8 Common Causes of Engine Overheating (and How to Locate the Source)
When your temperature gauge starts climbing into the red zone, panic can set in. But what’s really causing your engine to overheat?
While the reasons for an overheating engine are numerous, understanding them can help you quickly identify the source and prevent an inconvenience from becoming an expensive headache.
Related: 5 Signs That Your Car Is Overheating
Common Causes of Engine Overheating
There are quite a few potential reasons an engine can overheat. However, if you’re familiar with each of these causes, you may realize you’re more than capable of fixing this issue on your own.
Or at the very least, it will allow you to provide details to your local service center and possibly reducing your repair cost.
#1 – Low Coolant Level
A relative lack of coolant within a vehicle’s cooling system can quickly lead to engine overheating. This stems from the fact that reduced coolant flow robs an engine of its ability to exchange rising heat between its block and the vehicle’s radiator, thus leading to skyrocketing temperatures.
Under these circumstances, the source of a vehicle’s coolant loss should also be investigated as well as simply topping off coolant is likely only a temporary fix.
Related: Can You Add Water to Your Radiator in an Emergency?
#2 – Faulty Thermostat
A thermostat, when stuck in the closed position, can quickly lead to engine overheating. When a thermostat fails in the closed position, a blockage is effectively created within the cooling system, preventing flow between the radiator and engine itself.
When this occurs, overheating can occur in as little as 10 minutes of operation.
#3 – Water Pump Failure
A vehicle’s water pump is responsible for circulating coolant throughout the cooling system itself. A failed water pump, however, can prove incapable of sustaining sufficient coolant flow, thereby causing a vehicle’s engine to overheat in short order.
Under these circumstances, replacement of the faulty water pump will be necessitated.
#4 – Radiator Blockages
Another potential cause of engine overheating is radiator restrictions. When one or more blockages exist within a vehicle’s radiator, the flow of coolant within the cooling system is negatively impacted, often to the degree of causing significant overheating.
In most cases, the worse this restriction is, the more substantial the resulting overheating will be. One sign of a radiator blockage is a cold lower radiator hose.
#5 – Inoperable Radiator Fan
Most vehicles come equipped with specialized cooling fans that are designed to circulate additional air across the radiator itself, thereby promoting more efficient cooling. In some applications, these fans are strictly mechanical in nature, while other vehicles use electrically driven fans for this purpose.
In either event, a failed cooling fan can lead to engine overheating in short order, especially when sitting idle at a stop light.
#6 – Faulty Radiator Cap
Yet another potential cause of engine overheating is a faulty radiator cap. A vehicle’s radiator cap is engineered to prevent coolant loss under pressure, while also sustaining cooling system pressurization at sufficient levels.
Radiator cap failure will often allow cooling system pressure to bleed off prematurely, typically purging coolant from the system in the process.
#7 – Insufficient Engine Oil Levels
Excess friction within an engine can quickly result in a substantial build-up of heat. This often occurs when a vehicle’s engine oil levels drop below a permissible threshold.
The additional friction caused by inadequate lubrication of moving components yields noteworthy rises in temperature that even the most efficient cooling system cannot combat.
#8 – Blown Head Gasket and/or Intake Gasket
Though somewhat rare, in relation to a number of other potential causes on this list, a blown head gasket or intake gasket can also serve as a catalyst for engine overheating.
A failure at either point can lead to coolant consumption, or in the case of a faulty head gasket, even the mixing of coolant and engine oil. Both scenarios present cause for concern, in terms of cooling system efficiency.
Identifying the Source
Pinpointing the root cause of engine overheating often proves to be a multi-step process, involving thorough diagnostics, and a keen eye for detail. The following steps can be used to assist in diagnosing such issues, in a straightforward manner.
It is also advisable to consult a factory-specific service manual for your exact make and model of vehicle, before attempting any repairs of a rather involved nature.
Step 1 – Inspect Coolant Level
Begin by inspecting your vehicle’s coolant level to ensure that it is filled to capacity. If it is not filled to capacity, top off the system with coolant of the correct type/grade.
Additionally, verify that the coolant does not appear to be contaminated in any way.
Step 2 – Find Leaks (If Necessary)
If your vehicle’s coolant level was below its typical operating range during the above-mentioned inspection, the source of any offending leaks will need to be identified. This can often be done solely through visual inspection.
If no leaks are apparent, a cooling system pressure tester can be used to replicate difficult to locate leaks. Any leaks uncovered should be repaired immediately.
If system pressure loss is observed, but no external leaks are identified, additional qualification of the engine’s head gasket(s) intake gasket will be required.
Step 3 – Test Radiator Cap
Many cooling system pressure testers include special attachments for testing radiator caps. It is recommended to perform this test, to make sure that a defective radiator cap is not the source of your issues.
