Stuck thermostat?

When driving the temp climbs between 210- 245. may bounce between the two temps. Doesn't drop when driving. Heater blows hot than cold. Heater has always blown hot.All these signs just started this morning. Is this a common sigh of a bad thermostat

My car has 218000 miles.
My car has an automatic transmission.

Experienced mechanics share their insights in answering this question :
From what you described, it potentially might be a few different things that may be wrong with your cooling system. As you may know, when the coolant is pumped through the radiator to the engine, some of this coolant is recirculated back through the heater core. Heated air from this is blown through the vents into the interior of your car. The fluctuation in temperature may be also caused by a faulty or stuck thermostat which may cause the erratic changes in temperature. This may also be caused by a clogged heater core or even heater core hose leaks. I would recommend having an expert from YourMechanic come to your home to diagnose and repair your cooling system.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

The most common reasons a Chevrolet Silverado 1500 heater isn`t working are a broken heater blower motor, a problem with the thermostat, or a failed heater blower motor resistor.
The most common reasons a Chevrolet Silverado 1500 is overheating are a coolant leak (water pump, radiator, hose etc.), the radiator fan, or a failed thermostat.
The most common reasons a Chevrolet Silverado 1500 ac isn`t working are a refrigerant leak, an electrical climate control issue, or a problem with the air conditioning compressor. You may not realize there`s a refrigerant leak until the air conditioner stops blowing cold.
Turn on the engine and feel the temperature of the coolant hose, but be cautious to not touch the engine. After ten minutes, feel the hose again. It should be slightly hotter. If it is not, then the thermostat housing is not opening.
If your coolant level is a-okay, but your car heater is blowing cold air and your engine is overheating, then you have a clog in your cooling system. Conversely, if your engine temperatures are unrealistically low after a drive, your thermostat is likely the culprit.
If the heater isn`t blowing hot air at you when you turn the system on, the blower fan might have a problem. Either it`s not getting electrical power or, more likely, the motor itself has simply burned out. A blower motor in an older vehicle is likely to burn out over time, and may need replacement.
Common Reasons AC Doesn`t Run Cold

The most common causes of broken air conditioning leaks or compression issues. If you are feeling cool — but not cold — air, the issue could be a clogged filter, a problem with the cooling fan, signs of radiator trouble, or it could simply mean it`s time to recharge your AC.

Look to see if the coolant is swirling/flowing immediately — that means the thermostat`s stuck open. If the coolant doesn`t flow after 10 minutes or so and continues to be stagnant after the temperature gauge indicates it`s hot, the thermostat`s likely stuck closed.
When a thermostat gets stuck open, it`ll allow coolant to circulate continuously even when it`s not needed. Unfortunately, that will overcool the engine and cause it to operate below its optimal temperature range. As a result, the engine will lose fuel efficiency, and its components will experience excess wear.
Causes of this can be not having enough coolant, a broken thermostat, a damaged heater core bypass valve, or a blockage in the core itself. If you encounter any of these issues, you should never drive an overheating car. Have it towed to an auto shop if you must, but you never want to risk your car`s engine.
A malfunctioning thermostat can make your heater or air conditioner unable to turn on. In most cases, this indicates the wiring has failed. Normally, electrical wires transmit messages from the thermostat to the HVAC unit, such as telling it when to turn on and what temperature to make your house feel.
One of the most common reasons why thermostats don`t work is dead batteries. If the batteries your the thermostat are dead, the thermostat will not be functional. Therefore, you will need to replace its batteries. If the thermostat still does not work after you do this, you may need to call a professional for help.
Key signs to look out for:

Weak or no airflow. Cold air (not warm) coming through the vents when the heater is on. Coolant leakage visible inside the cabin or a damp smell.

Key signs to look out for:

Weak or no airflow. Cold air (not warm) coming through the vents when the heater is on. Coolant leakage visible inside the cabin or a damp smell.

Causes of this can be not having enough coolant, a broken thermostat, a damaged heater core bypass valve, or a blockage in the core itself. If you encounter any of these issues, you should never drive an overheating car. Have it towed to an auto shop if you must, but you never want to risk your car`s engine.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

2003 jeep liberty stuck in reverse, shifter is stuck…but crawling under and trying to manually shift from transmission stuck
ANSWER : Hi there. Based on what you have written above, it is highly probable that the inner linkage has come loose or there is an obstruction within the inner gear set that is causing your problem. Unfortunately, this typically requires dropping the transmission and repair or inspection from the inside. This is not a service our mobile mechanics are equipped to offer, so your best bet is to contact a local transmission specialist for assistance.

