Water Temp Guage Accuracy Part2 (probe placment) Long
04-13-2004, 01:25 AM
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Car: 1982 CAMARO;
Engine: 1985 LB9;
Transmission: T-5/
Water Temp Guage Accuracy Part2 (probe placment) Long
PROBE PLACEMENT for the WATER TEMP GAUGE
Another topic worthy of mention is where to install the temperature probe at the engine. The most sensible place to install the probe for a water temperature gauge is at the intake manifold water jacket, near the thermostat housing.
The water thermostat is used to control circulation of the coolant, which will ultimately regulate the coolant temperature in the engine. The purpose of the Water Temp gauge is to monitor coolant temperature. Therefore; with a 180 degree water thermostat in the engine, and the probe installed next to the thermostat, the Water Temp gauge should read about 180 degrees under normal operating conditions.
With the probe at this location (next to the water thermostat) we actually monitor cooling system performance, which is the purpose of the gauge. If the cooling system is adequate, then the water temperature measured at this point should be about the same as the temperature rating of the thermostat. We install the water thermostat to maintain engine coolant at the temperature we desire for the particular application. But if the gauge reading climbs significantly above the rating of the water thermostat, then the cooling system is not adequate to keep the coolant at the desired temperature.
Move the sending unit from the head to the intake manifold. The new location places it near the water thermostat. The switch mounted in the head always interfered with changing a spark plug, and installation near the water thermostat will do a better job of monitoring the cooling system performance.
With the sending unit removed from the head, You Will also notice that the threaded pipe adapter was shrouding the sensor part of the sending unit rather than placing the sensor directly in the path of coolant flow. (See the unit in the above photo). With the installation of the sending unit in the intake manifold, first installe the threaded pipe adapter and then cut off the hex-head! Removal of the hex-head allowed the sensor to protrude entirely through the threaded pipe adapter, which places the sensor directly in the path of coolant flow.
PROBE PLACEMENT with a Water Temp WARNING LIGHT
The most sensible place to install a switch for a water temp warning light might be at the cylinder head, which is what the factory often did. (Many of us are familiar with the factory installed temperature switches for the warning lights, at the cylinder head.) However, these water temperature switches for the warning lights were calibrated to light-up the warning light at very hot temperatures, often at temperatures between 235F and 260degrees F.
In many engines, the water in the cylinder head is hotter than at any other location, and when the engine is under load, the combustion chamber pressure and temperature will be increased. Also at high RPM, the combustion cycles will occur at a more frequent rate than at low RPM. (Combustion chamber temperature may be about 1,450degrees F.)
Metal at the cylinder head will conduct the heat from the internal surfaces at the combustion chamber of the head. And the coolant, which is in contact with the water jacket surfaces in the cylinder head, will then absorb the heat and conduct the heat away from the head. At the radiator, the heat will be dissipated to the air flowing through the radiator. It’s just normal cooling system function—it’s what the coolant is intended to do for us. But…expect that cylinder heads will have “hot spots;” which is to say that there will be places in the head where the coolant temperature will be significantly higher than the water thermostat rating.
When we pull an engine hard, coolant in the cylinder head will be the first to rise above “normal” temperature. Also because the heads will have “hot spots,” the cylinder head is often the most likely to break, or we may have head-gasket failure, as a result of severe overheating.
Therefore the head is a practical place to install a switch for the Water Temp warning light, provided that the switch is calibrated to recognize dangerous cylinder head temperatures. And if we have an over-heating problem, then hopefully the “Water Temp Warning Light” will light up to warn us that we may do some damage if we continue running the engine.
By the time it reaches the water thermostat, this hotter coolant from areas at the cylinder head will be mixed with coolant from other areas of the engine; the thermostat does not directly read these hot spots. The coolant leaves the engine through the water thermostat, and so the thermostat regulates the average temperature of the coolant in the engine. (It’s another reason why a Water Temp gauge probe should be placed near the water thermostat.)
