By Owen Pham
There are many reasons why your car might overheat, even in winter. Yes, engines usually overheat during the warmer months and usually at the moment inconvenient times and places possible (see Charlie’s account of Nostalgia Super Stock), but it can happen all year.
A car overheating has to do more with the inner ecosystem of your vehicle than the temperature outside. The choices you make when your car first overheats determines the lifespan of both your engine and your wallet.
In this guide, we’ll go over the early signs of overheating issues, the first steps to take and possible diagnoses/solutions.
Why Is My Car Overheating?
Whenever your engine overheats, the main culprit is your cooling system. There are many components to your cooling system and they all have to work together to cool the engine. Sometimes, one small thing goes wrong and you can get away by limping on, but then comes a second issue, and now you are in serious trouble.
The first step to diagnosing an overheating engine is knowing how its cooling system works. Here below is a diagram of a cooling system.
Everything starts with the water pump. As the pump spins, it pushes the coolant towards the thermostat. The thermostat stays closed until the water warms it, and then it opens and allows the water to go through the upper radiator hose into the radiator. As it goes through the radiator, it’s cooled off by your fans (a clutch fan, an electric fan, or two eclectic fans).
Finally, it goes through your lower radiator hose back to your water pump. As the liquid heats up, it expands; some of it goes to your coolant recovery system or your reservoir. You also have a heater core, which helps to heat the inside of your car.
The causes of overheating are usually in one of these components. So it’s not that complicated, but it’s crucial to diagnose any problems. Sometimes, the solution is as simple as waiting for the car engine to cool down or to add coolant.
Signs That Your Engine Is Overheating
To spot an overheating engine, there are three signs you should look for;
- The temperature gauge in your dashboard is pointing at H or the red area.
- There is steam coming out from under the hood.
- The car smells strange. This is usually due to either an engine coolant leak (which would smell sweet) or an oil leak (which smells hot and causes smoke).
What to Do If My Engine Overheats?
- Turn off the air conditioning and blast the heater. Counter-intuitive? Yes. But this allows the heater to use the coolant to warm the air and acts as a mini-radiator. Just make sure to roll down the windows so you don’t overheat.
- Park or put your car in neutral and rev the engine. This will help your car cool down faster by allowing for more air and water circulation in the cooling system.
- Pop the hood, but carefully, because hot steam will likely blast out. We recommend wearing safety gloves from this step onwards.
- Wait at least 15 minutes for the engine temperature to cool down, then proceed to troubleshoot. Alternatively, simply have your car brought to the nearest auto repair shop by a tow truck.
How to Troubleshoot & Diagnose Overheating Causes
There are several steps to diagnosing a car that overheats. We’ll start from the basics (and the least expensive) to the more complicated and pricey problems.
1. Is Your Radiator Blocked by Debris?
Make sure your radiator is free of debris like leaves, sticks or mud. Remove them to allow free airflow into the radiator. And if you have mud on the radiator, hose it down.
2. Do You Have Enough Radiator Fluid and a Functional Coolant Container Cap?
After your car’s been cooling for 15 minutes, cover the coolant reservoir cap with a cloth and slowly loosen it a quarter at a time. This releases the pressure gently.
First, see if your cap is functioning. A functioning cap needs to hold a certain amount of pressure. If not, the resulting boiling can stall the cooling process. An effective cap should have some spring to it, and the rubber should still be there.
If your cap is no longer useful, you must replace it. Make sure to get one with the same pressure rating as the original cap; otherwise, it won’t be compatible with the rest of your system.
Once the cap’s off, see if there is any fluid in the container. If not, you’re running dry and need to top it off with a 50/50 antifreeze/distilled water solution. Add too much antifreeze and your car won’t cool, but add too much water and you’ll rust.
If your coolant container and your reservoir are full, make sure the fluid is clean. If the water has bits of metal in it, it could signal that your water pump is about to go out of order. In this case, refer to step 7.
3. Is Your Car Leaking?
Leaks are one of the major causes of cars overheating. To check for leaks, you have to pressure test the system, which requires certain tools. Many coolant pressure tester kits are available online. Plug the pressure tester onto the radiator, and pump up the pressure. At this point, you’ll probably see water leaking out of one of the components.
