If your car is running hot but not overheating, it’s not something you should ignore. This usually indicates something is wrong with the cooling system and in severe cases, you might even be dealing with a blown head gasket. This can, understandably, be worrisome for most car owners, usually pointing towards expensive repairs. But before expecting the worst, you need to understand the many reasons behind the situation. By doing so, you can proceed by making informed decisions.
In this article, we walk you through the most common reasons a car is running hot but not overheating and what you need to do next. At the end, we finish off by answering your top questions. So, without further ado, let’s tackle this together!
8 Reasons Why Your Car Is Running Hot But Not Overheating
In most cars, the optimal operating temperature ranges from about 195 to 220 degrees Fahrenheit or 90 to 105 degrees Celsius. This means that if your car is running hot but not yet overheating, it’s still cooling, but just not enough, and thus, the temperature tends to be on the higher end of this range.
Listed below are the most common causes, starting with the most obvious:
- Overworked Engine
- Low Coolant
- Bad Thermostat
- Clogged or Bad Radiator
- Bad Temperature Sensors
- Bad Water Pump
- Blown head gasket
Overworked Engine
To be able first to cross off the most obvious reasons, let’s talk about an overworked engine. If the engine runs hot during specific situations, such as when towing a heavy load or climbing a hill with a vehicle full of cargo, it’s possible that you push the car too hard.
A contributing factor to this is if it’s hot outside and you run the air conditioner. In some cases, and even in stop-and-go traffic, this can cause too much stress and heat than the cooling system can handle. In turn, the engine temperature rises.
Low Coolant
Coolant, also known as antifreeze, circulates through the engine, absorbing heat and carrying it away to the radiator, where the radiator fan and aerodynamics cool it before being recirculated.
However, when the coolant level is low, there might not be enough fluid to absorb heat from the engine properly. In turn, this causes your car to run hotter than normal. But sometimes, there might still be enough coolant to absorb some of the heat and save your car from overheating.
Provided there’s no leak in the system, the good news is that if you simply have too little coolant, it’s a quick and easy solution. All you need to do is top it off with a compatible coolant. However, to be sure the existing coolant is efficient enough, I recommend flushing the whole system.
Bad Thermostat
So coolant circulates through the engine to absorb heat. But you don’t always want this. For example, when the engine is cold, such as at startup, you want the engine to reach a certain operating temperature quickly, right? Until then, it wouldn’t make sense to circulate the coolant.
So, what controls this flow of coolant? Enter the thermostat. Its job is to detect and regulate the engine’s temperature by opening and closing as needed to maintain an optimal temperature—neither too cold nor too hot.
However, when the thermostat goes bad, it fails to perform its job as intended. If it becomes stuck in the closed position, it will prevent coolant from flowing through the engine, causing the temperature to gradually creep up.
In some cases, it might still operate to some extent, allowing just enough coolant to pass through and prevent the engine from overheating. Nonetheless, it’s only a matter of time until it does.
Clogged or Bad Radiator
When the thermostat allows the coolant to flow through the system, it must go through the radiator to dissipate the absorbed heat. But if this rectangular or square-shaped radiator with narrow passages is clogged or bad, it can restrict the flow and reduce its ability to dissipate this heat effectively.
The culprits behind a clogged radiator are often old, contaminated coolant, or a buildup of rust and debris. Other times, some kind of impact can damage the radiator, making it less efficient. But in either case, you’ll likely see the temperature gauge rise, indicating that the engine is running hot.
Bad Temperature Sensors
There are various types of temperature sensors in your vehicle, including the coolant temperature sensor. Its job is to measure how hot the liquid becomes and communicate this to the Engine Control Module (ECM) or Engine Control Unit (ECU), allowing the computer to make adjustments to the air-fuel ratio since a cooler engine requires more fuel.
When the coolant temperature sensor malfunctions, it can send an incorrect “cold” signal to the ECM/ECU, tricking it into believing the engine isn’t hot yet, which causes the car to run hotter. In some cases, you might also experience rough idle and see black smoke from your exhaust pipes as the car is trying to burn too much fuel.
Additionally, if your car’s auxiliary fan relies on input from the coolant temperature sensor, it might stop working, which can also lead to a hot engine.
Bad Water Pump
The water pump is the heart of the cooling system, propelling the coolant through the engine and radiator. A malfunctioning water pump can bring the flow of coolant to a standstill or, at best, a meager trickle. This means your engine won’t get the cooling it needs, causing the temperature to escalate.
A tell-tale sign of a bad water pump is a coolant leak, but sometimes the pump’s impeller—the part that moves the coolant—may have disintegrated or broken off, preventing optimal flow without obvious external signs like leaking. Another symptom can be a squealing noise coming from the front of your car, often indicating a worn-out bearing in the water pump.
