At any speed your car temperature gauge reads hot when the weather is hot, even when driving at fast the air that hits the radiator is not sufficient to cool the coolant.
Car Problem Diagnosis
Open your car hood and remove the radiator cap, (caution: Do not remove the radiator cap while the engine is hot), check the coolant level by looking down the radiator fill hole, coolant level is sufficient if it covers the little metal fins inside your car radiator. If the coolant level is sufficient then the problem is clogged radiator.
Possible Cause of Temperature Gauge That Reads Hot on Hot Weather
Lack of engine coolant or clogged radiator.
Ho to Fix With High Temperature Reading on Hot Weather
First thing to do is to clean any debris or bugs of the face of your car radiator. You can do this using a hot water and a soft brush.
Second, have your car entire cooling system back flushed. back flushed is done by running water inside your cooling system opposite the direction of the normal flow of coolant through your car entire cooling system. This is done to remove rust and other particles that building up inside your car cooling system and restore the efficiency of your radiator and other cooling system parts. You may do the back flush yourself since you can buy a back flush kit in any auto shop and it’s easy to use.