A vehicle thermostat is a crucial component of the cooling system. It helps transport coolant from the radiator to the engine to maintain optimal engine operation.
It is a good practice to check your thermostat on every routine service to help regulate the coolant in the engine. The car thermostat relies on temperature changes to function properly.
For example, when you start your vehicle in the morning, the thermostat will not allow coolant to pass to the engine block until the engine reaches its normal operating temperature, permitting antifreeze to flow to the engine and radiator.
If the thermostat goes bad, it’ll restrict coolant flow, leading to an engine overheating. Engine overheating can cause a blown head gasket or catastrophic issues like swapped pistons, cracked blocks, or damaged cylinder heads.
You don’t want any of this to happen. Therefore, you need to test your thermostat regularly and ensure it works properly. This article will discuss how to test a car thermostat without removing it.
What is an Engine Thermostat?
An engine thermostat is a valve located between the engine and the radiator. Its primary function is to regulate the flow of coolant into the engine.
When the engine is cold, the thermostat remains closed, preventing coolant from flowing and allowing the engine to reach its optimal operating temperature more quickly.
Once the engine is warm, the thermostat opens and allows coolant to circulate, maintaining a stable temperature.
It’s usually at the end of the upper radiator hose and sits inside a housing bolted to the engine. A temperature-sensitive wax bead inside the thermostat expands or contracts, opening or closing the valve based on the coolant temperature.
Why is it important? It’s crucial for engine performance, fuel efficiency, and emissions control as the engine has an optimal temperature range for these factors.
Your thermostat might be failing if you notice:
- Overheating: If your engine suddenly spikes in temperature, it could be the result of a thermostat failure.
- Poor heater output: A thermostat stuck in the open position can cause the heater to blow cool air or not warm up sufficiently.
- Poor fuel mileage: Your car might start consuming more fuel than usual because the engine needs to run longer to reach the proper operating temperature.
- You fail a smog test: Excessive emissions can occur above and below the normal operating temperatures.
- Warning light on: It’s common for a Check Engine light to illuminate when the engine temperature is too high or too low.
If you suspect your thermostat is failing, it is important to address the issue promptly. Engine overheating can lead to severe damage, potentially causing extensive and expensive repairs.
How Does a Thermostat Work?
You may be wondering, “What does a car thermostat even do?” Most thermostats have a wax-filled brass tube that expands as the coolant gets hot, opening the thermostat’s valve against spring pressure.
A thermostat’s temperature rating represents the point at which the thermostat starts to open.
While the thermostat is closed, the coolant is pumped through the heater core or through a heater core bypass valve that only opens when cabin heat is requested.
When coolant temperature expands the wax pellet to open the valve, the coolant flows through the radiator to carry engine heat away so that the coolant returning to the engine is cool, and the thermostat closes again until the coolant gets hot enough to open it again.
You can actually watch this thermostat cycling happen if you graph the engine coolant temperature sensor on an idling engine.
The temperature at which the valve begins to open depends on the vehicle. Most late model thermostats open once the engine reaches 195 to 200 F. Once the engine shuts off and cools down, the wax contracts and closes the thermostat.
Where Are Thermostats Located?
Thermostats on cars are located in all different sorts of spots. What I personally do is start to look at each of the four corners of the engine. Imagine the engine is a cube, and look towards each corner for the thermostat housing.
In one of these corners the thermostat is usually residing. Very seldomly does the thermostat reside in the middle of the engine block somewhere, but sometimes it does happen. But the best way to find a thermostat is to follow the upper radiator hose.
The upper radiator hose is the hose that connects the car thermostat housing to the radiator. Usually, it’s the largest hose you can see in the engine bay. The hose is usually located in front of the engine and it’s attached to the radiator.
If you follow the radiator hose from the radiator to the engine block, you will find the thermostat.
The junction where the engine block and the radiator hose meet is where you will find the thermostat. So when in doubt, just follow the radiator hose from the radiator, to the engine block, and you will find the thermostat housing, and in turn, the thermostat.
How Can I Test My Thermostat Without Removing It?
Testing your thermostat without taking it out is possible and can save you a lot of time and effort. The key is to observe how your engine and cooling system behave as the engine heats up. We’ll focus on checking coolant flow and temperature.
#1. Checking Coolant Flow in the Radiator.
This is one of the most effective ways to see if your thermostat is opening. You’ll need to let your engine warm up, so safety first!
