How does the PCM Read head and Coolant temp?

[2k05gt]

Quick recap, I replace the Heads in my 2005 with 80K with 2007 heads prompted by a bent valve. I had a overheating issue after the head swap so I changed the gasket a second time.

The car still runs Hot no over heating though.
From Cold start at idle it takes 5-7 min to bring it up to running temp, it will stat at 210 Deg at idle for 20 minutes (head temp 220)

after a short cruise the temps will be around 215 (head temps 228)
At Idle for 20 Min temps will be around 219 (head temps 230)
If I turn in the A/C it will go up to 221 and Heat will drop it to 217.

Long Cruise in stop and go traffic it will run 225-230 if I sit at idle for 20 min it wil stay at 230 (head temps 240)

I stopped by Excessive Motorsports in Manassas, VA and Had Chris check it out, he use a Laser Heat gun to check the temps, My Aeroforce Intercepter and his hand held diag tool read the temps coolent temos at 230 (head temps 240) but shot the head at 195, shot the back side of the heads near the head temp sensor at 208, the hoses were not over 160 and the coolant was 165 in the bottle.

Is it possable that the Coolant sensor and Head temp sensosr are off, the degree of different between the Head temp and Coolant temp was 10-12 deg difference at any given time.

I will have Ford look at it on saturday, I have no Idea why it runs so hot.
I put in a new Radiator, I converted the crossover to a 2007 style (to match the heads, NewT Stat and Water pump. The Relay for th efan is real hot but that could be due to it running all the time.

Thanks for the help.

 

[saleen07gt]

I don't believe the 2 temps are going to match. Where is the needle at on the factory gauge at normal opperating temp. ?

 

[dysan]

I thought that the pcm inferred the coolant temp from the cylinder head temp sensor in the engine valley. I don't think there is a specific coolant temp sensor and that's why some people are using these for their exact coolant temps.....

http://www.glowshiftdirect.com/Water-Hose-Adapters.aspx

 

[bcb06gt]

I thought that the pcm inferred the coolant temp from the cylinder head temp sensor in the engine valley. I don't think there is a specific coolant temp sensor and that's why some people are using these for their exact coolant temps.....

http://www.glowshiftdirect.com/Water-Hose-Adapters.aspx

+1 on no actual coolant temp sensor. I too think it is inferred.

 

[scramblr]

With my Aeroforce reading head temp and my AM Cobalt gauge reading coolant temp, 10-12* difference between the two is not abnormal.

 

[tmcolegr]

With my Aeroforce reading head temp and my AM Cobalt gauge reading coolant temp, 10-12* difference between the two is not abnormal.

Same here. My AM Cobalt electric full sweep coolant temp gauge (sender is in the rear of the block on the driver's side) reads about 10º-12º warmer than my Areoforce which takes information directly from the PCM via the CHT sensor.

 

[scramblr]

Same here. My AM Cobalt electric full sweep coolant temp gauge (sender is in the rear of the block on the driver's side) reads about 10º-12º warmer than my Areoforce which takes information directly from the PCM via the CHT sensor.

Interesting, mine is the exact opposite. I have the exact same AM Cobalt as you, but my sender is on the cross-over (pass side) and reads 10-12* cooler than the CHT sensor.

 

[tmcolegr]

Not trying to high jack this thread, but when my Cobalt gauge is reading 210º, my Aeroforce gauge reads 200º and the low speed cooling fan comes on. Jim Sr. has the fans set to come on in the tune at 200º.

 

[2k05gt]

So the Coolant Temp is a Computer Calculation from the CHT sensor?

I turned on the A/C today and the Temps Shot up 242 Coolant 250 Head Temp. Ford Tech seams to think I have a Crack in the Head or a warped Head, No other reason for the temps to run this hot while at idle after driving.

 

[iwaxmyjimmy]

So the Coolant Temp is a Computer Calculation from the CHT sensor?

I turned on the A/C today and the Temps Shot up 242 Coolant 250 Head Temp. Ford Tech seams to think I have a Crack in the Head or a warped Head, No other reason for the temps to run this hot while at idle after driving.

No the ECT sensor is on the oil filter housing. right behind the power steering pump, and the CHT sensor is on the passenger side cylinder head around the #3 cylinder water jacket. Its very possible for the cylinder head to have a crack in it, but I'm not completely sold on the idea of it. I'd pull both sensor just to make sure there isn't and corrosion or if they are cracked (they are just brass/copper and plastic)

 

[tmcolegr]

No the ECT sensor is on the oil filter housing. right behind the power steering pump

I sure hope you're not referring to a 4.6L 3V. The sensor you just referenced is the oil pressure sensor and has nothing to do with engine temps.

