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Old 04-21-2013, 02:28 AM   #1
erhodes
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Coolant temp sensor!

Hey guys I desperately need some help. I need to know where exactly the coolant temp sensor on a 2005 ford focus ZX5 with the 2.0L duratec is. I was sold a coolant temp sensor today in an effort to solve an issue ive been experiencing. Ford parts calls the sensor in the middle of the head in between the 2 and 3 coils a manifold temp sensor-not a cylinder head temp sensor. but they do not call out a coolant temp sensor. I cannot find any info on this anywhere on the web. Everyone says "they don't have an ECT, they have cylinder head temp sensors." someone please shed some light on this for me


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Old 04-21-2013, 03:59 AM   #2
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Coolant as in anti-freeze? Coolant temp sensor as in a thermostat? http://www.wholesalefordparts.com/sh...roduct=8759449 Maybe this will help? Idk. I have a ZETEC so not really sure... should be pretty much the same I would think...Mine is right under the coil pack inside it's housing bolted onto the engine block...
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Old 04-21-2013, 04:09 AM   #3
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Could possibly be between spark plugs 2 and 3... or under the cam/valve cover? Just have to look around man...

Last edited by Kodyston; 04-22-2013 at 05:57 AM.
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Old 04-21-2013, 09:22 AM   #4
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What is the issue you are trying to solve? The Zetec uses a cylinder head temp sensor it is the dry type and measures the metal temp directly. They don't go bad very often.
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Old 04-21-2013, 09:31 AM   #5
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That's right, it's in the valve cover. You'll need a long extension.

This has to do with thermodynamics. That is your engine temp sensor, and it doesn't matter whether it's in the cylinder head or the thermostat housing- it's measuring the coolant temp. I totally forget what that law is called, but it's what keeps wax filled paper cups burning without melting when floating on water. Heat conducts and dissipates quickly to an equilibrium with all things in contact with the source. Your combustion chambers and exhaust gasses can reach temps over 1500F which is more than enough to melt aluminum. Yet it doesn't because around that aluminum is coolant under pressure flowing through the cylinder head. That acts as a heat sink and pulls excess heat from the combustion chambers out to the radiator where it is cooled off.

Yes, I'm not totally right, it does matter where the temp sensor is located in the cooling system. In the center of the cylinder head is the most efficient place because that's closest to where the majority of heat is being created. In this case, it's a matter of reaction time. Yes, the heat will dissipate and the system will reach equilibrium eventually, but it will change faster closest to the heat.

People who use different terminology are not wrong either. The temp sensor is in the cylinder head- right? It is measuring the cylinder head temp- right? They are only wrong if they think that the cylinder head is hotter than the coolant for more than a split second. The exhaust is, but that's not fluid cooled is it?
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Old 04-22-2013, 05:56 AM   #6
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Originally Posted by whynotthinkwhynot View Post
That's right, it's in the valve cover. You'll need a long extension.

This has to do with thermodynamics. That is your engine temp sensor, and it doesn't matter whether it's in the cylinder head or the thermostat housing- it's measuring the coolant temp. I totally forget what that law is called, but it's what keeps wax filled paper cups burning without melting when floating on water. Heat conducts and dissipates quickly to an equilibrium with all things in contact with the source. Your combustion chambers and exhaust gasses can reach temps over 1500F which is more than enough to melt aluminum. Yet it doesn't because around that aluminum is coolant under pressure flowing through the cylinder head. That acts as a heat sink and pulls excess heat from the combustion chambers out to the radiator where it is cooled off.

Yes, I'm not totally right, it does matter where the temp sensor is located in the cooling system. In the center of the cylinder head is the most efficient place because that's closest to where the majority of heat is being created. In this case, it's a matter of reaction time. Yes, the heat will dissipate and the system will reach equilibrium eventually, but it will change faster closest to the heat.

People who use different terminology are not wrong either. The temp sensor is in the cylinder head- right? It is measuring the cylinder head temp- right? They are only wrong if they think that the cylinder head is hotter than the coolant for more than a split second. The exhaust is, but that's not fluid cooled is it?
I found this extremely interesting. Just thought I'd let you know that... lol
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Old 04-26-2013, 05:54 PM   #7
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Quote:
Originally Posted by erhodes View Post
Hey guys I desperately need some help. I need to know where exactly the coolant temp sensor on a 2005 ford focus ZX5 with the 2.0L duratec is. I was sold a coolant temp sensor today in an effort to solve an issue ive been experiencing. Ford parts calls the sensor in the middle of the head in between the 2 and 3 coils a manifold temp sensor-not a cylinder head temp sensor. but they do not call out a coolant temp sensor. I cannot find any info on this anywhere on the web. Everyone says "they don't have an ECT, they have cylinder head temp sensors." someone please shed some light on this for me
Did you ever figure it out?
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Old 02-14-2015, 05:11 PM   #8
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2005 ZX3 Cylinder Head Temp Sensor

This thread is a bit old, but maybe my experience with this will help someone in the future. My daughter drives a 2005 Focus ZX3 with 175,000 miles. On a zero degree night, she called from school saying the car was overheating, the temp gauge was in the red and the light was on - but she hadn't left the parking lot yet, the car had only been running 2 or 3 minutes. Smart girl for paying attention, being a new driver, and all.

I drove 15 miles to pick her up, checked the radiator and hoses - ice cold - no obvious leaks. I started the car. Within 3 minutes, the dash temp gauge moved all the way into the red and the warning light came on. I checked, the coolant was not frozen. Figuring it was a stuck thermostat or water pump failure, I had it towed to a garage. (Did I mention it was zero?)

Much to my surprise, they called the next day and said that their engine analysis said the cylinder head temp sensor was bad. I didn't 100% believe them, but told them to change it and flush/fill the cooling system, figuring if there was no circulation, they'd find it while draining/filling (and then fix the mechanical problem!)

But, lo and behold. I drove it home, it behaved perfectly after the repair. They were right.

The $350 was a little painful, but I was not looking forward to chasing this down with snow on the ground and a daily high temp of 15 degrees.

In hindsight, it was unlikely that even with no coolant flow, that the engine would completely overheat in 3 minutes at idle on a zero degree night. I didn't try the cabin heater to see if I was getting coolant flow through the heater core. I was too damn cold.

So, moral of the story, these sensors do go bad, they are in the valve cover, and they can fool you into thinking thermostat or water pump problems. The sensor was only $30.00 for the part. Under better conditions, a fairly easy repair.
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