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Top 7 Reasons Car Overheats – Warning You

If your car overheats it can be costly. Here you can learn the common reasons why a car engine overheats and what to do. Number 7 is very costly so do these checks to avoid.

You can also learn what the different components are that make up an engine cooling system and understand their function to help you identify any immediate problems or likely future problems that could be costly.

Don’t Ignore the Warning Signs of an Overheating Engine

A car engine overheats when the coolant (water and alcohol) starts to boil but before it gets to that point there are warning signs that you need to pay attention to and act quickly.

Warning Signs Car Overheats

Temperature Gauge Rising

If your temperature gauge is showing the needle above its normal position or starts rising then you need to act quickly. Most modern vehicles will show the needle in the same position irrespective of the warmer months because they use electric fans that come on and off to control the engine temperature. So if you find the temperature gauge showing a different reading than normal you can safely assume something is wrong and you need to do some basic checks.

Also, depending on the amount of carbon build-up on the top of the pistons you may start to hear a pinging sound. This is the pre-ignition phase where the fuel is igniting too early in the engine cylinders.

Hissing, Whooshing Noise & Steam from Under the Hood

If you hear a splashing noise as the coolant hits the hot parts of the engine and gives off large white steam clouds that come out from under the hood you know you have a problem. The car is already overheating.

Engine Sounds Like Ball Bearings In a Can

This is severe and caused by extreme heat that has made the engine oil thin out and lose its lubricating properties. Damage is being done to the bearings and other surfaces in the engine.

Also, you will start to hear a detonation sound (engine knock) and this causes metal components in the engine, like pistons, piston rings to start cracking or melting.

Why Your Car Overheats?

  • Blockage – The cooling system can fill quickly with rust and corrosion. A build up of rust or scale can cause a blockage in the radiator cores or water jackets in the engine (mineral deposits prevent proper heat transfer).
  • Faulty Thermostat – Not opening and restricting coolant flow to radiator.
  • Loose Drive Belt – Drive belt slips preventing water pump to circulate coolant efficiently.
  • Faulty water pump – Leaking, bearing noise or broken pump shaft are all visible or audible. It’s also common for the impeller of the water pump to become corroded and lose its ability to pump the coolant efficiently through the cooling system causing the engine to overheat at higher speeds.
  • Missing fan shroud or ducting – Reducing airflow through radiator.
  • Engine fan problems – Fan clutch or electric fan problems prevent adequate air flow through the radiator.
  • Major Mechanical Problems –  Possibility of engine combustion leakage into the cooling system or symptoms of blown head gasket like engine oil in water or water in engine oil that shows a white milky appearance.

Understanding Your Engine Cooling System Operation

When the engine is running, a drive belt (fan belt) or timing belt powers the water pump. The water pump is designed to pump coolant around the engine.

While the engine is cold, the thermostat remains closed. This prevents coolant from going to the radiator. Instead, it circulates around inside the engine. This helps warm the engine quickly.

When the engine reaches operating temperature, the thermostat opens. The heated coolant then flows through the radiator. Excess coolant heat is transferred to the air flowing through the radiator. This maintains a proper engine operation.

Engine Coolant

Coolant performs several functions like preventing corrosion in the engine. If you live in colder climates there is a chemical called antifreeze which is added. The coolant colour can be pink, orange, blue, or green depending on the manufacturer. If the coolant is brown it usually indicates the cooling system needs flushing and the coolant replaced. There are coolant testers that can help you.

Tip: Keep your car’s engine cooling system clean by having it regularly flushed as per the manufacturer’s recommendation. This prevents the coolant from becoming contaminated and doing serious internal engine damage.

Engine Cooling Fan

Most later model vehicles are fitted with electric fans which use a heat-sensitive switch to turn the fan on to avoid engine overheating. If the engine is fitted with a Thermostatic fan clutch, the fan should slip when cold. When the engine warms, the clutch should engage. You should hear and feel air flowing through the radiator and over the engine.

Radiator

The radiator transfers coolant heat to the outside air. Cool outside air can flow freely through it. Look for any leaks around the top and bottom tanks. Also around the radiator drain plug. look at the overall condition and age of the radiator by looking for any damage to the fins.

Radiator Cap

The radiator cap performs several functions like sealing the cooling system. It also controls the pressure in the system which allows the boiling point of coolant in the system to be raised. If the pressure in the system is excessive it releases the pressure.

Check the rubber seal or O-ring condition to make sure the radiator cap is sealing.

Cooling System Hoses

Radiator hoses and heater hoses carry coolant between the engine water jackets and the radiator.  Look for leaking coolant before and after the test drive. Other symptoms of a bad radiator hose or may fail in the near future are:

  • Swolloen hoses or collapsed hoses due to age.
  • Deteriorated hoses due to oil contamination.

Thermostat

The thermostat helps to bring the engine to operating temperature more quickly from cold-starts. When the engine is at operating temperature the thermostat opens to allow the coolant to flow more freely through the radiator. When test driving the vehicle the engine operating temperature should be at a constant temperature.

Water Pump

Usually driven by the fan belt or the timing belt when the engine is running circulating the coolant (water) around and through the different cooling system parts and engine components. Worn shafts and bearings causing noise or leaks are common problems with an old water pump.

What to do If Your Car Overheats?

  1. Stop the vehicle in a safe place. Turn the air conditioning system off and turn on the heater.
  2. Check to see if there’s any steam or you hear a whooshing sound.

If there’s steam or noises: Stop the engine. Lift the hood after the steam goes away and the engine cools down then carefully check the coolant level and cooling system for any leaks.

If there’s no steam: Leave the engine running and lift the hood. Check the cooling fan is operating.

If you hear the cooling fan is operating: wait until the needle on the temperature gauge starts to fall and then stop the engine. Once the engine is cool you can check the coolant level for any leaks.

If you don’t hear the cooling fan operating: stop the engine. Then do the above checks once the engine has cooled down sufficiently.

Warning:

  • Wait until the steam has gone until opening the hood. The engine bay will be very hot.
  • Do not remove the radiator or reservoir cap if the engine is still hot. When removing use a rag or towel and open the cap gently with all parts of your skin and face away from harm.
  • When adding coolant (you can use water in an emergency situation) wait until the engine has cooled down. You don’t want to fill the cooling system with cold coolant or water to a hot engine quickly as this can cause damage to the engine.