Where gauges are concerned, be aware that even a brief burst of acceleration at high RPM can greatly increase cylinder head temperature—which is a good reason not to install the probe for a Temp gauge in the cylinder head. (Because the gauge could indicate that we have an over-heating problem every time we pull the engine hard or run up the RPM.)
Considering the complication involved with mass-producing cars, the “factory guys” do some very good work. But we can expect that the factory did not always build everything perfect.
There may have been some factory installed Water Temp gauges with the coolant temperature switch in the cylinder head. (Not to say that this is proper installation.) We can only speculate about why the factory would do these installations. It might have been that the intake manifold did not have a drilled and threaded hole for the water temp switch, with some engine options. Or, the temp gauge switch could have been left in the head to keep wire harness routing the same with “warning light” and “gauge equipped” cars.
No matter what the factory did, as Hot Rodders our job is to improve the cars. We should borrow the best of factory ideas, and adapt the best technology to our Hot Rods. We even borrow ideas and equipment from different makes or models, as well as from different production years. We must sort everything, and discard the not-so-good ideas. We should test a few of our own ideas too.
It makes sense that with many years of ordinary Chevy V-8 engines with cast iron heads, the probe for the Water Temp warning light was installed in the driver’s side cylinder head (not the passenger side). And… we should also consider that the factory guys at Chevy used “reverse water flow” at the cooling system when the cylinder compression ratio was increased with the high-performance small block, the LT1 Corvette from the early 1990’s. No doubt the reverse direction water flow was intended to reduce detonation by routing the cool water through the heads first—rather than somewhat pre-heating the water as with the traditional flow direction through the block and then up through the heads.
The point to the above discussion is that obviously water temperature is not the same at all locations throughout the engine. And it’s for this reason that we should install the probe for the Water Temp gauge near the water thermostat in the engine. With the probe installed next to the water thermostat, the Water Temp gauge will indicate the temperature of the hot coolant being discharged from the engine. With this installation we can monitor cooling system performance; we will know if the cooling system is able to keep the temperature down to the rating of the water thermostat.
ENGINE “COOLANT” (anti-freeze/anti-boil) AND A PRESSURE CAP AT THE RADIATOR WILL INCREASE BOILING TEMPERATURE OF THE COOLANT
Another topic worthy of mention is where to install the temperature probe at the engine. The most sensible place to install the probe for a water temperature gauge is at the intake manifold water jacket, near the thermostat housing.
The water thermostat is used to control circulation of the coolant, which will ultimately regulate the coolant temperature in the engine. The purpose of the Water Temp gauge is to monitor coolant temperature. Therefore; with a 180 degree water thermostat in the engine, and the probe installed next to the thermostat, the Water Temp gauge should read about 180 degrees under normal operating conditions.
With the probe at this location (next to the water thermostat) we actually monitor cooling system performance, which is the purpose of the gauge. If the cooling system is adequate, then the water temperature measured at this point should be about the same as the temperature rating of the thermostat. We install the water thermostat to maintain engine coolant at the temperature we desire for the particular application. But if the gauge reading climbs significantly above the rating of the water thermostat, then the cooling system is not adequate to keep the coolant at the desired temperature.
Move the sending unit from the head to the intake manifold. The new location places it near the water thermostat. The switch mounted in the head always interfered with changing a spark plug, and installation near the water thermostat will do a better job of monitoring the cooling system performance.
With the sending unit removed from the head, You Will also notice that the threaded pipe adapter was shrouding the sensor part of the sending unit rather than placing the sensor directly in the path of coolant flow. (See the unit in the above photo). With the installation of the sending unit in the intake manifold, first installe the threaded pipe adapter and then cut off the hex-head! Removal of the hex-head allowed the sensor to protrude entirely through the threaded pipe adapter, which places the sensor directly in the path of coolant flow.
PROBE PLACEMENT with a Water Temp WARNING LIGHT
The most sensible place to install a switch for a water temp warning light might be at the cylinder head, which is what the factory often did. (Many of us are familiar with the factory installed temperature switches for the warning lights, at the cylinder head.) However, these water temperature switches for the warning lights were calibrated to light-up the warning light at very hot temperatures, often at temperatures between 235F and 260degrees F.
