Hello!

I was talking to a friend of mine who also has a 123, who had paid a visit to an old mechanic who had supposedly been trained at Stuttgart. The mechaic told my friend something that really surprised me.

The mechanic was advising that my friend make some sort of modification to the thermostat to make the car run cooler, and that doing this would make the car run more efficiently, have more power, and get better fuel mileage.

Now, I've been under the impression that diesels prefer to run hotter, and are actually at their most efficient at a temperature right below the point where the metal can't tolerate the heat anymore. Obviously, we don't want to run the engines at this high of a temperature (whatever it may be) because the engine won't last as long, BUT, we don't want the engine to run too cool either. This is why thermostats are installed instead of leaving the space open for the coolant to flow freely.

Do I have this wrong, or does the mechanic not know what he's talking about (or is going off an old wives' tale)?

Thanks!