There is no water temp sensor in a GT !

[DoctorQ]

Last week I posted an inquiry as to the accuracy of the OEM H20 temp sensor and its specific location (as I have seen various theories as to its whereabouts). Well, after a bit of investigating (and the help of the Factory Service Manual DVD) it appears the 2005-2006 (and most likely 2007+) Mustang GT does NOT have a H20 temp sensor. Rather, the GTs are configured with a CHT (Cylinder Head Temp) sensor. I’m passing this along for additional verification and/or for those who may be wondering the same thing I was.

The 2005+ 4.0L V6 has an ECT (Engine Coolant Temp) sensor which is mounted in an actual coolant passage. The issue with ECT sensor equipped vehicles is that an accurate reading of CHT cannot be obtained (important for fuel economy and emissions). The 2005+ 4.6L GT is equipped with a CHT sensor, no ECT. The CHT is mounted into the wall of the cylinder head and is NOT connected to any coolant passages. After reading the CHT Patent (method to infer engine coolant temperature in cylinder head temperature sensor equipped vehicles, Patent issued: Feb 2000), the CHT can be up to 70* F hotter than the ECT (and would send false ECT overheating signals to gauge). This patent addressed the algorithms now used in the PCM to interpret the CHT temp and infer the ECT (which in turn is communicated back to the gauge and the OBDII port for scan gauges).

http://www.freepatentsonline.com/RE40262.html


I also found this on another Ford forum regarding CHT sensors. In this case, the vehicle’s ‘temp’ gauge was pegged on H and was asking what might be the issue (as he had no physical signs of over-heating). Here was the response:

I don't think the engine is running hot because of this feature. According to this if the gauge is all the way on hot which it is most of the time then the injectors should be disabled by the computer.

The Cylinder Head Temperature(CHT) sensor:

- Is mounted into the wall of the cylinder head and is not connected to any coolant passages.- Sends a signal to the PCM indicating the cylinder head temperature.

- If the temperature exceeds: 126°C (258°F) the PCM disables four fuel injectors at a time. The PCM will alternate which four injectors are disabled every 32 engine cycles. The four cylinders that are not being fuel injected act as air pumps to aid in cooling the engine.

- If the temperature exceeds: 154°C (310°F), the PCM disables all of the fuel injectors until the engine temperature drops below: 154°C (310°F).

-If the engine reaches critical temperature, the following happens:- The coolant temperature gauge pointer will read fully hot at 121°C (250°F). - The check gauge warning indicator will illuminate.- DTCs are set.





Anyway, I found this to be interesting and informative. I did not validate with my GT (i.e., tear off the intake looking for CHT sensor) nor do I own a 4.0L, so couldn’t confirm the ECT location. Just posting some Internet findings and what I found in the Factory Service Manual. If anyone has better information, please post.

 

[TexasBlownV8]

Learn something every day, huh. I sure didn't know that, but i do now. And even in my factory manual, it shows the CHT sensor on the GTs and no coolant temp sensor.
So, does this change your original need to find and use the coolant sensor, or whatever you were going to do? Or does this mean you will be putting in a temp sensor somewhere? You should be able to get the CHT PID value, if that's of any help.

[Kudos to the good info. Great research!]

 

[94tbird]

i have the factory CHT sensor and my Autometer water temp sensor. they are usually dead on with each other, but when they are not it is only 1-3 degrees off from each other

 

[Hawgman]

i have the factory CHT sensor and my Autometer water temp sensor. they are usually dead on with each other, but when they are not it is only 1-3 degrees off from each other

So are you getting a tempature reading from the CHT via datalogging or have you somehow identified a gauge that the factory CHT will connect to and read a proper tempature?

 

[marcspaz]

You can install a universal ECT sensor anywhere in the coolant line (usually the upper rad hose) and connect it directly to a ECT gauge to get a reading. The kits are about $35 and the sky is the limit on the gauge...