What You’ll Need
- Gloves
- Safety glasses
- A rag
- Patience
Steps
- Start the Engine: Turn on your car and let the engine idle.
- Allow Engine to Warm Up: This is the crucial part. You need to give the engine enough time to reach its normal operating temperature. This can take anywhere from 10 to 20 minutes, depending on the weather and your car. Keep an eye on your temperature gauge.
- Carefully Feel the Radiator Hoses: Once the engine is warm and the temperature gauge is nearing the normal range, you’ll want to feel the upper and lower radiator hoses. Be very careful, as these parts can get extremely hot. Use a rag to protect your hand.
- What to Look For:
- Upper Radiator Hose Gets Hot: As the engine heats up, the upper hose, which carries hot coolant from the engine to the radiator, should become hot. This indicates that the engine is producing heat.
- Lower Radiator Hose Stays Cool or Lukewarm (Initially): The lower hose carries cooler coolant from the radiator back to the engine. Initially, while the thermostat is closed, this hose should remain relatively cool.
- Lower Radiator Hose Gets Hot (When Thermostat Opens): This is the tell-tale sign. Once the engine reaches its operating temperature and the thermostat is supposed to open, the lower radiator hose will also become hot. This means coolant is now flowing through the radiator.
- What If It Doesn’t Get Hot? If the upper hose gets hot, but the lower hose stays cool even when the engine is at operating temperature, your thermostat is likely stuck closed. This prevents hot coolant from circulating to the radiator for cooling.
#2. Observing the Temperature Gauge.
Your car’s temperature gauge is your first line of defense and can give you clues without touching anything hot.
- Normal Range: Most cars have a needle that sits in the middle of the gauge when the engine is at its ideal operating temperature.
- Climbing Too Fast or Staying Too Low: As mentioned, if the needle quickly goes to the red, or if it never moves much from the cold end, it points to a thermostat problem.
#3. Checking for Coolant Leaks.
While not a direct test of the thermostat itself, coolant leaks can often be associated with thermostat housing issues or general cooling system problems that might be mistaken for a thermostat failure.
- Visual Inspection: Look around the engine bay for any puddles of colored liquid (coolant is usually green, orange, or pink). Pay close attention to the area around the thermostat housing.
- Smell: A sweet, often syrupy smell can indicate a coolant leak.
#4. Using an Infrared Thermometer (Advanced Option).
If you have access to an infrared thermometer, you can get more precise temperature readings. This tool allows you to measure surface temperatures without touching anything.
Steps
- Warm Up the Engine: Let your car run until it reaches its normal operating temperature.
- Measure Radiator Hoses: Point the infrared thermometer at the upper radiator hose and then the lower radiator hose.
- Compare Temperatures:
- When the thermostat is working correctly, the upper hose should be significantly hotter than the lower hose once the engine is fully warmed up.
- If the temperatures are very similar, or if the lower hose isn’t getting warmer as expected, the thermostat might be stuck open or closed.
This method requires knowing what normal temperature differences should be for your specific car, so it’s often used by those with a bit more automotive experience.
What happens if a thermostat is stuck closed?
Normally, a vehicle thermostat remains closed when you start a vehicle until it reaches the normal operating temperature.
This means it will not allow coolant to flow from the radiator to the engine. However, once the engine reaches its full operating temp, it’ll open and grant coolant passage to cool the engine.
However, if the thermostat is stuck closed, it’ll prevent coolant passage even when the engine is extremely hot. If you have a stuck closed thermostat, the upper and lower radiator hose will be cool even when the engine is overheating.
The upper and lower radiator hoses should be hot when an engine reaches normal operating temperature. In any case, the upper Hose should be hotter than the lower hose. You have a stuck closed thermostat if the radiator hoses are cool after a 5-15 minute run.
Understanding Thermostat Failure Modes
Thermostats can fail in a couple of main ways, and knowing them helps you interpret your tests.
Stuck Closed
This is when the thermostat’s valve remains shut even when the engine is hot. Coolant can’t reach the radiator, leading to rapid overheating. This is why the upper hose gets hot, but the lower hose stays cool, and the engine temperature soars.
Stuck Open
In this case, the thermostat valve stays open. Coolant constantly circulates through the radiator, even when the engine is cold. This prevents the engine from reaching its optimal operating temperature.