During this test, the cap itself should spring open to the bypass position at the exact pressure for which it is designed. If this does not occur, replacement is advised.
Step 4 – Check Engine Oil Levels
A quick check of the affected vehicle’s engine lubricating oil should also be conducted. Oil should be topped off at this point if it is not already.
Step 5 – Perform Operating Tests
Next, start your vehicle’s engine, and allow it several minutes to warm to operating temperature. With your vehicle’s engine at operating temperature, lightly squeeze the vehicle’s top radiator hose, confirming that both heat and pressure are present.
If this is not the case, suspect a faulty thermostat as a potential culprit.
Next, stand by and verify that the vehicle’s engine cooling fan activates at its specified temperature. If this does not occur, further inspection of the fan and its operating systems will be required.
Step 6 – Verify Sufficient Flow
If all other testing to this point has proven inconclusive, you should verify that flow within the cooling system is sufficient.
With the use of an infrared temperature gun, check for hot spots or points of restriction within the cooling system. Confirm that a noticeable reduction in temperature is evident across the radiator as well.
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I have problem with overheats of my truck which is Renault I have change the water pump, clean of radiator and I checked thermostat oil cooler, coolant is OK what is wrong now
It is possible to test a thermostat by throwing it in a pot of hot water (near boiling temperature) and see if it opens. If it doesn’t open, your thermostat might be bad.
When does it overheat? If the overheat happens at idle I’d check to make sure your radiator fans are kicking on. A bad fan, an unplugged fan, or a blown fuse could cause these fans to stop spinning which would lead to your truck overheating while it’s idling or moving slowly.
All was good until the radiator tank cracked. Replaced radiator, water pump and serpentine belt and thermostat. Now the car over heats after 10 mile drives. The lower radiator hose is cold and upper radiator hose is hot and it feels like it’s boiling inside.
Sounds like there’s some air left in the system. I would try to bleed the air out of the cooling system one more time. Make sure the radiator filler neck is the highest point, and run the vehicle until the thermostat opens. If you’re not sure how to do this, there are many great tutorials on YouTube.
My cars check engine light came on today. My car started to jerk and i noticed my car was running hot l. I got my oil changed when it happened. I got coolant and put some in my car because I noticed it was super low. My car is still running hot and jerking and I have no idea what the problem is I’ve experienced almost all of the things listed above
They also put my car on the computer at advance auto parts and it just told me something about my coolant system and he told me to buy coolant
Since your coolant was low, it’s possible you still have some air in the cooling system. I would get the cooling system bled of air and see if the problem persists. After bleeding the cooling system, check your coolant regularly. Top it up until your coolant level is at the full line.
My car is old but she has done me well the past 5 years, but the last 6 months I’ve been having issues where im having to fill my water every other day. Due to over heating it’s been serviced regularly has oil coolant all my heaters are blowing out cold air. Not to sure what to do?
Check to make sure you have no leaks in the cooling system. White streaks mean coolant is probably leaking near that location.
It may be worthwhile to do a leak down test. After overheating the vehicle, it is possible there is further engine damage. This could be a blown head gasket, warped heads, or a cracked block. A leak down test will tell you if you are losing compression through the cooling system or some other location.
I have been experiencing oil switch indicator flash light once my temp indicator rises up to 90 degrees and above, I just changed oil pump last 6 months ago due to the same oil switch lamp. This time the engine engine is experiencing difficulty in movement at 97 degrees centigrade. My vehicle is Opel 92 model with single injection fuel system.8 valves.Thanks.
Have you done an oil pressure test on the vehicle when it reaches that temperature?
Vw golf 2 litre. Engine heat’s up after every small trip and pushes out about 2 litre of water from the reservoir. I got the fan on direct using a switch. Still pushes out water After researching a bit. It seems like faulty thermostat
I would do a leak down test to see if perhaps it is a head gasket leak.
Why is my car making a gurgling sound when started
This is a common symptom of air in the heater core. You could try bleeding the air out of the cooling system, but I would also consider doing a leak down test to confirm if you have a head gasket leak.
My car doesn’t start, they say it has low compression, they say i must take it to the engineers (Renault Megan 1.6)
I have had engine overheating after flushing out the radiator,still I notice steaming hood,even when two fans attached to the radiator are in good working conditions.what could be the faults.
Make sure to bleed all the air out of the system any time you flush the radiator. Air pockets in the cooling system can often cause overheating issues. Some vehicles have a bleed valve to accomplish this, usually when the radiator filler neck is not the highest part of the cooling system.
If you’ve never done this before, look up a few guides online for the proper way to bleed your specific cooling system so you don’t risk burning yourself.