This issue has been covered several times before. Our engines do NOT have a ECT sensor. They only have a CHT sensor. The PCM gathers information from the CHT sensor.

05 & 06 MY vehicles had a oil temp sensor in the passenger side of the oil pan but this sensor but was deleted on 07+ MY vehicles.

 

[2k05gt]

I sure hope you're not referring to a 4.6L 3V. The sensor you just referenced is the oil pressure sensor and has nothing to do with engine temps.

This issue has been covered several times before. Our engines do NOT have a ECT sensor. They only have a CHT sensor. The PCM gathers information from the CHT sensor.

05 & 06 MY vehicles had a oil temp sensor in the passenger side of the oil pan but this sensor but was deleted on 07+ MY vehicles.

So I am confused, the Head temp and coolant temps all come from one sensor on the head? the PCM just take the head temp and does some equesion to come up with the coolant temp, so if the head temp sensor is reading wrong everything is off?

 

[tmcolegr]

So I am confused, the Head temp and coolant temps all come from one sensor on the head? the PCM just take the head temp and does some equesion to come up with the coolant temp, so if the head temp sensor is reading wrong everything is off?

Correct!! There is no coolant temp sensor on our 4.6Ls - only the CHT sensor

Now wasn't that an epiphany

 

[tmcolegr]

Check out the section on the CHT sensor

 

[iwaxmyjimmy]

Check out the section on the CHT sensor

F5AZ12A648AB- ECT sensor
4L3Z12A648AB- ECT sensor
3L7Z6G004BA- CHT sensor

These are for a 08 mustang GT

Edit: Those are for the 5.4L, it is actually inferred. I had to go back and read up on those, my bad

 

[RRRoamer]

Think of it this way: Why do we CARE what the water temperature is?
1) It gives us an INDICATION of the actual engine temperature
2) It lets us know if we are getting close to boiling over the engine.

In truth, we are FAR more interested in the ENGINE temperature. The water temperature is only an indirect measurement of what really matters. The cylinder head temperature on the other hand IS what we are interested in. It directly measures the engine temperature.

The problem is, 99.99% of all car drivers would have no CLUE how to read a CHT gauge or what is or is not a problem. But they ARE used to looking at water temperature gauges, so Ford gave us one. Just an "inferred" temp, but close enough. The PCM DOES understand how to read and interpret the CHT, so that is what IT goes by.

This is kind of like why almost all car temp gauges do NOT have numbers on them. Instead, you have a "L [Normal] H" deal. To make it even worse, most times on modern cars the PCM LIES about the temperature anyway! Why do you think your temp gauge goes right to the middle of "Normal" (which is where we all want to see it!) and stays there unless something gets out of wack? It's so people won't be taking cars in to be "repaired" just because they are running on the high side for one reason or another. If it doesn't hurt the car, the computer considers it normal.

They do the same thing on fuel gauges. Back in the early '80s, GM came out with one of the first cars to have an all digital dash. They programmed the fuel gauge to be VERY accurate: When it said it was full, it was full. When it was empty, it was truly empty. And a 1/2 tank meant you had half your fuel remaining.

They got so many warranty service requests over this it was stupid! People complained the car didn't get very good fuel economy.

Why?

Because the needle didn't stay on full very long!

People complained that the fuel tank was defective.

Why?

Because when the needle was fully on the "E" mark, the car ran out of gas!

Eventually, the "solved" all the cars problems with a service update that simply reprogrammed the fuel gauge.

You guessed it! They made it lie!

 

[Simon]

So I am confused, the Head temp and coolant temps all come from one sensor on the head? the PCM just take the head temp and does some equesion to come up with the coolant temp, so if the head temp sensor is reading wrong everything is off?

If for whatever reason you decide to repalce your CHT sesnor. I have an extra if you would like it. It won't fit in my car (hits the bottom of the KB manifold) and it's brand new.

You can have it.

 

[redstangs9308gt]

dude I was having simular troubles out of my 94 mustang gt. It was telling me I was boiling and I wasn't so replaced all coolant related sensors then I noticed my ac pump wasn't turning off. Only time it would stop running is when I turned the ac off on the dash. I replaced high and low side ac sensors and guess what...No more wacky reading of temp and ac was kicking in and out like it should be. I also remember if you was low on refridgrant the car wouldn't idle right either. soo if you can find out if these new cars are like that maybe that is your problem I hope anyways.

 

[2k05gt]

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 (He had no physical signs of over-heating). Here was the response:

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.

The 2005-2008 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.

 

[redstangs9308gt]

sent you a pm...