You’ll notice the temperature gauge staying low, and the engine might run rough or have poor fuel efficiency. In this scenario, both hoses might feel similarly warm, but the engine never reaches its normal heat.
Troubleshooting Thermostat Issues
If your thermostat test indicates a problem, here are some troubleshooting steps:
- Replace the thermostat: If the thermostat is faulty, it should be replaced.
- Check the coolant level: Ensure the coolant level is adequate.
- Inspect the water pump: A faulty water pump can affect coolant flow.
- Check for air pockets: Air pockets in the cooling system can interfere with thermostat operation.
- Consider a professional diagnosis: If the problem persists, seek professional assistance from a mechanic.
Step-by-Step Guide to Testing the Thermostat
Testing your car’s thermostat without removing it is simpler than you might think. Follow these easy steps to ensure your engine’s temperature stays just right:
#1. Park the Car and Let the Engine Cool Down.
Before starting any work under the hood, make sure your car is parked on a level surface. Give the engine plenty of time to cool down to avoid burns from hot components.
#2. Locate the Thermostat Housing.
The thermostat is usually located between the engine and the radiator. Refer to your car’s owner’s manual if you’re unsure where to find it.
Once located, identify the thermostat housing, which is typically attached to the engine and connected to the upper radiator hose.
#3. Test the Thermostat Using a Coolant Tester.
- Remove the Radiator or Reservoir Cap: Be cautious as the coolant system might still be pressurized. Use a rag or glove to protect your hand while carefully loosening the cap.
- Insert the Coolant Tester into the Coolant: Follow the manufacturer’s instructions for your specific coolant tester. Typically, you’ll insert the tester into the coolant reservoir or radiator opening.
- Pump the Tester and Observe the Pressure Reading: Pump the tester to increase pressure within the cooling system. Keep an eye on the pressure gauge and compare the reading to the specifications provided in your owner’s manual. If the pressure does not reach the specified range, it could indicate a faulty thermostat.
#4. Test the Thermostat Using a Multimeter (if Applicable).
- Set the Multimeter to the Resistance or Ohms Setting: Ensure the multimeter is set to measure electrical resistance, often denoted by the symbol Ω or “Ohms.”
- Remove the Thermostat from the Housing: Carefully detach the thermostat from its housing. Refer to your owner’s manual for guidance if needed.
- Connect the Multimeter Leads to the Thermostat Terminals: Touch one multimeter leading to each of the thermostat’s terminals. The multimeter should display a resistance reading.
- Check the Resistance Reading Against the Specified Range: Consult your owner’s manual for the recommended resistance range. If the resistance reading falls outside of this range, it suggests a malfunctioning thermostat.
#5. Interpret the Results and Determine the Next Steps.
After completing both tests, carefully interpret the results. If either test indicates a faulty thermostat, it’s essential to replace it promptly to prevent engine damage and maintain optimal performance.
By following these straightforward steps, you can confidently test your car’s thermostat without the need for removal, ensuring your engine stays cool and runs smoothly on the road ahead.
Pros of Removing the Thermostat
There are a few advantages of removing the thermostat.
#1. Improved Engine Cooling.
When you remove the thermostat, coolant flows freely through the engine at all times. This ensures a constant and consistent cooling effect, especially during hot weather or demanding driving conditions.
Without the restriction imposed by the thermostat, the engine can maintain a lower and more stable operating temperature.
This can be particularly advantageous for high-performance vehicles or those used for towing heavy loads, as it helps prevent overheating and potential engine damage.
#2. Enhanced Engine Performance.
Some car enthusiasts believe that removing the thermostat can improve engine performance. The rationale behind this idea is that by allowing the coolant to flow freely, the engine can reach its optimal operating temperature more quickly.
This can result in improved combustion efficiency, better fuel economy, and potentially increased horsepower. However, it’s important to note that the impact on performance may vary depending on the specific vehicle and its design.
#3. Simplicity.
The removal of the thermostat simplifies the cooling system by eliminating one component. This can reduce the complexity of the system and potentially make it easier to diagnose and repair any cooling-related issues.
#4. Cost Savings.
Over time, thermostats can wear out or become faulty, requiring replacement. By removing the thermostat, you eliminate the need for this specific part and its associated maintenance costs.
While the cost savings may not be substantial, it can be a consideration for those on a tight budget or looking for ways to minimize maintenance expenses.