Blown head gasket
The head gasket forms a seal between the engine block and the cylinder head, which prevents oil and coolant from leaking into the cylinders. When the head gasket fails or starts to leak, it can give rise to a host of problems, one of which is causing the engine to overheat.
A compromised head gasket may allow coolant to leak out of the system or, even worse, mix with the engine oil. This weakens the lubricating properties of the oil and can result in additional damage to the engine.
If you suspect that your head gasket is blown, it is crucial to have it inspected without delay.
How to Fix a Car That’s Running Hot but Not Overheating
The first step to fix a car that is running hot is to figure out what’s wrong. Here’s what you need to do:
-
Read Trouble Codes
The first step is to plug in an OBD-II scanner and read the trouble codes stored in your car’s computer. This can offer valuable clues regarding what part might be malfunctioning, such as the thermostat. Make sure to note down any codes you encounter for further diagnostics or consultations with a professional mechanic.
-
Check The Coolant Level
Inspecting the coolant level is a straightforward task that anyone can do. When the engine is cool, open the hood, locate the coolant reservoir, and check if the fluid level falls between the “Min” and “Max” indicators.
If the coolant level is low, add a mixture of antifreeze and water—or a pre-mixed coolant—until it reaches the “Max” level. -
Flush and Bleed Coolant System
If it’s been a while since you had the coolant system flushed, it’s something I recommend you to do. Why? Old coolant can lose its anti-corrosive properties, leading to rust and scale accumulation that can clog your radiator. A flush and bleed will also clear out any air out of the system, ensuring efficient heat dissipation.
Here’s a guide on How to Flush and Bleed Coolant from thedrive.com
-
Measure The Coolant Temperature Sensor
If the trouble codes or your observations suggest that the coolant temperature sensor might be faulty, you can measure its resistance using a multimeter. The sensor is usually located close to or next to the thermostat.
This task might require some technical proficiency, so if you’re not comfortable doing it yourself, take your car to a professional. A malfunctioning sensor can skew the readings, making your cooling system work inefficiently.
-
Diagnose Thermostat and Coolant Flow
If the coolant seems fine and the temperature sensor is in working order, you may need to look at the thermostat. The simplest way to check if the thermostat is working is by feeling the upper radiator hose as the engine warms up. If the hose becomes hot, that means the thermostat has opened, and coolant is flowing. If it stays cool, your thermostat might be stuck closed, and replacing it would be the next step.
Note: Make sure you don’t burn yourself on hot engine parts.
-
Contact A Professional
If all else fails or you’re uncomfortable tackling these issues on your own, don’t hesitate to contact a professional. Overheating can lead to serious, often irreversible, damage to your engine. So, when in doubt, it’s better to seek professional advice.
By methodically running through these steps, you’ll be well on your way to pinpointing the issue. Each of these measures offers its own diagnostic insight into why your car might be running hot, enabling you to act before overheating becomes a reality. Remember, prevention is always better than cure, especially when it comes to your vehicle’s health.
FAQs
Why is my car running hot all of a sudden?
Your car might be running hot suddenly due to several reasons, such as a malfunctioning thermostat, a clogged radiator, or leaking coolant. Mechanical issues like a damaged water pump or a failing fan can also lead to overheating. Immediate diagnostic and repair are essential to avoid irreversible engine damage.
Why is my temperature gauge fluctuating but not overheating?
If your temperature gauge is fluctuating but not overheating, it could be due to a faulty or broken temperature gauge. Otherwise, it could be due to a bad temperature sensor, thermostat, clogged or damaged radiator and sometimes even a bad water pump. It’s important do diagnose the cause to avoid fruther damage.
Is it normal for a car to be hot after driving?
Yes, it’s normal for a car’s engine to be hot after driving, as long as it’s within a safe operating range—i.e., 195 to 220 degrees Fahrenheit or 90 to 105 degrees Celsius. If the heat seems excessive or the temperature gauge reads high, it may indicate a cooling system issue.
Should I worry about how hot my engine is running?
Yes, you should worry about how hot your engine is running, as overheating can cause serious damage to your engine. It can lead to warped cylinder heads, damaged pistons, and other costly repairs. If your temperature gauge is in the red zone or your engine is emitting smoke or steam, pull over immediately and let the engine cool down.
Why is my car running hot but not low on coolant?
If your car is running hot but not low on coolant, it could be due to a malfunctioning thermostat, a clogged radiator, or a damaged water pump. It could also be caused by a faulty temperature sensor or a leaking head gasket. It’s important to have your vehicle inspected by a professional to determine the root cause of the issue.
