Anyone Know How the Car Gets Coolant Temp??
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Bullitt Member
Joined: April 21, 2011
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From: Santa Clarita, CA
Anyone Know How the Car Gets Coolant Temp??
Any help, much appreciated. The Service Manual infers that only the 5.4L motor has an ECT (Engine Coolant Temp) sensor. What gives? Gauge (LS and Boss) simply connect to ECU via CAN BUS but manual doesn't say how ECU detects temp. A mystery for the moment!!
FR500 Member
Joined: July 1, 2008
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From: Oxford, UK
EDIT:
Here you go:
Cylinder Head Temperature (CHT) Sensor
Note: If the CHT sensor is removed from the cylinder head for any reason it must be replaced with a new sensor.
The CHT sensor is a thermistor device in which resistance changes with the temperature. The electrical resistance of a thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor (pull-up resistor) in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The CHT sensor is installed in the cylinder head and measures the metal temperature. The CHT sensor provides complete engine temperature information and is used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM initiates a fail-safe cooling strategy based on information from the CHT sensor. A cooling system concern, such as low coolant or coolant loss, could cause an overheating condition. As a result, damage to major engine components could occur. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability. For additional information, refer to Powertrain Control Software for Fail-Safe Cooling Strategy in this section.
Note: If the CHT sensor is removed from the cylinder head for any reason it must be replaced with a new sensor.
The CHT sensor is a thermistor device in which resistance changes with the temperature. The electrical resistance of a thermistor decreases as temperature increases, and the resistance increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so varying the resistance of the passive sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor (pull-up resistor) in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The CHT sensor is installed in the cylinder head and measures the metal temperature. The CHT sensor provides complete engine temperature information and is used to infer coolant temperature. If the CHT sensor conveys an overheating condition to the PCM, the PCM initiates a fail-safe cooling strategy based on information from the CHT sensor. A cooling system concern, such as low coolant or coolant loss, could cause an overheating condition. As a result, damage to major engine components could occur. Using both the CHT sensor and fail-safe cooling strategy, the PCM prevents damage by allowing air cooling of the engine and limp home capability. For additional information, refer to Powertrain Control Software for Fail-Safe Cooling Strategy in this section.
Last edited by PTRocks; Aug 18, 2011 at 08:29 PM.
Thread Starter
Bullitt Member
Joined: April 21, 2011
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From: Santa Clarita, CA
Perfect. Thanks.
Hmmm, I wonder how good it does this at higher temps. Strange that the LS has a very detailed engine temp gauge. I assume Ford is pretty confident in making this translation accurately.
and is used to infer coolant temperature
Bullitt Member
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From: Warsaw, IN
The stock thermostat is a 180° but these new systems read the head temperature directly which was typically around 8-10° hotter than the actual coolant temp in our tests. This means that a vehicle using our 170° thermostat will run somewhere between 178-200° according to the OEM sensor, depending upon conditions and fan settings.
Here's the thread.
http://www.svtperformance.com/forums...l#post10853899
Thread Starter
Bullitt Member
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From: Santa Clarita, CA
Thanks for the very informative feedback, guys! Much appreciated. We ran out of time last night and will end up shipping the car to MMP with the OEM (LS) temp gauge. Maybe best anyway if we are going to make comparisons to other LS's. Upon return, we will look for a way to replace the ECU-driven, cylinder-head-temp-derived, coolant temp gauge with something that measures true water temp. Go figure!!
FR500 Member
Joined: July 1, 2008
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From: Oxford, UK
Thanks for the very informative feedback, guys! Much appreciated. We ran out of time last night and will end up shipping the car to MMP with the OEM (LS) temp gauge. Maybe best anyway if we are going to make comparisons to other LS's. Upon return, we will look for a way to replace the ECU-driven, cylinder-head-temp-derived, coolant temp gauge with something that measures true water temp. Go figure!!
Thread Starter
Bullitt Member
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From: Santa Clarita, CA
Yeah, helpful maybe to others. We studied this from the manual as well as a detailed physical insopection from the top side of the engine. I don't think any threaded ports available. On the 5.4 Ford GT Block, there are two allen plugs underneath into water passages and I need to see if there is anything similar on the Coyote engine. Otherwise, it may be the old-school (yuck!) way of a probe in the top radiator hose at point 20 in the illustration.
Shelby GT350 Member
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From: Sioux Falls, SD
Thread Starter
Bullitt Member
Joined: April 21, 2011
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From: Santa Clarita, CA
I'm one of the others for which this was helpful. Wish I had Kendall's skills with a wrench. 
Thanks for posting it.
Thanks for posting it.
PTRocks - you are a star, my friend! Thanks for the great suggestion!
Member
Joined: December 10, 2010
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From: Motor City, USA
ECT is inferred from CHT. Your desire to measure "true" water temp may or may not match what the PCM is referencing when controlling the motor. Not sure what the added value will be by tapping into one point in the cooling system vs the another (vs the inferred ECT values)... Interesting info, for sure, but not sure what you'd get from it vs the CHT-derived value (it's pretty well correlated to ECT). Just my 2 cents... Good luck!
Thread Starter
Bullitt Member
Joined: April 21, 2011
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From: Santa Clarita, CA
ECT is inferred from CHT. Your desire to measure "true" water temp may or may not match what the PCM is referencing when controlling the motor. Not sure what the added value will be by tapping into one point in the cooling system vs the another (vs the inferred ECT values)... Interesting info, for sure, but not sure what you'd get from it vs the CHT-derived value (it's pretty well correlated to ECT). Just my 2 cents... Good luck!
GT Member
Joined: August 19, 2011
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From: New York
Does anyone know the thread size at the block plug for the block heater. Seems like a good place for a coolant temp sender. As far as installing a tee for oil temp wouldn't the dead end give a false temp reading as the oil won't be "changing" across the sender, but will be stagnant there. Typically oil temp sensors are put in the middle of the sump or oil tank as that oil in constantly being circulated. I am interested in whether the temp fluctuates when taken off of the tee or if it is slow to rise and slow to decrease when under varying rpm load on track. Supposedly the Boss motor builds and sheds oil temp rapidly when running above and below 6500 rpm.
Steve
Steve
Shelby GT350 Member
Joined: November 20, 2010
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From: Sioux Falls, SD
S197's point is important in that the PCM is responding to CHT so that becomes the value that most matters to me. Even if we get true ECT, the PCM would still be controlled by CHT sending the engine into limp mode at 250F. Not that there may not be ogre benefits to lower ECT on track, but I'm told it's designed to run 220-240. The next question: Does the PCM retard some timing when CHT reaches a certain value below 250F?
Thread Starter
Bullitt Member
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From: Santa Clarita, CA
Does anyone know the thread size at the block plug for the block heater.
I am interested in whether the temp fluctuates when taken off of the tee or if it is slow to rise and slow to decrease when under varying rpm load on track.
Shelby GT350 Member
Joined: November 20, 2010
Posts: 2,382
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From: Sioux Falls, SD
Kendall I've noticed the exact same phenomenon on the track relative to ECT and the response was more immediate than oil temp. Not sure what the track layout is at MMP but sounds like you're running the full course. If so, you should be able to see that pretty well in the long straightaway. I found ECT dropping from 246 to 235 on the 4-5 shift between 9 & 10 at BIR. It happened within a few seconds.
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