Premium Vs Regular gas in Mercedes

Hello, Quick question about the "unleaded premium fuel" notice on the gauge of most every sedan I have driven...
I wondered since I was driving used cars, if ever
the previous owners ran regular vs premium gas and if so what damage could or have they done?
What happens to the engine if a tank of regular is put in by mistake or by an owner who didn't want to pay Premium price at the pump.
Just curious, figured you guys/gals here would know.
Bill :)
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Well, seeing how mostly modern cars are the ones asking for premium fuel, I'm going to assume we are talking about modern cars here. Running low octane causes the engine to knock. Modern cars have pretty decent knock sensors where they retard timing when the octane is too low. This degrades performance and smoothness of the ride, but it shouldn't do any damage. I suppose if you did it for like 10 years it might, but not over a short period of time. Richard

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I forgot to mention, if it's got a turbo or supercharger, then it would be very very bad to run low octane. Richard

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Preignition of poor fuel causes excessive heat and also hammers the valve train.

It's probably not a big deal, but if it was chronic and in a hot climate it could definitely contribute to an early demise. Especially if the car was driven very hard...
Marty
PS my 1986 190e likes the premium but does ok on the mid grade as well...
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