I have a wierd cooling issue on a 2000 mustang get. When I go uphill (even slightly), the coolant temp immediately rises to 200 degrees. When I go downhill (even slightly), coolant immediately goes down to 180 degrees. When driving level, the temp stays at 180. The car has a new 2-core aluminum radiator, new Edelbrock high flow water pump, new 180 thermostat and new ect sensor. I am using an Aeroforce obd gauge to monitor the coolant temps. No bubbles in radiator, no oil in coolant and engine oil is not milky. I also did a combustion leak test to check for a blown head gasket and the test was negative. I did a pressure test of the cooling system, and no leaks were found.
Any other things to check?
Any other things to check?