Cons of Removing the Thermostat
On the other hand, there are several downsides to removing the thermostat.
#1. Error Codes.
Modern vehicles come equipped with a variety of sensors, one of which monitors coolant temperature.
If the vehicle’s computer detects that the engine is not reaching its proper operating temperature, it might trigger a Check Engine light, which could cause your vehicle to fail an emissions test or mask other potentially serious engine issues.
#2. Potential Engine Damage.
Operating an engine too cold can be just as damaging as running it too hot. Engines are designed to run at a specific temperature.
When running cold, the engine’s fuel and air mixture can run rich, leading to incomplete combustion, which can cause carbon build-up and potential damage to components such as spark plugs and the catalytic converter.
#3. Increased Fuel Consumption.
Cars are designed to run most efficiently at specific temperatures. If your engine never reaches this temperature, it can lead to increased fuel consumption, as the engine’s computer may enrich the fuel mixture in response to the colder operating temperature.
#4. Reduced Heater Performance.
The thermostat plays a vital role in regulating coolant flow to the heater core, which provides heat for the interior of the vehicle. By removing the thermostat, the coolant circulates continuously, and the heater may not reach its optimal temperature.
This can result in reduced heating performance and slower warm-up times during cold weather, making it uncomfortable for passengers and potentially affecting defrosting capabilities.
#5. Inconsistent Engine Performance.
The thermostat helps maintain a consistent engine temperature, which is crucial for optimal engine performance.
Without the thermostat, the engine may struggle to reach its ideal operating temperature, resulting in reduced power, lower fuel efficiency, and potential drivability issues.
Inconsistent engine performance can affect the overall driving experience and lead to increased wear and tear on engine components.
#6. Warranty and Insurance Issues.
Modifying your vehicle’s cooling system by removing the thermostat may void your vehicle’s warranty, especially if any related issues arise. Additionally, some insurance policies have specific requirements regarding modifications made to the vehicle.
Removing the thermostat could affect your coverage or result in denied claims in the event of engine damage or other cooling system-related issues.
#7. Environmental Impact.
Operating the engine at a lower temperature consistently due to the absence of a thermostat can increase emissions, as the engine’s control systems may not be able to optimize fuel combustion efficiency.
This can contribute to higher levels of pollutants being released into the atmosphere, negatively impacting air quality and the environment.
FAQs.
Q: Can you run a car without a thermostat in the summer?
Yes, you can drive a car without a thermostat in both summer and winter. The primary function of a thermostat is to allow coolant passage when the engine gets to 185 degrees Fahrenheit.
Without the thermostat, there will be constant coolant flow from the radiator to the engine.
In any case, driving without a thermostat is not ideal here in the United States. In some African countries, the service technicians don’t replace thermostats once it goes bad.
You’ll enjoy the benefits of removing a thermostat (which is a no-closed position) if you drive without this component.
Q: Why is my car overheating with a new thermostat?
Several factors can cause a car to overheat. So, suppose your vehicle is overheating with a new thermostat. It could be you have a bad water pump, bad radiator, lousy cooling fan, clogged heater core, or any cooling system-related issues.
If your new thermostat is not opening, it could be that you didn’t install it properly. The most important thing to do is park the vehicle in your garage until you fix the problem. If you ignore and continue driving with it, it can escalate and cause catastrophic damage.
Q: Can you drive with a thermostat stuck open?
While a stuck closed thermostat can cause engine overheating, leading to a catastrophic breakdown if you fail to fix it on time, you can drive thousands of miles with a stuck open thermostat.
However, you may experience some issues along the way. It is expected for coolant to continue circulating coolant from the radiator to the engine and back when the engine is working at an average temperature.
This circulation process poses a problem when the engine is cold. The ECM will keep the engine on a warm cycle to get the engine to a higher operating temp, burning more fuel. In any case, the amount of extra fuel burnt can be as little as insignificant.
Final Words
A car thermostat can fail because of dirt, debris, or high-temperature differences. The common symptoms you’ll notice are overheating engine warning lights and coolant leaks.
I recommend you check out this article – Coolant Temperature Reading; what’s Normal and what’s Not.
So, if your engine overheats and you suspect a lousy thermostat to be the culprit, inspect the component. Thankfully, you can test a car thermostat without removing it.
Scroll up to the simplified guide above and follow the instructions to check your thermostat.