Lugging and driving too fast have been the most frequent causes of overheating in the 4-cylinder engines. It's a good thing the thermostat has a built in leak because the stock radiator is big for the engine. Without that leak I'd be worried about shocking the engine when the thermostat does open. But, seeing that you live where it gets hot, you might benefit from a larger radiator.

__________________
daBenz - 1970 220D