5 Common Bad Thermostat Symptoms (Causes & Solutions)

Do you want to know the various Bad thermostat symptoms to look out for? if yes, Read on.

The car constantly overheating is not something any driver likes. All drivers are meant to know that a bad thermostat is one of the major reasons why a car would overheat.

Thermostats are simple and important components in a car’s engine. It controls coolant flow, which lets the engine maintain proper temperatures under different conditions.

Whenever the component fails, the thermostat is usually in what we know as the “stuck closed” or “stuck open” condition. In both cases (mostly the latter), damage to your engine might happen.

Your truck, van, utility vehicle, or car’s thermostat is also responsible for releasing coolants into the car’s engine immediately after it begins to heat up.

The temperature gauge could get bad after ten years, so for someone driving an older car, it’s always good to be aware of the signs your car would give if its thermostat starts having problems.

Below, we’ve given a guide that’ll help you understand how to identify common signs of a faulty thermostat, how to solve the problem of a faulty thermostat, and what it’ll cost you on average to get your thermostat replaced if it goes bad.

If you have a thermostat failure, it affects the functionality and operations of your car’s engine. Luckily, there are easily recognizable signs you’ll be able to notice whenever this occurs.

You’re to take the situation upon yourself and replace the thermostat immediately if you find out your thermostat is leaking or faulty. If this isn’t done immediately, your car’s engine can suffer irreversible damage. The longer the overheating, the worse the situation gets.

1. Temperature Gauge Reading Higher (or Lower) Than Normal

One of the common bad thermostat symptoms is a higher or lower than normal temp gauge reading. When you start your vehicle that has sat in a place for some time, the needle inside your temperature gauge is supposed to be on the gauge’s cool side.

As you drive, you will normally notice that the gauge will gradually creep until it gets to the gauge midway point, which is the engine’s optimal operating temperature.

In situations where it’s a stuck closed thermostat, it prevents the flow of coolant to the engine. So the gauge will keep rising until it is up to the gauge hot end.

If you keep driving your car at this point, you’re increasing the chance of damaging your engine, and the more you drive, the worse the situation gets.

This brings to the limelight the importance of always keeping your eyes on the engine’s temperature gauge. Immediately you notice that the temperature is going higher than it’s meant to, ensure to stop your car, so your engine can cool down.

Suppose it’s a situation where the thermostat is stuck open. In that case, you will notice the temperature needle moving up slower than it’s used to and possibly stopping before getting to the morning midpoint on the thermostat gauge.

When you take note of this, try cranking up your car heater, and when the air blowing out of your vent isn’t warm, it confirms that your thermostat is broken.

Also Read: Car Temperature Gauge Goes Up And Down While Driving (Causes and Solutions)

2. Coolant Leaks

Another common bad thermostat symptoms are coolant leaks. When there’s a thermostat failure, the thermostat remains closed. As a result, coolant overflows from a thermostat housing when an engine overheats.

This simply means that when coolants leak out of the engine, it can signal that the thermostat is bad. For example, it could signal something wrong with the radiator itself, radiator hoses, or gaskets and seals.

Bad Thermostat Symptoms

3. Increased Fuel Consumption

Increased fuel consumption is another common bad thermostat symptom. Engine overcooling and overheating can add largely to exhaust emissions and cause damage to fuel economy. It is so because the car will not be able to get to the temperature it’s to operate with.

In this scenario, signs of a thermostat failure will probably get translated into an increase in fuel consumption, resulting in an unexpected rise in the monthly utility bills.

4. Heater Malfunction

Another bad thermostat symptom is the heater malfunctioning. If you’re living in a cooler climate or driving in the middle of winter, you’ll possibly experience a temperature problem opposite in your car. Instead of the position being stuck closed, it’ll remain stuck open.

This means it’ll keep on allowing the flow of coolant into your engine, even if it does not need it. If you turn on your heater in the car cabin with an open thermostat, the HVAC vent will keep producing cool air, even when the heater temperature is turned up entirely. You’ll not get heat for you to warm yourself.

5. Rumbling Noises

You’d start hearing strange noises if the temperature changes weren’t bad enough. The noise will come from the engine, radiator, or both. This noise can also be like a boiling, gurgling, or knocking sound.

If you hear any of the strange noises described above while experiencing any of the signs listed here, it most certainly means that you’re having thermostat problems.

Also Read: Thermostat Housing Leak (Causes & Solutions)

How Does a Car Thermostat Work

Bad Thermostat Symptoms

A thermostat‘s main function is controlling the coolant going into the car’s engine. When you start your car that has been sitting for a while, its thermostat will close. This is because the engine gets hotter as you keep driving the car.

The thermostat opens up for coolants to flow through the car’s engine. This cools the engine and prevents the engine from overheating.

On the other hand, if you park your car somewhere and leave the engine running, the thermostat remains closed because it’ll take longer to get it to an operating temperature since it’s simply idling (compared to driving).

A thermostat that is functioning will know the right moment to open because of the coolant temperature sensor, which detects the operating temperature the engine is on currently. As you drive your car, the thermostat normally opens as the coolant consistently cools off the engine as it needs to.

This makes the engine retain normal temperature, which helps in maintaining its performance quality.

