Rick's Free Auto Repair Advice

What causes engine overheating

Six most common causes of engine overheating

Here are the six most common causes of engine overheating

  • Radiator fan not working
  • Faulty thermostat
  • Burst hose or leaking radiator or water pump that causes Low coolant
  • Faulty water pump
  • Clogged radiator
  • Damaged head gasket

What goes wrong with radiator fans?

Most late model vehicles have several electric radiator Radiator fan motor, blade, and shroud for Ford Mercuryfans that run at different speeds depending on the cooling needs of the engine. GM, for example uses two fans that can run at two speeds. If you’re driving with your AC on, the fans run at high speed at all times. With the AC off, the engine computer determines whether to run the fans at low or high speeds depending on how well the low speed is removing heat. The most common cause of GM radiator fan failure is a bad rely. There are three relays, so check all three. Here’s a link to how to check them.

Chrysler uses a different method. Their electric radiator fan relays run the fan at variable speeds depending on how much cooling is required. A failed radiator fan relay is the most common cause of engine overheating. See this post on how to diagnose and fix a Chrysler radiator fan relay.

Other car makers use variations on those two approaches, where relays control the fan speed or a variable type relay is used to provide varying fan speeds based on cooling needs.

cheverolet avalanche thermostat

Engine Thermostat

Engine thermostats operate with a wax pellet that melts at higher engine temperatures. The wax expands as it melt and forces a pin outward that open a valve, allowing coolant to flow. Over time, the rubber sealing gasket wears out and the molten wax seeps into the coolant. At that point, the thermostat stops working, leaving it in a permanently closed position. In other words, there’s no coolant flow and your engine overheats.

What causes a radiator hose to burst?

The most likely cause is old age. Radiator hoses are coolant coating on hoseunder constant pressure and over time the rubber deteriorates. That’s why you should check the condition of your hoses regularly, especially on an older car.

What causes a water pump to fail?

I’ve seen water pumps last for 300K miles and I’ve seen them fail at 100K miles. What’s makes the difference? Simple. Neglecting coolant changes or using the wrong coolant is the single best way to damage your water pump. See this post on water pumps and see this post on coolants.

What causes a clogged radiator?

Neglecting coolant changes or using the wrong coolant is

clogged car radiator

Corroded radiator tubes

the main reason for clogged radiator passages.

What causes a head gasket to fail?

Neglect and engine overheating. Neglecting coolant changes allows corrosion to set in and that corrosion builds up in coolant passages, restricting coolant flow and causing engine overheating that can damage the head gasket. Neglecting oil changes causes the oil to build up excessive amounts of acid that attacks gasket materials.

head gasket leak

Typical head gasket


A failed radiator fan or relay or a faulty water pump that allows the engine to overheat can cause a head gasket to fail.

©, 2017 Rick Muscoplat





Posted on by Rick Muscoplat

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