20 Reasons Why Your Engine is Overheating

Twenty Reasons Why Your Engine is Overheating

In this Truck Radiator guide we are going to go over 20 reasons why your engine may be overheating. There are many causes of engine overheating and while we won’t go over all of them, we will point out some of the main causes of engine overheating and point you in the right direction for solving a overheating problem. Many of these cooling system problems are very simple to fixes that the average DIY person can perform, but some hard to detect and you will probably need a radiator repair shop to remedy. if you do not find the reason that you are overheating by performing these simple cooling system checks, then it might be time to visit your radiator repair shop.

1 – Your Thermostat Might be Stuck Closed or Open

A thermostat can cause engine overheating in many ways. It can be stuck shut, it can be stuck open, it can be partially open, it could be opening at the wrong temperature and it could just come apart and be broken. If you are overheating always check your thermostat, as it is one of the top causes of overheating.

2 – Engine Might have a Head Gasket leaking Coolant

A head gasket leak or cracked head or cylinder wall is a serious problem and needs to be addressed promptly. If you see bubbles in your cooling system it means compression is mixing with your antifreeze. Have your system checked for CO2 with a fluid tester. You can also take your radiator cap off and start the vehicle, if fluid jumps up out of the radiator you have a compression leak somewhere. Do not do this test with a hot vehicle and you may need to have a mechanic perform this test for you as many head gasket leaks are small and hard to just see with the naked eye.

3 – Paper, Dirt or Debris Blocking Radiator Airflow

Walk to the front of your vehicle and open your hood. Check to make sure there is not an obstruction blocking the grill, or the area between the grill and radiator. Common things are: plastic bags, cardboard, trash, cotton wood tree fluff, etc. If the grill or front of the radiator is obstructed, air cannot flow through the radiator and transfer the heat out of the antifreeze. Also, check between the condenser and the radiator as this tight spot can hold a lot of debris. A self-service car wash hose can clean out a lot of debris, just don’t get too close to the fins of the radiator and damage them or flatten them down.

4 – Electric Cooling Fan not Working or Fuse Blown

Your electric fan needs to turn on at certain times to keep your vehicle cool. The fan should turn on when your A/C is on, when the temperature rises to a certain point, when you shut off the vehicle but the engine is still too hot, etc. If your fan does not come on there are a number of things you will need to check. Start simple and make sure the fuse if good. If the fuse is ok you will need to check any sensors you have and then maybe your fan motor is bad or there is a wire short. In any case you must have your system checked when your electric fan is not working.

5 – Bad Water Pump is Leaking or Not Spinning the Impeller

A bad water pump can be hard to diagnose. Sometimes the propeller is worn or broken and since this is an internal issue you can’t see the problem. If you can’t find the reason you are overheating, then you will need to start looking at the water pump. Water pumps fail all the time but they don’t always leak and show an external sign of failure. A lot of the time the defect to a water pump is internal and only by removing the pump and checking it will you discover the water pump defect.

6 – Gasket Leaks can Occur in Many Places

Gasket leaks are normally easy to spot as you may see steam or dripping coolant. Sometimes a leak can come and go and as dirt and sludge moves around your cooling system. Sludge can actually act like a stop leak and plug up a small gasket leak. The problem is that it can also move out of that spot and a leak can start-up again. A few of the main spots to check for gasket leaks are the head gasket, the water pump gasket, and the thermostat housing gasket. Always check for current leaks and stains showing old leaks. Better to fix these gasket leaks before the leaks causes a highway breakdown.

7 – Removing Your Thermostat is a Bad Idea

This may sound strange to some, but removing your thermostat and letting the coolant run freely within your system can cause engine overheating. Why? When you allow coolant to race through your radiator it will not have the necessary time in the radiator to release the proper amount of heat. It is important that you slow down the coolant to a specific flow rate to allow for the proper dissipating of heat. Do not remove an old thermostat without replacing it with the proper temperature new thermostat.

8 – A Broken Fan Belt Will Drastically Cut Air Flow 

On vehicles with a belt driven fan, the belt can actually snap and fall off. A defective fan belt can cause the fan to stop working and not pull cooling air through the radiator.  If your on the highway you might not even notice this as the speed of your vehicle will push air through the radiator. Once you stop, that air will not be pushed through your cooling system and you will overheat. Always check your belt for wear and cracks and replace all rubber parts on schedule.

9 – A Defective Radiator Cap can Cause a Pressure Drop

A defective radiator cap will cause engine overheating in a number of ways. Three of the ways a radiator cap can cause overheating are, 1) Not holding in pressure and allowing the coolant to vent out or escape the cooling system.  2) No providing the proper pressure and not raising the boiling point. 3) Not releasing pressure when it reaches a certain point and allowing for too much pressure to build up and cause a system failure by bursting a hose, causing a radiator tank leak or radiator seam leak.

10 – If Your Radiator is Plugged Up You Will Lose Cooling Capacity

Radiators plug up for a number of reasons and while aluminum radiators don’t plug up as much as the copper radiators, they still can. The copper brass radiator can internally corrode and plug themselves up and a condition called solder bloom could cause the tubes to seal shut. Both copper brass and aluminum radiators can also plug up when you add too much stop leak, or while working on the engine you allow gasket material or dirt to enter the cooling system.  Any internal plugged up cooling system can be hard to diagnose but if you are overheating and can not see why, get your vehicle to a shop for testing, you may need to buy a new radiator.

