Thermostats explained
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| − | + | =How does a thermostat work ?= | |
| − | + | [[File:Thermostats shaw vs regular 001.jpg|thumb|left|300px|Shaw (left) vs. economy type thermostat]][[File:STATS 001.jpg|thumb|right|250px|A selection of thermostats]]<br style="clear:both"/> | |
| − | + | ===Question posed to Stant:=== | |
| − | + | (Stant is a well-known manufacturer of thermostats and related automotive parts.) | |
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<blockquote>Does an automobile thermostat in a 1975 Chevrolet with a 350 V8 engine traveling at highway speed regulate temp by opening fully then closing fully, repeating this cycle over and over, or does the thermostat regulate temp by partially closing as the coolant temp varies?</blockquote> | <blockquote>Does an automobile thermostat in a 1975 Chevrolet with a 350 V8 engine traveling at highway speed regulate temp by opening fully then closing fully, repeating this cycle over and over, or does the thermostat regulate temp by partially closing as the coolant temp varies?</blockquote> | ||
| − | + | ===The reply:=== | |
| − | + | <blockquote>The opening and closing of a thermostat is based on the temperature of the coolant running against the "heat motor". The heat motor is operated by a special wax that melts at a given temperature. As the wax melts, it expands and hydraulically pushes a pin that opens the valve allowing coolant to flow. I hope this helps. See the attached article for more details. | |
| − | <blockquote>The opening and closing of a thermostat is based on the temperature of the coolant running against the "heat motor". The heat motor is operated by a special wax that melts at a given temperature. As the wax melts, it expands and hydraulically pushes a pin that opens the valve allowing coolant to flow. I hope this helps. See the attached article for more details. | + | </blockquote> |
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| − | The attached article reads as follows: | + | ===The attached article reads as follows:=== |
'''Thermostats''' | '''Thermostats''' | ||
| − | The thermostat has two important jobs to perform; to accelerate engine warm-up and to regulate the engine's operating temperature. A quality thermostat ensures excellent fuel economy, reduces engine wear, diminishes emissions and blow-by, improves cold weather drivability, provides adequate heater output, and | + | The thermostat has two important jobs to perform; to accelerate engine warm-up and to regulate the engine's operating temperature. A quality thermostat ensures excellent fuel economy, reduces engine wear, diminishes emissions and blow-by, improves cold weather drivability, provides adequate heater output, and can help prevent overheating. This is accomplished by blocking the circulation of coolant between the engine and radiator until the engine has reached its predetermined temperature. The thermostat then opens as required in response to changes in coolant temperature to keep the engine's temperature within the desired operating range. |
Thermostats have a “rated” temperature such as 180F or 195F. This is the temperature the thermostat will start to open, give or take 3 degrees. | Thermostats have a “rated” temperature such as 180F or 195F. This is the temperature the thermostat will start to open, give or take 3 degrees. | ||
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Usually located within a metal or plastic housing where the upper radiator hose connects to the engine, most of today’s thermostats utilize the "reverse poppet" design, which opens against the flow of the coolant. Thermostats have a wax filled copper housing or cup called a "heat motor" that pushes the thermostat open against spring pressure. | Usually located within a metal or plastic housing where the upper radiator hose connects to the engine, most of today’s thermostats utilize the "reverse poppet" design, which opens against the flow of the coolant. Thermostats have a wax filled copper housing or cup called a "heat motor" that pushes the thermostat open against spring pressure. | ||
| − | As the engine's coolant warms up, the increase in heat causes the wax to melt and expand. The wax pushes against a piston inside a rubber boot. This forces the piston outward to open the thermostat. Within 3 or 4 degrees F. of the thermostat preset/rated temperature which is usually marked on the thermostat, the thermostat begins to unseat so coolant can start to circulate between the engine and radiator. It continues to open until engine cooling requirements are satisfied. It is fully open about 15-20 degrees above its rated temperature. | + | As the engine's coolant warms up, the increase in heat causes the wax to melt and expand. The wax pushes against a piston inside a rubber boot. This forces the piston outward to open the thermostat. Within 3 or 4 degrees F. of the thermostat preset/rated temperature which is usually marked on the thermostat, the thermostat begins to unseat so coolant can start to circulate between the engine and radiator. It continues to open until engine cooling requirements are satisfied. It is fully open about 15-20 degrees above its rated temperature. If the temperature of the circulating coolant begins to drop, the wax element contracts, allowing spring tension to close the thermostat, thus decreasing coolant flow through the radiator. |
On some applications, the thermostat performs an additional function. It closes off a bypass circuit inside the engine when it opens the radiator circuit. The bypass circuit circulates coolant inside the engine so that hot spots can’t form when the radiator circuit is closed. | On some applications, the thermostat performs an additional function. It closes off a bypass circuit inside the engine when it opens the radiator circuit. The bypass circuit circulates coolant inside the engine so that hot spots can’t form when the radiator circuit is closed. | ||
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'''Replacement Tips''' | '''Replacement Tips''' | ||
| − | + | *Don't overlook the water outlet covering the thermostat. Check for cracks, broken flanges, internal pitting and corrosion, and erosion at the hose neck (a real problem with most aluminum housings). The gasket surface must be flat and free from warping or deep scratches. | |
| − | + | *Scrape the mating surfaces on the thermostat housing and engine to remove all traces of old gasket material. Use care on aluminum because the soft metal can be easily scratched. | |
| − | + | *Temporarily stuffing a clean rag into the thermostat opening on the engine while the housing is removed helps keep debris out of the cooling system. | |
| − | + | *Install the new thermostat so the copper heat sensing element is toward the engine. If installed upside down, it won’t open. | |
| − | + | *Stant's Stat-Lok® thermostat gaskets are adhesive backed to make installation easier. | |
| − | + | *Torque the thermostat housing bolts evenly and to the manufacturer's recommendations. | |
| − | + | *To insure air has been removed from the cooling system after replacing a thermostat, be sure to run the engine a few minutes, let it cool, and refill the antifreeze as needed. | |
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| − | + | ==References== | |
| − | + | [http://www.stant.com/index.cfm?location_id=168 Stant thermostats] | |
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| − | + | [[Category:Cooling]] | |
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