I thought I saw where the gauge isn't updated constantly, and may not respond immediately to an actual change.

That being said, I don't see any way that your problem caused any damage to your engine. I remember when my resevoir tank cap was bad, it leaked very slowly until the light would come on. I'd top things off, and over months the same thing would happen again. A half gallon isn't enough to stop circulation, that is for sure. That particular idiot light gives you fair warning.