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Discussion Starter #1
I recently got CEL for P0128 - low coolant temp.

Using the dash diagnostic mode, the coolant is running 50-55C which is 120-130F while driving at highway speed and 70-75C in slow traffic. The temp indicator in dash stays rock steady right in the middle and needle hits the middle at normal pace. The dash reading is correct, because the heater only blows warm.

When I idle the car long enough, the heater gets toasty as it should and the temp readout in diagnostic mode cycles between opening up and fan coming on at 232(111C), drops to 212(100C) until it rises to 111C and it cycles back and forth.

I've read this thread already: Low temp problem

Would a stuck open thermostat do this while still letting the engine regulate temp correctly while idling?
Could observing the fluid movement in the pressurized coolant tank or feeling/squeezing certain hoses let me know if the thermostat is constantly flowing? With some cars, you could tell when the stat is open by pressure building up and abrupt rise in temperature on radiator hose.
 

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2006 ZX5 2.0, 2004 ZX3 SVT EE. 2004 ZX3 SVT
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Replace the thermostat. You need the stat with no sensor. I used the one from O'Reilly's. About $35. I remove the passenger side headlight and work through the opening. Takes about 45 minutes start to finish.
 

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Discussion Starter #3
When I pull the hoses WITHOUT draining the coolant, how much of it would spill out? I'd rather save the trouble of dropping the air dam thing again.
 

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2006 ZX5 2.0, 2004 ZX3 SVT EE. 2004 ZX3 SVT
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Put a pan under the thermostat. Just replace what coolant comes out when you pull the thermostat. I don't drain the radiator. There is a hidden bolt on the headlight inside the fender well. You can reach it from inside the engine compartment.
 

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2006 ZX5 2.0, 2004 ZX3 SVT EE. 2004 ZX3 SVT
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The thermostat bolts are accessible without removing parts for access. Yes, it’s tight to slip your hand down along the backside of the radiator but it is possible. I used a short 1/4 extension and a deep well socket and eased my hand into position. Was it easy No! A magnet will come in handy, especially when you drop a bolt that mysteriously doesn’t fall to the floor. The hose clamps can be removed with long needle nose pliers. Of course remove the hoses prior to removing the thermostat. On install be sure to position the clamps exactly as they came out or else you’ll have leaks. Just slip the clamps into the previous grooves in the hoses and adjust them until they sit right where they had been. As far as the amount of antifreeze that will leak out, it is minimal. I used a garage towel to absorb it. When you install the new thermostat be sure to clean up the mating surface and evenly torque the bolts. I didn’t use a torque wrench other than the one in my elbow. If I remember correctly the bolts are 8mm so that calls for a no grunt torque setting. Once the installed is complete top off your fluid level in the reservoir, and check for leaks. Then when you start that old 2.0 on a cold morning you will be smiling because you fixed your no heat issue. YouTube videos show the thermostat replacement by removing parts for access and as I have explained, either way it’s a DIY project.
 

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Discussion Starter #8
Which thermostat do I need and what temperature? There are numerous choices for aftermarket, and even on parts.ford.com, I am seeing two options, one with or without the sensor when I searched by the VIN.

What is the one with the sensor for?

The one here shows 82C/180F, but there was a thread talking about how the one that came out of his car was a different temp than the spare one.

309217
 

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Which thermostat do I need and what temperature? There are numerous choices for aftermarket, and even on parts.ford.com, I am seeing two options, one with or without the sensor when I searched by the VIN.

What is the one with the sensor for?

The one here shows 82C/180F, but there was a thread talking about how the one that came out of his car was a different temp than the spare one.

View attachment 309217
309218
 

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2004 Focus Wagon, Zetec DOHC, Auto
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Sometimes the aftermarket thermostats don't have the air bleed hole in them (or a jiggle valve). I usually drill a 1/8 inch hole in them and position it at 12:00 if the thermostat is mounted horizontally. if it is mounted vertically it doesn't matter whether the hole is located.
 

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Sometimes the aftermarket thermostats don't have the air bleed hole in them (or a jiggle valve). I usually drill a 1/8 inch hole in them and position it at 12:00 if the thermostat is mounted horizontally. if it is mounted vertically it doesn't matter whether the hole is located.
What is used to plug the air bleed hole?
 

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The duratec thermostat is unique. Comes installed in the housing. The bypass for the thermostat is high enough to bleed the air in filling and if you rev the engine to 2500 for several minutes until the thermostat opens with the overflow cap off.
 

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