Tip & How-To about Heating & Cooling

How a thermostat works

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The thermostat's main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. At low temperatures, the outlet to the radiator is completely blocked -- all of the coolant is recirculated back through the engine.
Once the temperature of the coolant rises to between 180 and 195 F (82 - 91 C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200 to 218 F (93 - 103 C), the thermostat is open all the way.
If you ever have the chance to test one, a thermostat is an amazing thing to watch because what it does seems impossible. You can put one in a pot of boiling water on the stove. As it heats up, its valve opens about an inch, apparently by magic! If you'd like to try this yourself, go to a car parts store and buy one for a couple of bucks.
The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at around 180 F (different thermostats open at different temperatures, but 180 F is a common one). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly, pushing the rod out of the cylinder and opening the valve. If you have read How Thermometers Work and done the experiment with the bottle and the straw, you have seen this process in action -- the wax just expands a good bit more because it is changing from a solid to a liquid in addition to expanding from the heat.
This same technique is used in automatic openers for greenhouse vents and skylights. In these devices, the wax melts at a lower temperature.
Fan Cooling fan
­L­ike the thermostat, the cooling fan has to be controlled so that it allows the engine to maintain a constant temperature.
Front-wheel drive cars have electric fans because the engine is usually mounted transversely, meaning the output of the engine points toward the side of the car. The fans are controlled either with a thermostatic switch or by the engine computer, and they turn on when the temperature of the coolant goes above a set point. They turn back off when the temperature drops below that point.
Rear-wheel drive cars with longitudinal engines usually have engine-driven cooling fans. These fans have a thermostatically controlled viscous clutch. This clutch is positioned at the hub of the fan, in the airflow coming through the radiator. This special viscous clutch is much like the viscous coupling sometimes found in all-wheel drive cars.

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1 Answer

How many thermostats are there


There is only one thermostat that I know for any engine. This valve controls the circulation of water from the radiator into the engine for controlled temperature operation.

During cold engine start-up the thermostat remains closed to allow the engine to heat up quickly. When the engine reaches operating temperature the thermostat opens and closes to maintain a predetermined temperature as defined by the specif part.

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Feb 28, 2016 | Cars & Trucks

1 Answer

i have a 2005 impala it blows cold air only.the thermostate is set at the hottest setting.i dont think its the heater core because it does not overheat and its not leaking antifreeze.what could it be?


It's more than likely the thermostat. If you have a 3800 V6 this is a very quick and easy fix. It you have a 3400 engine, this can be a pretty frustrating job. The bolts that hold the thermostat housing on are very difficult to get at on a 3400 engine. Either way, the thermostat itself is only $10-$12.

If your thermostat is stuck open the engine coolant will constantly circulate and won't warm up to normal operating temperature. Since it isn't warming up, you won't have any heat inside either.

Nov 06, 2010 | 2005 Chevrolet Impala

2 Answers

heat blow cold air


most likely a problem with the water circulation around the heater core. if you've never used the heater, some vehicles have a hot water shut-off valve for the heater hoses. another possibility is the thermostat had been removed. the easiest way is to start the vehicle and slowly allow it to warm up monitoring the water temperature. it should heat up to normal water temperature, then heat up and then drop down. the thermostat is usually around 180 degrees or 192 degrees. it allows the water around the engine block to heat up then once it reaches 180 or whatever it opens up circulating the cooler water from the radiator into the engine block and pushing the hotter water into the radiator to cool off. no thermostat, then the water keeps constantly circulating not allowing it to properly heat up. this can slow the heater down, lower fuel economy, alot of things especially in the winter driving...

Oct 03, 2009 | 2001 Ford Focus

1 Answer

2005 dodge caravan need to know symptoms for faulty thermostat


There are two primary symptoms of a faulty thermostat (assuming you mean the coolant thermostat in the engine not the A/C Heater Thermostat).  The thermostat can fail in basically two ways:
1)  Stuck open - Engine runs colder, heater takes forever to heat up. 2)  Stuck closed - Engine runs very hot, then will suddenly drop in temperature, then run very hot again.  Or engine overheats constantly.  When the engine is hot, feel the upper radiator hose.  If it is not hot, you can bet the thermostat is stuck closed.  If it is hot, the thermostat may not be stuck close, but not opening at the proper temperature.
Stuck open is annoying, but not dangerous.  Stuck close is dangerous and can cause overheating-related damage to your engine.
If you are handy, you can replace it yourself.  Otherwise it is an easy job for a mechanic.

Jan 24, 2009 | 2005 Dodge Caravan

1 Answer

97 Ford Taurus


Replace the engine thermostat, it is probably stuck open.

It is located where the top radiator hose enters the engine block and is supposed to close when the engine is cold, thus prevent coolant from going to the radiator while the engine is heating up.

At engine operating temperature, it opens up, sends the coolant to the rad, and keeps the engine coolant at that constant temperature.

99% of the time, this is the culprit.

The other 1% could be a clogged/partially clogged heater core, or a busted heater core (accompanied by a coolant leak/loss over time) which fogs up the windows even more when the heater is on defrost.

Thermostat replacement is an easy, quick job and cheap.

Heater core replacement is a little bit more time/money consuming

Aug 27, 2008 | 2006 Ford Taurus

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