but I think you are incorrect about 'voltage'.

If the fan is turned on by switching "ground", battery voltage will always be present at the fan terminals. So measuring voltage gets you nowhere. If it's always there, you learn nothing.

The killer here is that even if the fans NEVER come on, you will probably NEVER burn up the engine. There's many MBs whose fans are not working and they survive quite nicely.

But forget about fans per se; your last idea is still probably the best. We are REALLY interested if the car's engine temp gets to dangerous point. A ckt could be implemented relatively easily.

By setting a trip point for, say 110C, assuming that's a 'good' point, it could be implemented by an opamp with a "fixed" bias point. That, in turn, would trigger an alarm device; could even be a BRIGHT FLASHING LED. Just something to alert the driver to stop the car.

Now one steps back and asks . . how many times is this needed? I think the answer is not very often. At my tech's shop, I've only seen one car in 8+ years where the engine burned up. And even it was because the driver, a young teenager who had never driven an MB, didn't watch or even look at the gauges of his aunt's car. He had the radio on full blast!

I suppose this device we are talking about MIGHT have alerted him but not sure he would have paid attention even if he saw it! He certainly couldn't have "heard" it if it was audible.

Good idea but probably not very saleable. Nor useful.

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Regards . . . . JimF
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'94 S500 Cpe

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