There are some that est flow rate too.

 

[twinscrewed]

I knew of this before I did my Whipple, so I installed my temp sensor in place of the bleed off valve in the Whipple supplied crossover. Seems to be very accurate, but wow these cars run warmer than I was used to.

 

[andyman]

I put my water temp sensor in the block, on the drivers side. Works great there!

 

[W1ldcat]

Is there any concern in using what the OBD port is calling H2O temp? Am I not seeing how hot my coolant actually is?
Thanks...

 

[dustindu4]

I've known about this for 3 years, since I put a water temp gauge in. My autometer sensor is on the passenger side of the coolant crossover tube

 

[DoctorQ]

Learn something every day, huh. I sure didn't know that, but i do now. And even in my factory manual, it shows the CHT sensor on the GTs and no coolant temp sensor.
So, does this change your original need to find and use the coolant sensor, or whatever you were going to do? Or does this mean you will be putting in a temp sensor somewhere? You should be able to get the CHT PID value, if that's of any help.

[Kudos to the good info. Great research!]

If I knew for a fact that the temperature being read off the OBDII (via a scan gauge) was the "inferred" ECT, I'm good. However, if the OBDII is picking up the CHT sensor temp (prior to ECT recalculation), then I'd have to install a separate ECT sensor directly to separate H2O temp gauge. I was trying to avoid drilling/tapping a new sensor. Based on one of the posts above, sounds like there are ECT kits that run "in-line" between radiator hose and thermostat housing?

 

[marcspaz]

Depends on the kit. Some are in-line, some are just sensors you can use to tap the block or radiator. The in-line units are more expensive, but they tend to give flow rates too. Stand-alone sensor on the block or radiator only give temps, but the kits are far less expensive.

Shop around, I'm sure you will find something you like.

 

[94tbird]

So are you getting a tempature reading from the CHT via datalogging or have you somehow identified a gauge that the factory CHT will connect to and read a proper tempature?

I have datalogged it with SCT and i have used the aeroforce performance gauges to read the CHT

 

[don_w]

I was trying to avoid drilling/tapping a new sensor.

I just used the existing port on the coolant crossover tube. Works fine for me.

 

[DoctorQ]

I just used the existing port on the coolant crossover tube. Works fine for me.

Don.. are you referring to item #11 in the attached? If so, there's already a threaded port on this crossover assy?

 

[don_w]

Don.. are you referring to item #11 in the attached? If so, there's already a threaded port on this crossover assy?

Yes, in the area where it shows bolt #1 going.

 

[DoctorQ]

Confirmed from FORD Engineering: No ECT Sensor in GT

I asked Ford Engineering to confirm my Post #1... and they have. The 05-08 Mustang GT does NOT have an ECT sensor... Here's Ford's response to the question "Does the 2006 Mustang GT have an ECT sensor":

Your mustang does not have an ECT sensor. Ford Engineering advises that the CHT sensor is more accurate as it measures metal temperature. Sensors that are mounted in coolant will not measure temperature if there is a loss of coolant. On applications (GT) that do not have an ECT sensor, the CHT sensor is used to determine the engine coolant temperature. To cover the entire temperature range of both the CHT and ECT sensors, the PCM has a dual switching resistor circuit on the CHT input, switching from the cold end to hot end with increasing temperature and back with decreasing temperature. There is a temperature to voltage overlap zone within this zone and it is possible to have either a cold end or hot end voltage at the same temperature. For example (194 f) the voltage could read either 0.60 volts or 3.71 volts. Based on the chart that we use, here are some more voltage examples: 212 degrees = 0.46 volts (cold end) 3.41 volts ( hot end) =2.034 k ohms 194 degrees=0.60 volts (cold end) 3.71 volts (hot end) =2.75 k ohms, and so on. Hope this helps.

 

[ClassJ]

How did you get them to give you that response...?

The closest response I have ever gotten from ford factory on anything technical was "bring it to the dealer"