I had the Thermostat replaced a Nissan dealer and installed a new radiator cap. The coolant was replaced and it has a 60/40 mix of anti-freeze and water. Since the coolant was replaced the engine will not heat up enough to make the thermostat open. The temperature gauge does not show the engine temperature rising up to normal operating range. The engine never overheats and the heater produces decent heat at idle or at highway speed. The engine used to warm up to the proper operating temperature before changing the thermostat and coolant. The dealer installed a lower radiator hose engine block heater as I live Edmonton, Alberta Canada and the temperatures go really low. The car is well-maintained and the coolant has been changed per the owner's manual. I feel the upper radiator hose and it never gets hot. The engine is warm and all the bi-pass hoses are hot. The radiator is not very hot. After running on the highway for an hour the car may or may not be hot enough for the thermostat to open and the coolant will flow thru the radiator. Any ideas?