We get a lot of calls asking “why is my engine overheating?”  Over time we have compiled a short list of common Causes of Engine Overheating.  We add to this list from time to time so check back as needed.

Stuck Thermostats Cause Engine Overheating

Your thermostat is usually located in a housing where the upper radiator hose connects to the engine.  It controls the operating temperature of the engine by blocking the flow of coolant from the engine to the radiator until the engine reaches the desired temperature.  When the thermostat opens coolant is permitted to circulate from the engine to the radiator. Unfortunately if the thermostat sticks usually caused by a steam pocket under the thermostat due to incomplete filling of the cooling system or coolant loss in the system, no coolant can circulate through the radiator and engine overheat (quickly). You can check for a stuck thermostat by carefully touching the upper radiator hose when the engine is first started and is warming up.  (Watch out for spinning fans blades). If the upper radiator hose fails to get become hot to the touch within a few minutes of starting the engine, the thermostat may be defective and needs to be replacement.

Defective Fan Clutches Cause Engine Overheating

A fan clutch is often used to improve fuel economy on rear wheel drive vehicles with mechanical i.e. belt driven fans.  The clutch is a viscous-coupling filled with silicone oil that lets the fan slip at high speed and reduces the parasitic horsepower drag on the engine. If the clutch slips too much though the fan cannot turn fast enough to circulate the air and cool the engine. Over time that silicone fluid inside the clutch breaks down and may leak out. If you see oil streaks radiating outward on the clutch or the fan can free spin the fan with your hand (when the engine is off!) the clutch may be compromised and need replacement.  Play or wobble in the fan due to wear in the clutch also signals the need for a new clutch and will destroy you water pump bearings.

Electric Fan Motor Failures Cause Engine Overheating

A temperature switch or coolant sensor in the cooling system cycles the electric fna used on many front-wheel drive cars.  A failure in the  temperature switch,  coolant sensor or the relay that send power to the 12V fan motor will lead to engine overheating.  If the fan motor itself goes bad, the fan won't work and you the limited airflow will also result in engine overheating.

Coolant Leaks Cause Engine Overheating

Loss of coolant in the cooling system due to leaks in the radiator, heater hoses, water pump, heater core or engine freeze plugs will reduce the coolant levels and result in rapid overheating. A flashlight and a keen eye will help isolate the leak.

Radiator Caps can Cause Engine Overheating

If you cannot find the leak but still experience coolant  you may want to check the radiator cap under pressure tested.  A week spring inside the will cause coolant loss through the out the overflow or expansion tank.

Internal Coolant Leaks Cause Engine Overheating

Still can’t find the leak then brace yourself as there may be a crack in the cylinder head or block, or a leaky head gasket allowing coolant to escape into the combustion chamber or crankcase.   This is bad news.

Clogged Radiators Cause Engine Overheating

Clogged radiators and heater cores can impede coolant flow rates and create hot spots in the core.  This reduced cooling capacity will result in overheating as the radiator cannot fully dissipate the engine heat.

Exhaust Restriction Causes Engine Overheating

If you have restricted the exhaust resulting in back pressure you can cause your engine. Blockage may be in a plugged catalytic converter or compressed pipe. Test your intake vacuum and exhaust back pressure to rule this out

Failed Water Pumps Cause Engine Overheating

Not maintaining your coolant system pH can corrode an aluminum or steel water pump impeller to the point that blades eaten away. You must replace your water pump. Other common pump failure is the pump shaft, bearing or seal.  The water pump is a mechanical part in a corrosive environment and the bearings and seals eventually wear out.  Coolant leaking past the shaft seal will limit system capacity and result in overheating.