Running a 160 in place of a 180 will not keep any car from over-heating. When the engine is producing heat faster than it is being taken away you overheat. This can be caused by too small a radiator, fans not running correctly, bad thermostats or in your case no (or low) coolant flow. The thermostat just regulates the temperature of the coolant in the water jacket. Your
oil would prefer the 180.
Just my $0.02
Bob