I posted this find on another Mustang... good info, so I thought I would post here as well...


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.

 

What impact would the above have on changing fan settings on an aftermarket tuner?

Currently the tuners based the temperatures on what would be perceived as the coolant temp. 190 for low speed and maybe 210 for highspeed.

I've always noticed that on my gt the fan is always on when i turn off the car. This occurs even after a long highway cruise where airflow would not be an issue.

 

I would rather have a CHT sensor anyway. The heat from combustion goes into the block and heat BEFORE it goes into the coolant, so getting one step closer to the heat source makes it that much more accurate and quicker responding.

Engines have been monitored by CHT for decades. The only reason they have to translate it to an equivalent water temperature is for the general public. If you put a CHT gauge in the dash with cold at 300, normal at 450 and hot at 600, people would freak out. Not to mention that they wouldn't have any idea what a CHT gauge WAS anyway.

As for the impact of fan settings, I would say "none". The whole point of the temperature conversion algorithm is to calculate what the cooling water is based on CHT alone. It might be off a few degrees, but then, most cheapy water temp sensors are off more than that anyway.

 

My 05 gt when doing "system check" on the info center lists an "ECT" as one of it's checks, seems silly if it doesn't have an engine coolent temp monitor to list it as "OK" on the info center.

 

It's probably the "inferred" ECT derived from the CHT.

 

Try here


http://www.modularfords.com/forums/s...d.php?t=111687

 

Guess this explains why when the blower whines and the water temp goes from 190 to 220 on the after market gauge the factory temp guage never moves.

 

I had wondered why I had an instantly warm engine temp gauge... now I know. Neato. Amazing what they can do with stuff, isn't it?

 

Actually, that is due to "other" programming. Basically, the factory programs the gauges to have three separate behaviors: 1) Warm up, 2) "Normal", 3) "Hot".

During "warm up", the gauge tracks the actual temperature fairly well. Not sure HOW well it tracks it, but the needle goes rises with a rising temperature as you would expect.

Once the temperature hits the lower bounds of the "normal" range, the needle goes to the center and stays there. It doesn't matter if the temps are on the low side of normal or on the high side of normal, the gauge stays in the center and the driver is fat and happy that their car is running "normally".

Once the temperature hits the upper bounds of the "normal" range, the needle goes over to the hot side and then starts tracking upward with the increasing temperature.

Basically, it is normally sensitive at the cold and hot extreme, but dead numb in the normal range. They do this so people won't be taking their car in when the temperature hits 220 and say it is "overheating" when Ford says overheating doesn't happen until (guess) 240. It also makes most people "feel good" to see there car running right in the middle of normal range all the time.

Just one of the fun things you can do when the computer controls the needles and not an actual sensor.

Side note: When GM came out with one of their first cars with a full digital dash (Not the Corvette, but I can't remember exactly what car it was), the engineers, being good engineers, spent a bit of time to make the fuel gauge as accurate as possible. When that sucker said you had half a tank, you had half a tank!

Very quickly, GM found they had a problem: a lot of people where taking their cars in to the dealers and claiming that the car got poor fuel economy. They investigated and found the reason people though their car was getting poor fuel economy:

The fuel gauge didn't stay on "Full" for the first 1/8 to 3/16 of a tank the way more "normal" cars did! It actually came down with the decreasing fuel level, so after you had driven 10 miles, you could actually see the needle wasn't solidly on the full mark.

GMs solution:

The reprogrammed the fuel gauge to stay on the the fuel mark for the first 1/4 of a tank!

 

How about some pics of where is the best spot to get a somewhat accurate reading of the water temp? SoundguyDave seems to be reading his temp just fine. Wonder if he can chime in...

 

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.

 

Chiming in... I have an analog sending unit installed in the tapped port located above and rearward of the last freeze plug on the driver's side. This location apparently shows lower coolant temps than drilling/tapping a sender in the crossover at the front of the motor, but is still sufficient for my needs, which is monitoring the differential of the temperature. My coolant temps run about parallel with my oil temps, with the coolant leading the oil by 5-10 degrees. Under "normal" driving conditions, I read between 170-185* for water temps (distilled water with one bottle of "WaterWetter" onboard, and approximately a 15% ethelyne glycol concentration). At the track, after about 10 minutes of running no lower than 3500RPM, and usually closer to 6500, the coolant temps in that location are around 230* without an oil cooler, and 210* with the cooler. At that point the temps are pretty much stabilized.

Hope this helps!

 

Photo? I'm sure it's very clear where it is for most, but I'm not as experienced!

 

It seems to me that it will also go lower if its colder. In the winter with my 160 Tstat that came with my whipple kit....it seems the temp is not in the center but a little lower. So it might read correct until a set norm temp where it stops in the middle.

 

Unfortunately, the stock gauges are all just fancy idiot lights.

Mike E

 

Nolagt,

If you have a 160T thermostat, in winter it is entirely possible that engine isn't ever reaching "normal" temps as far as the computer is concerned.

Mike,

They are a site better than an idiot light, but they don't keep you as well informed as a true gauge would either. At least with these gauges, when it DOES start getting hot, at least they will tell you about it BEFORE engine damage occurs.

 

Unfortunately, I don't have one handy, and it'll be more than a while before I get to spend any "quality time" with my car... Work is REALLY interfering with the race season this year! The port is pretty easy to find, though. If you look at the side of the engine block, starting where the trans bolts up, there is a plug in the block about 5" or so forward of the trans, and about 3" above the oil pan rail. The plug is just that, a simple pipe-thread plug with a hex socket in it (8MM, IIRC), and it's the only thing that a hex key would fit into in that area. Depending on what gauge sender you want to install, you'll most likely need an adapter. I got mine from Autometer, and I *think* it was M16x1.5 external threads, with a 1/8"NPT internal. I'm out of town (again), so I have none of my notes or receipts handy.

Pulling the plug is as simple as sticking in the hex key, and spinning out the plug. Be prepared for a good-sized coolant shower though! Next, install the sender into the adapter with teflon tape, then install the adapter into the block with teflon tape, and refill the coolant system. Run your wiring, and you're done!

 

What does the factory gauge read for those temperature ranges compared to your aux temperature gauge? Reason I ask, I was at BlackHawk Farms on Labor Day and experienced high temperature readings on the factroy gauge after running a few laps, running at about 6500 rpms for for some sections of the track. It cooled quickly to "normal" during a cool down lap. Runs in the "normal' range since I left the track in city, highway and construction traffic.

And what oil cooler would you recommend? OK scratch that last question, I found you posts in the Modular Mustangs Forum. Great info!

 

Just fwiw the Miata I used to own actually had "real" gauges. Not sure if the fuel gauge was 100 % right after reading above, but I know the temp and oil pressure gauges were pretty accurate. I could watch the oil pressure vary by rpm and also over time it would let me know it was due for an oil change. The pressure at idle was definitely lower after after about 2500-3000 miles. Kinda miss having that, but I'm not trading the Stang in for another one.

 

You must have had a 1990-94 Miata, because in 1995 Mazda made the oil pressure gauge an "idiot gauge" that only registered low, normal, and high, staying right in the middle of the normal range no matter what the oil pressure (unless outside the normal range). There is a kit to make the gauge show real oil pressure, but I'm glad my early Miata has the real OP gauge from the factory.