Temperature Gauge Read Hot After the Engine Start

The temperature gauge reads hot after the engine is started. Several reasons are causing this such as the radiator lacks coolant, the hose of the radiator is collapsed, the water pump is faulty, or there is a problem with the thermostat.

Possible cause of temperature gauge that reads hot after starting

1) The radiator lacks coolant
2) The radiator hose is collapsed
3) The water pump is faulty
4) The thermostat is faulty

The listed reasons above the first two is the easiest to check. Now the first thing to do is to check the radiator if there is enough coolant on the system. Open the hood and locate the radiator, remove the radiator cap. Make sure that the engine is cold before removing the radiator cap otherwise you may burn yourself. Using a flashlight look down at the radiator fill hole to check the coolant level, the coolant level is said to be enough when the coolant covers the fins inside the radiator. If the coolant did not cover the radiator fins then the coolant inside the radiator is not enough and this causes the temperature gauge to reads hot. To work efficiently the engine cooling system must have enough coolant if the coolant is not enough the engine will heats up too quickly and the temperature gauge will register hot.

If there is enough coolant on the radiator, the next thing to check is the radiator hose. While the hood is opened locate the radiator hose. Refer to manual if you are having difficulties in finding the radiator hose. Ask a friend to start the engine while you observed the radiator hose, watch the hose until the engine gets hot. Look closely if the hose is collapsing, usually an old hose or a defective hose behave like there is pinching the hose.

If the radiator hose is collapsing then this causes the temperature gauge to read hot. When the hose is collapsing the coolant will be prevented from flowing in the radiator into the engine. This will cause the coolant to heat up quickly.

If the hose is not collapsing then the possible cause of the problem is a faulty water pump or a faulty thermostat. The water pump is the one that pump the coolant out of the radiator going inside the engine and back to the radiator. If the water pump is faulty the coolant will not be circulated through the radiator and will get hot and the temperature gauge will reads hot.
Water Pump image credit

Now for thermostat, the purpose is opposite that of the water pump this is because the thermostat is what keeping the coolant from getting into the radiator when the cold engine is started. Initially the thermostat is in closed position. After the engine warms up the thermostat will open to allow the coolant from the engine to reach the radiator. If the thermostat is faulty such as when the thermostat is stuck on the closed position the coolant that surrounds the engine will get hot and the temperature gauge will read hot.

freecardiagnostic.com image
Thermostat image credit

How to fix the temperature gauge that reads hot after the engine start

Radiator Lacks Coolant

Make a 50/50 mix of anti-freeze and water in an empty container, you can buy anti-freeze fluid at any parts store. During morning when the engine is cold, remove the radiator cap and pour enough amount of coolant to the radiator, the coolant must cover the fins inside the radiator. Now the problem is why the radiator lacks amount of coolant, there might be leak somewhere on the system. Have the cooling system check to make sure there is no leak on the system.

Collapsed Radiator Hose

Just replace the radiator hose with new one.

Faulty Water Pump or Faulty Thermostat

Bring the car to a car shop then have a mechanic to check the water pump or thermostat to determine which of the two causes the problem. Replace the faulty parts to fix the problem.

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