Why Is My Car Overheating But It Has Coolant In It

You probably ask yourself ”why is my car overheating but it has coolant in it?” A lot of people think that engines overheat only when the cooling system has low levels of coolant. But, that is not always the case. Your car could be good on coolant and the engine can still overheat. Here is why:

Why is my car overheating but it has coolant in itOpens in a new tab.


Why Is My Car Overheating But It Has Coolant In It

Why Is My Car Overheating But It Has Coolant In It

Your car can have sufficient levels of coolant and your engine can still overheat due to other reasons. For the engine to keep a steady operating temperature and not overheat, the coolant has to circulate around the engine and remove the excess heat. If for some reason the coolant is not circulating, the engine will overheat. Here are the most common reasons why your carOpens in a new tab.

1. Failed Water Pump

Why Is My Car Overheating But It Has Coolant In It

A failed water pump can cause your car to overheat even if it has enough coolant in the radiator. The water pump has a job to keep the coolant in the engine circulating and therefore preventing your engine from overheating. If the coolant doesn’t circulate, then it’s going to boil next to the hottest parts of the engine and elsewhere it’ll be cold.

The water pump has a pulley and can be driven by a belt from the crankshaft, by the timing belt, or directly off the camshaft or crankshaft. That means that when the engine is running then the water pump is also running.

When your engine is cold, the thermostat is in a closed position. When in the closed position, it isn’t allowing any coolant to pass through the radiator. But, we still need to circulate that coolant within the engines that there’s even heating going on inside. That means that the water pump is always pumping.

Almost all car engines operate at a temperature of 200 degrees Fahrenheit or 90 degrees Celsius. That temperature allows for a nice flow of oil and steady combustion in the cylinders. It is also not hot enough to damage any components of the engine.

The engine parts which are close to the combustion process need to be cooled down. That’s why we need the coolant system. Coolant, which is a mix of water and ethylene glycol, is used to carry the heat away from the hottest parts of the engine and out to the radiator where it’s cooled down.

Now, when the engine is at operating temperature, a cold coolant is pulled out of the bottom of the radiator by the water pumpOpens in a new tab.

2. Clogged Radiator

Clogged Radiator

A clogged radiator can cause your engine to overheat even if you have enough coolant in the system because the coolant won’t be able to circulate properly through the clogged radiator and cool down.

The car radiator is a pretty simple part of the cooling system. As the coolant circulates around the engine it gets hot by removing the heat from the engine components. Once the coolant gets hot, it has to pass through the radiator. There it will cool down thanks to the atmosphere airflow.

A car radiator can get clogged and the coolant circulation will be restricted. The cooling system is a closed pressurized system. But, the cooling system can get clogged by dirt and debris. This will compromise the cooling effectiveness of the cooling system. If the radiator input where the hot coolant comes in is clogged, the coolant won’t be able to enter the radiator and to get cooled down. This will disrupt the steady and continuous circulation of the coolant and your engine will overheat.Opens in a new tab.

3. Thermostat stuck in closed position

Thermostat stuck in closed position

Your car can overheat even with enough coolant in the system if the thermostat is stuck in a closed position and not allowing the coolant to circulate and cool down the engine components.

When the engine is cold, we want it to get it up to temperature as fast as possible. So, the thermostat is closed and the coolant stays inside the engine system until it’s warmed up. Once that coolant is up to temperature, we want to start cooling it down. So, the thermostatOpens in a new tab.

If the thermostat gets stuck in a closed position, the engine temperature will rise and rise until the engine overheats. Because the thermostat is closed, the coolant won’t be able to travel around the engine and cool it down.

Igor Iwanowski

I am a certified Automotive Service Excellence (ASE) mechanic since 2018. I specialize in Brake systems, dashboard warning lights, EGRs, general engine problems, EVAP and Emissions issues.

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