When a car is warmed up and at normal operating temperature. One turns on the heater for heat.
Does the having the heater on reduce the heat of an engine by letting the hot air escape?
If a car is on the verge of overheating...would turning on the heater lower the engine temperature a little?
Does the having the heater on reduce the heat of an engine
yes
by letting the hot air escape
heat from the engine is picked up by the coolant. The coolant is pumped to the heater core, carrying the heat with it. Air from the blower motor picks up the heat from the core, and blows it out your vents.
If a car is on the verge of overheating...would turning on the heater lower the engine temperature a little?
Yes, but the pump and engine must be running. It can help to a point, but if the overheating is serious enough (temp is running away) then it's better to shut it off.
Unless you have an air-cooled engine, hot air "escaping" from the engine has absolutely nothing to do with the heater in the car.
If a car is overheating running the heater may help as long as overheating is not caused by loss of coolant.
When you open the heater, coolant flows thru the heater core, essentially a second radiator. As soon as the engine reached operating temperature and the thermostat opens, the engine will get back to near normal temperature. If you see the car overheating, turning on the heat will temporarily cool it down so hopefully, you can get home and not blow a head gasket or a radiator. A good radiator cap will help a little by dumping over pressurized coolant into the reservoir.
Great. Thanks.