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Car diagnoses says bad thermostat and shop said they had to replace the whole housing system as it isn’t separate
ANSWER : I have verified that the thermostat is only replaced with the housing since the housing and thermostat are built together and not sold or replaced separately.

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Shifter stuck in neutral. Brake pedal stuck. Wont go down. Car sat for 5 years. Rear manifold area very loud exhaust leak. Advice?
ANSWER : Hi there. If the vehicle has sat for an extended period of time, it is likely that multiple components; internal and external have ’frozen’ or have lost lubricity and are literally stuck. The clutch and transmission specifically can be negatively impacted due to lack of motion since it’s a hydraulic system, meaning it depends on consistent flow of fluid to maintain pressure in the system to work correctly. The brake pedal is also a hydraulic system – which is most likely why you’re having issues with this system. In regards to the helicopter sound, it is likely an exhaust manifold or exhaust pipe connection below the manifold that has cracked. However, since the Mitsubishi mechanics that apparently use stock exhaust manifolds on their "three times HP engines" said that’s impossible, maybe it’s best to take your car to them and have them put their skills to work to resolve your cars issues. To be honest, fixing the clutch, brake pedal and other systems that are stuck is going to be difficult and probably very expensive, so you might want to contact some other mechanics to get some estimates about repair costs before you get too deep into this project. Best of luck.

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engine light on for thermostat or temp sensor, EVIC falsely states engine hot due to bad thermostat, also service throttle control
ANSWER : Hello. From what you describe it would appear that your vehicle may be experiencing more than one issue. It is indeed true that the thermostat and coolant sensors are built into a housing, which will require replacement of the entire housing to replace the thermostat. The sensors can, however, be removed and reused. If there is a message displayed that the engine is overheating then that could signify that the coolant temperature sensor is bad, or that the engine is actually overheating, perhaps due to a stuck thermostat. Removing the thermostat does not require removal of the cylinder head, however it does require a few components be removed in order to access the housing. If there is a message also being displayed for the throttle control system, then it is likely that the computer has detected an issue that needs to be addressed. Perhaps a fault with the throttle body unit or circuit. As it appears that your vehicle may be experiencing more than one issue, I would recommend having a professional technician, such as one from YourMechanic, visit your location, to diagnose what may be causing the issues.

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we are trying to replace thermostat but manual is not showing the location of the thermostat and every videos shoe wrong engine
ANSWER : Trace the top radiator hose back to the engine. The top radiator hose will be connected to (or near) the thermostat housing. On the 2.0 engine, look for a plastic housing with multiple hose connections just to the left of the battery. You can request engine cooling thermostat and the responding certified mechanic will get this taken care of for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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My 03 745 li is over heating I changed thermostat and thermostat housing my car idols for five minutes and message comes on overhe
ANSWER : There may be trapped air in the cooling system. Air can get trapped if you drain coolant and then refill the system without purging. Trapped air can cause overheating by blocking coolant flow and can also faulty heater operation. Other common causes of overheating include low coolant level, a faulty thermostat, a plugged radiator, a faulty radiator pressure cap, collapsed hoses, non functioning cooling fans, and a faulty water pump or drive belt. Certain engine faults, such as a leaking head gasket, poor engine running condition, and exhaust blockages can also cause overheating. If you desire that this problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request an engine overheating diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

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How thermostat stuck open influences AC
ANSWER : Yes, because the computers control everything, and if the temperature isn’t right, it can often make the AC not work right. What you will also find is that the system has electric cooling fans.

If the car has a regular thermostat that opens and closes, it runs warmer and the fans will come on more. The more the fans come on, the better the AC is going to work. I would have a technician replace the thermostat first, as this is an inexpensive service that may fix all your problems.

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Low coolant temperature, thermostat issue
ANSWER : Hey there. If a new thermostat has been installed, I believe one of two things could be your issue. Either the thermostat you purchased is somehow faulty even as a brand new part or the cooling fan on your vehicle may be running at all times not allowing the engine to reach operating temperature. I would recommend taking the thermostat back and trying the repair again if your cooling fan is not running all the time. If the cooling fan is running all the time, you may have a short of some kind that is causing this to happen. In this case, the electrical system of your vehicle would need to be thoroughly inspected to determine where the source of the short is located. Due to the fact that thermostats are relatively inexpensive, the quality control on such a part is likely not very good. Therefore, a brand new thermostat may not be brand new quality. As long as the thermostat is not too difficult to access, I would recommend trying the thermostat replacement again. If you would like to have another mechanic take a look at this situation, a certified technician from YourMechanic can come to your home or office to inspect the cooling system and have this issue corrected.

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