Troubleshooting car problems of temperature gauge that reads hot
Temperature gauge that read hot after starting is an indication of three possible reasons, lack of coolant, damage radiator hoses, or a bad water pump or thermostat.
First thing to do is to check the car if there is sufficient amount of coolant in the radiator, look into the radiator fill hole (do this only after the engine cools down) and check if the coolant level covers the metal fins inside the radiator. If the coolant level did not covers the radiator metal fin then the radiator lacks coolant which is why this kind of problem occurs.
However, If the amount of coolant is sufficient enough then the next thing to do is to look at is the radiator hose. In doing this you must start the engine first and observed the radiator hose, look for the collapsing hose. If the radiator hose collapse this prevents the flow of coolant from the radiator into the engine in this case the coolant heats up shortly after starting the engine causing the temperature gauge to indicate hot temperature.
Now, if radiator hose is in good condition then this is the case of either bad water pump or thermostat. The purpose of water pump is to circulates coolant from the engine into the radiator and back to the engine. If the water pump is defective there will be no circulation of coolant and the coolant will become too hot. This will make the temperature gauge reads hot. Likewise if the thermostat is bad this can cause the problem, because thermostat is the one that keeps the coolant to reach the radiator when the engine is cold. When the engine warms up the thermostat will open then it allows the coolant from the engine to reach the radiator. Possible
Cause of Temperature Gauges that Reads High
Insufficient amount of coolant, collapse radiator hose, or a bad water pump or thermostat
How to Fix Temperature Gauge that Reads Hot
For the insufficient amount of coolant just ad the necessary amount of coolant, a 50/50 mix of water and anti-freeze will do, however you must also take into consideration why the radiator lacks coolant? There might be a leak somewhere in the system. It might also possible that there is an internal leak usually causes by a blown head gasket you can easily determine if this is the cause when there is a white smoke that comes out the exhaust while your driving, have your car check by a mechanic to make sure. As for the collapsing radiator hose, no other option but to replace the affected parts.
As for the bad water pump or thermostat, bring your car to a reputable auto repair shop and ask the mechanic to inspect the water pump and the thermostat to determine which of the two is the cause and replace if necessary to avoid temperature gauge that reads hot after starting the engine.