In many engines, the water in the cylinder head is hotter than at any other location, and when the engine is under load, the combustion chamber pressure and temperature will be increased. Also at high RPM, the combustion cycles will occur at a more frequent rate than at low RPM. (Combustion chamber temperature may be about 1,450degrees F.)
Metal at the cylinder head will conduct the heat from the internal surfaces at the combustion chamber of the head. And the coolant, which is in contact with the water jacket surfaces in the cylinder head, will then absorb the heat and conduct the heat away from the head. At the radiator, the heat will be dissipated to the air flowing through the radiator. It’s just normal cooling system function—it’s what the coolant is intended to do for us. But…expect that cylinder heads will have “hot spots;” which is to say that there will be places in the head where the coolant temperature will be significantly higher than the water thermostat rating.
When we pull an engine hard, coolant in the cylinder head will be the first to rise above “normal” temperature. Also because the heads will have “hot spots,” the cylinder head is often the most likely to break, or we may have head-gasket failure, as a result of severe overheating.
Therefore the head is a practical place to install a switch for the Water Temp warning light, provided that the switch is calibrated to recognize dangerous cylinder head temperatures. And if we have an over-heating problem, then hopefully the “Water Temp Warning Light” will light up to warn us that we may do some damage if we continue running the engine.
By the time it reaches the water thermostat, this hotter coolant from areas at the cylinder head will be mixed with coolant from other areas of the engine; the thermostat does not directly read these hot spots. The coolant leaves the engine through the water thermostat, and so the thermostat regulates the average temperature of the coolant in the engine. (It’s another reason why a Water Temp gauge probe should be placed near the water thermostat.)
Where gauges are concerned, be aware that even a brief burst of acceleration at high RPM can greatly increase cylinder head temperature—which is a good reason not to install the probe for a Temp gauge in the cylinder head. (Because the gauge could indicate that we have an over-heating problem every time we pull the engine hard or run up the RPM.)
Considering the complication involved with mass-producing cars, the “factory guys” do some very good work. But we can expect that the factory did not always build everything perfect.
There may have been some factory installed Water Temp gauges with the coolant temperature switch in the cylinder head. (Not to say that this is proper installation.) We can only speculate about why the factory would do these installations. It might have been that the intake manifold did not have a drilled and threaded hole for the water temp switch, with some engine options. Or, the temp gauge switch could have been left in the head to keep wire harness routing the same with “warning light” and “gauge equipped” cars.
No matter what the factory did, as Hot Rodders our job is to improve the cars. We should borrow the best of factory ideas, and adapt the best technology to our Hot Rods. We even borrow ideas and equipment from different makes or models, as well as from different production years. We must sort everything, and discard the not-so-good ideas. We should test a few of our own ideas too.
It makes sense that with many years of ordinary Chevy V-8 engines with cast iron heads, the probe for the Water Temp warning light was installed in the driver’s side cylinder head (not the passenger side). And… we should also consider that the factory guys at Chevy used “reverse water flow” at the cooling system when the cylinder compression ratio was increased with the high-performance small block, the LT1 Corvette from the early 1990’s. No doubt the reverse direction water flow was intended to reduce detonation by routing the cool water through the heads first—rather than somewhat pre-heating the water as with the traditional flow direction through the block and then up through the heads.
The point to the above discussion is that obviously water temperature is not the same at all locations throughout the engine. And it’s for this reason that we should install the probe for the Water Temp gauge near the water thermostat in the engine. With the probe installed next to the water thermostat, the Water Temp gauge will indicate the temperature of the hot coolant being discharged from the engine. With this installation we can monitor cooling system performance; we will know if the cooling system is able to keep the temperature down to the rating of the water thermostat.
ENGINE “COOLANT” (anti-freeze/anti-boil) AND A PRESSURE CAP AT THE RADIATOR WILL INCREASE BOILING TEMPERATURE OF THE COOLANT
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