In more complex cases, if the pressure on the gauge drops on its own, you know there is a leak that needs to be fixed.
The main areas to check for leaks are:
- The radiator
- The core plugs
- The hose connections
- The thermostat housing
- The catch tank
- The water pump
If you don’t have a pressure test kit, look for the following signs:
- Drops in the radiator level
- An ever-rising temperature gauge
- Pools of coolant under the car
- Rust stains in the engine bay
4. Are There Air Bubbles in the Cooling System?
Air bubbles in the cooling system could be caused by anything from a recently replaced cooling system or a leak in the head gasket. Fix the most basic problem by burping the car according to the following steps:
- Park the vehicle uphill
- Make sure it’s cooled down
- Open the radiator cap and fill it with your 50/50 antifreeze and distilled water solution
- Start the car and let it get hot
- As it gets hot and the fluid levels drop, cap it off until it’s full. Repeat.
- Additionally, pinch your upper radiator hose on and off to dispel some of the bubbles.
5. Are the Fans Spinning?
Most cars have two fans, some only one. To test the fans, start your vehicle, crank your AC up, and see if it spins. Now, wait for the car to heat up. A working radiator fan should still spin when the car’s hot even if the AC is off.
Next, make sure it doesn’t wobble or makes excessive hissing. Also, check that the wires aren’t crossed because crossed wires mean the car is pushing instead of pulling the air through.
Sometimes, the fan motors have burnt out. To check for that, get jumper wires and stick one end on the positive cable of the battery while sticking the other on the red cable that feeds the motor. If the fan doesn’t start spinning, you’ll know the motor’s burnt out, and you need to replace it.
Your vehicle may also have a manual clutch fan. This is a fan with a thermostatic clutch that changes in spinning speed depending on the temperature. Although checking this fan is difficult and requires a trained experienced mechanic, you can still have a look yourself.
To test it, you’ll need to have someone start the car, watch the fan, and have them turn the car off. If it spins for more than 2 seconds after, you need to replace it. Also, you must have a fan shroud on.
6. Is Your Car’s Thermostat Functional?
A well-behaving thermostat should stay closed when the coolant is cold, and open when it’s warm. But if your thermostat is stuck and is closed, that’s a big reason for your car overheating.
To check it, touch the upper radiator hose, and if it’s consistently hot, you’re good to go. You can also check this with a cold engine if you open the radiator cap, start the car, and let it warm up. At this point, if your thermostat is working properly, you should see a noticeable drop in the fluid level.
7. Is Your Water Pump Working Properly?
If your water pump fails, it’ll cut the coolant circulation through the engine, and if left unattended will lead to further damage. Check your water pump while the engine is running, and if you see your pulley wobble, your bearings might be going out. As always, not hearing a strange noise is good. Again, if by revving the engine the water gets sucked down, your water pump is working properly.
If your coolant container and your reservoir aren’t empty, check to make sure the fluid is clean. If the water has bits of metal in it, then that could be a sign your water pump is about to malfunction. In such an event, the water pump blades will get cocked at an angle and will start shaving off the aluminium.
8. Do You Have a Blown Head Gasket?
If none of the above solves your problem, then you likely have a blown head gasket. This and a corroded radiator are two of the most problematic overheating causes because they require expensive repairs. That’s why we highly recommend seeing an experienced mechanic for this problem.
Why is My Car Smoking But Not Overheating?
Not a blown head gasket either? If they come into contact with a hot engine, all of the following can cause smoke without the car overheating:
- Gasket sealant material
- Engine cleaning products
- Faulty coolant flow
- Transmission fluid
This is commonly caused by leaks during filling or valve cover gasket leaks.
The Bottom Line
And there you have it—everything you need to know how to fix an overheating vehicle. Start from the basics (radiator fluid and air bubbles) to the more complicated parts (fans, leakage, thermostat, head gasket). Remember, the next time you wonder why your car overheats in the winter, don’t panic; get under the hood and fix it. Note that some models require a thorough investigation, so when you have time, always contact an expert.
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Author: Owen Pham
Muscle Car UK and Pilgrim Motorsports are leading UK classic car specialists for muscle cars, sports cars and classic cars. We build, service and upgrade all classic cars, specialising in Mustangs, V8 engines, Carroll Shelby Cobras and Corvettes.
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