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.

hammeron

interesting stuff Q, thanks
for sharing

Mishri

THAT IS INSANE!! EVEN MY AQUARIUM CAME WITH A WATER TEMP. SENSOR!!!

alloutt

I would love someone to install a real sensor

Nuke

Sounds like you'll go into limp mode...

Simon1

You can buy a cap for your radiator that tells you the temp of the water if you want. Other than thati guess we're SOL.

moosestang

This website is really pissing me off lately! I made a post earlier, but apparently it didn't take.

There is a coolant temp sensor somewhere, unless the aeroforce interceptor gauge is just making it up. There are cylinder head temp sensors as well, but these do not display the same temp as the coolant sensor.

I couldn't tell you were the actual sensor is, but the pcm is getting a coolant temp from somewhere.

DoctorQ

Based on the Ford Service Manual (2005-2006), the S197 GT does not have an ECT sensor... only a CHT sensor (which runs hotter than coolant temp) which is mounted in the cylinder head, not in a coolant passage. Per an AeroForce engineer, the Interceptor reads the "ECT" off the PCM; however, the ECT value was derived ("inferred") from the CHT sensor, so you have to really trust whatever algorithm translated the CHT sensor reading to an ECT value before sending to OBDII port for display. Here is the response I received from AeroForce regarding is this issue:

I did some research on this and you are right, interesting. It displays what the PCM transmits when coolant temp is requested, which I understand to be a calculated temperature based on the CHT.

mrwglo

So it's guessing the temp! Nice.

Fullsayl

Well, it seems that in order to get the TRUE coolant temp, someone is going to have to start drilling. [:@]

That stinks!
~Matt