It’s above 90°F the A/C is on, temp gauge has moved from normal to almost too hot what can be done? Most cooling systems today have a heater core built in for defrosting the windshield, cold weather heat or defogging in rainy weather.
Most people do not know that the heater circuit is on all the time in most applications. Hot coolant is circulating through the heater core under the dash, this coolant does not go through the radiator to dissipate heat and help cool the engine.
The heater circuit is a radiator bypass loop, some system have a control valve that shuts off the coolant flow when heat is not condition to help lower the temperature why not be more comfortable and let the radiator do it’s job.
To remedy this problem a simple manual valve can be installed in the heater feed line or a 1/4″ restriction can be fabricated and put in the hose. Before doing this make sure the hose you select only feeds the heater core.
By shutting off or restricting this circuit it redirects the coolant flow to the radiator where the operating temperature can be decreased by 10 to 20 degrees.