11 – Low Coolant Level Can Mean You Have a Serious Problem 

A low coolant level is one of the easiest cooling system problems to find. You only have to visually check your reservoir coolant level or radiator, to see if your cooling system is low on coolant. You then just need to top it off to the proper level. The key here is to add the right mix of antifreeze and water and do not mix different antifreeze together. The next thing to check here is why is your cooling system leaking coolant. If this happens once and your refill holds then you probably do not have a problem and maybe just had a cooling system air pocket. But if the cooling system is loosing antifreeze over and over again then you have a radiator leak or a leak somewhere in the cooling system.

12 – A Bad Fan Clutch Will Spin but not Pull Air Through the Radiator

A fan clutch works by tightening up and pulling more air through the radiator as the cooling system heats up. A bad fan clutch will slip and not spin freely and thus not pull the air through the radiator dissipating the heat. To check a fan clutch just try to spin the fan while the cooling system is cold. If it the fan just spins freely then the clutch is bad. You can also look at the very center of the fan clutch, if you see an oil spot and dirt then the clutch is probably bad and will need to be replaced.

13 – Oil Leaking into a Cooling System Might be a Nightmare

If you find oil in the radiator you have a major problem. There are two types of oil that could leak into your cooling system, transmission oil and engine oil. Transmission oil can enter your cooling system if the transmission oil cooler that is inside your radiator leaks. You may also have engine oil in the radiator cause by a cracked engine head or cylinder wall. Both of these problems are very costly to fix and you will need to get your vehicle into the shop as soon as possible. You should not drive your vehicle if you have a transmission oil leak, an engine oil leak, or any oil mixed with your coolant.

14 – A Collapsing Radiator Hose Will Shut Down Your Cooling System

A collapsing radiator hose is usually caused by vacuum and is a sign of cooling system blockage or a bad radiator cap. A collapsing radiator hose will prevent coolant from moving through your cooling system and will quickly cause engine overheating.  A spring or coil is added inside some hoses to prevent the hose from collapsing and shutting off the coolant flow. Check all your hoses and make sure none are collapsed or sucked shut.

15 – A Broken or Missing Fan Shroud Will Cause Improper Air Flow

A fan shroud is an important part of your cooling system and needs to be attached while operating your vehicle. A Truck fan shroud helps funnel the air through the radiator and thus helps cool your engine. If your fan shroud breaks or cracks get it replaced as soon as possible to avoid overheating. Removing your fan shroud will cause engine overheating.

16 – Bad Hose Clamps Can Fail Causing a Highway Breakdown

A hose clamp can be weak and slip or pop off. It can also be cutting into your hose. Always check your hose clamps and feel under the clamp to make sure noting is seeping out of the hose. The cheapest hose clamp is not always the best buy and some of them do not hold properly. A clamp will last you a long time. Don’t buy the cheapest one you can find.

17 – Electrolysis Will Eat the Metal Within Your Cooling System

Electrolysis is caused by an electrical current being present in your cooling system and be very hard to diagnose. Electrolysis can be caused by loose or corroded ground straps or by old, worn out antifreeze allowing electrical current to flow through your cooling system. Electrolysis will eat away at your radiator, heater, water pump and all your metal parts and cause a cooling system failure from the inside out. If you think you have a problem have your system tested with a voltmeter.

18 – An Air Pocket Will Prevent the Cooling of Your Engine

Any time you lose coolant or you replace a cooling system part, you need to remove all the air that may become trapped in your cooling system. Air pockets are not visible, but it is easy to tell if you have one by double checking fluid levels and watching your gauge right after any cooling system work is performed. Air pockets can cause severe overheating and engine damage if left unchecked. You will need to “burp” a cooling system to remove any air pockets and open any bleeder valves your vehicle has to vent any air pockets stuck high up in your vehicle. Anytime you have work done on your vehicle or you replace your antifreeze you will need to check your coolant level at least once after the first time driving. Also, it is a good idea to keep your eye on the temperature gauge right after any cooling system work.

19 – A Radiator Leak Can Cause a Drop in Pressure and Coolant Levels

A radiator leak is very common and will cause a drop in coolant and engine overheating. Most leaks start  small and if you do the proper maintenance on your vehicle you should be able to spot potential weak spots before they get too bad. At times, a radiator will just pop and you will lose all your coolant in a matter of seconds. I have stood in front of my car with the hood up and the top tank just exploded off my radiator. Luckily, I was at my radiator repair shop and did not have to face a highway break down. Check your radiator during all oil changes and look up into the corners and the seams of the tanks and around hose connections. Most leaks start small as seeping leaks. Catching radiator leaks early will save you a lot of headaches, money and engine overheating.

20 – Radiator Hose Leaks are Very Common

We left one of the most obvious reason for engine overheating, radiator hose leaks, for last because almost everyone knows this reason. That said, just because you know it does not mean you will see it. Some hoses only leak at certain times and under pressure. Some hoses are cut into by the hose clamp and you may think the clamp is loose and just tighten it up, but that does not work. Check your hoses and the clamps. Look for soft spots, oil spots, rub marks and pin hole leaks. Change your hoses on schedule and save good old hoses in your trunk as highway spares. It may save you one day.

Engine Overheating Conclusion

While we have gone over a lot of reason your cooling system may be overheating, you must remember that we did not go over them all. We will touch base on other potential problems in a future article. Things like a bad exhaust system, vapor lock, needing a tune up, engine timing off, wrong antifreeze mix, too much antifreeze and not enough water, too much water, loose radiator fins, radiator external corrosion and fins falling out, condenser blockage, very high heat and traffic, pulling a heavy load and even more. Remember, if you do not see a simple reason for your engine overheating problem get your vehicle into the repair shop or your NARSA radiator repair shop as soon as possible.

engine overheating