We equally have influences from the outside that can affect the engine temperature. An example is the temperature of our environment.

The hot and cold temperatures outside play important roles in the opening and closing of the thermostat. But as your thermostat is functional, it’ll know when it’s supposed to perform any of the tasks.

Where Is the Thermostat Located?

Bad Thermostat Symptoms

Often, it is located in metal or plastic housing near your water pump and connects to the lower hose of the radiator.

Most often, it’s located on a housing connecting the lower hose of the radiator, but in some vehicles, it could be the upper hose.

Because it’s often installed in a housing, in many cases, you can’t possibly see them with your eyes if they’re not removed. So using repair manuals is a very good way of finding your car model’s exact location.

What Is the Solution to a Bad Thermostat?

Once you’re certain that your thermostat is faulty or damaged, the best way to resolve the problem is by replacing the thermostat. You should always replace the thermostat with the same temperature rating as the vehicle’s repair manual.

We have several temperature ratings for thermostats; some could be very low as a hundred and sixty-five degrees or high up as two hundred and ten degrees.

Modern computer-controlled cars will have problems with their engine management if you make use of the wrong thermostat. When your car tries to fix whatever it thinks is a sign of a bad thermostat, the car might get the engine codes triggered or overheat.

Check out this video for more tips on how to fix a faulty thermostat

How Much Does It Cost to Replace a Car Thermostat?

Those with a faulty thermostat will find it relieving that replacing it doesn’t cost much. Notwithstanding, its exact cost depends on the model and make of your car. Nevertheless, an average driver should expect to spend between $140 to $300 for it to be replaced with the aid of a professional mechanic.

The main thermostat unit alone usually costs between $20 and $80, but it can increase for sports or luxury cars. The labor cost will be between $120 to $220 or more if you go to a dealership.

Some cars have a full house with their thermostat integrated, making it impossible for you to replace their thermostat alone. The cost could get very expensive because of this.

Some car thermostats are not placed well, requiring extra work hours, while others can be replaced within ten minutes, and you can do it yourself.

Find out the amount of work involved in replacing your car’s model thermostat in your repair manual.

Don’t forget that many mechanics charge around $80 to $110 per hour for their service. Replacing a thermostat would take about one to 2 hours for the mechanic to do the job completely. In the end, you’ll pay more for labor than the thermostat part itself.

Also Read: How Far Can You Drive An Overheating Car?

Frequently Asked Questions – Bad Thermostat Symptoms

Can I drive my car with a broken thermostat?

No. Even though your car might get you from one point to another physically, you’ll want to avoid driving it because it can damage more parts of the car, especially when there’s an overheating engine. You should take your car to the service center and get it fixed.

How can I test my car thermostat without removing it?

Start the engine and let it idle. Check if the coolant is flowing by looking through the neck of your radiator filer. At this point, it shouldn’t be flowing because your car hasn’t reached its operating temperature, and that’ll make your thermostat open. If the coolant flows, it means your thermostat’s valve is opened.

Can you fix a stuck closed thermostat?

It’s not advisable to repair your thermostat because you can’t trust it, and its failure can mean the engine has failed. If necessary, just remove it until you can install a replacement. Having a thermostat is necessary because a car’s computers require one hundred and ninety-two degrees for it to go into a closed loop.

What happens if your car thermostat is broken?

A broken thermostat results in unusual temperature changes when operating the engine. Here, the thermostat can’t be stuck in one position, and there’ll be readings that are false that’ll be causing control problems. The engine’s temperature will unpredictably change, and your radiator coolant won’t flow normally.

Could a faulty thermostat possibly cause a car to idle abnormally?

Yes, it can. If your thermostat gets stuck open, its engine might not reach the normal temperature it operates with, and the idling may become faster than usual. However, it will still idle smoothly unless there’s an added problem.

How much does it Cost to Replace a Car Thermostat?

The thermostat unit usually costs between$20 to $80, but the cost increases if it’s a sport or luxury car. The labor cost should be between $140 to $300 for you to get the replacement done by a professional mechanic.

Can a bad thermostat damage an engine?

When you have a damaged thermostat, your engine might not operate at an optimal temperature, making it overheat. This can damage your car’s engine seriously.

What happens if you run a car without a thermostat?

Driving your car with no thermostat will make it run at fifty degrees centigrade. Once your car is driving at this temperature, it’ll form humidity or moisture. And when it’s condensed, it mixes well with oil and then turns into watery ice (slush). This watery ice blocks lubrication out.

Conclusion – Bad Thermostat Symptoms

Many drivers try to save costs by doing the replacement labor themselves. However, if you don’t have good experience working on vehicles, or your car’s thermostat is easy to locate, your repair manual is good enough to direct you on what to do. It’s best to allow a professional mechanic to do the job of replacing the thermostat for you.

After all, your car might have other problems, and you’ll need a professional to diagnose these problems first before they go ahead to replace the thermostat.

Scott Greene is a seasoned automotive technician for over 5 years and has been deep into advanced automotive diagnostics for a couple of years. He Loves writing about Automotive Diagnostics and Repair, Trouble codes, Buyer guides for various car parts and accessories, and lots more. 

Leave a Comment