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Discussion Starter · #1 ·
A few weeks ago the temperature gauge in my new/used 2010 focus went into the red part. I checked the coolant level.. It was below the low line. I added coolant to the overflow tank. I had no problems for a few days then the temperature gauge stopped working (doesn't show any temperature change). Now the engine fan isn't working. I know the engine fan was working after the coolant was put in.. Now what part should I be replacing? I'm getting a lot of different opinions. I recently relocated and have no mechanic at the moment but I'm going to need one. Replacement parts range from 27.00 to 300.00...I just want to get the right part..

I figure the fan is not working because its not being told the engine is hot..

Any help would be appreciated.

THANKS!
 

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Moved to General Tech Chat.

First thing to do is look to see if your model has a radiator cap - then open it up & see how much coolant (if any) is showing in there. Top up as necessary.

Some models have a remote reservoir (one place to add coolant), some have a radiator cap 7 overflow bottle (two places you might need to top up).
 

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We could all take guesses, but until you locate the leak it will be just that.. Guesses.

Fill it back up with coolant through the radiator cap and overflow tank, drive it around a bit to get the temp up, sit it in the driveway or somewhere and look for leaks. With you losing that much coolant it should be easy to locate the leak.

--CDM
 

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Fix the leak, but you need a new temp sensor too. You can purchase these from a dealer or from our dealer Village Ford on here. It's easy to replace since it is located in the center of the cylinder head between the #2 and #3 spark plug. I think you have to remove the valve cover to get to it, so you'll need a new valve cover gasket. Depending on the age of your coil-plug boots, you might consider replacing those during this repair as you'll have to remove them. Plug boots last about 80-100k miles, and will cause misfires and bad running conditions.

There is a plug on the cylinder head near the temp sensor. Sometimes that plug will leak. If it is leaking, you'll need to remove that plug, and insert a new plug with pipe thread sealant. Take pics and come back and we'll get into that if you need to.

Depending on how low your coolant was, and the mileage, a leak might not be a big deal. What you thought was overheating may not have been. Those temp sensors tend to fail by giving the gauge an overheating signal. We even had one guy who spent thousands trying to figure out why his car was overheating on the highway when the problem was simply a bad temp sensor and the car was never really overheating. In your case, it is possible that the sensor failed, showed overheating one time, and then went out completely. Change the sensor, and then monitor your coolant level to see if you have some sort of leak. If you do, as Sailor suggested, try the easiest fix first and replace the reservoir cap.
 

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Discussion Starter · #5 ·
Thanks everyone for the response. We could not find a leak. The mechanic I found thinks its the ECT sensor . With my model I could only find it combined with the thermostat. Part number RT1157 (very expensive part) . One dealership did recommend the cylinder head sensor (much cheaper part).

Can someone explain the difference between the sensors in regards to functionality? According to the mechanic (when he was checking for engine codes) the coolant temperature was not properly being transmitted to the gauge.

What does a air pocket in the coolant cause... Will it affect the sensors`..
 

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Cylinder head temp. sensor is the better guess, just because not all of the cars like yours use the coolant sensor in the thermostat housing. In fact, looking to see if it's there is the best way to see if you even have one - parts listings don't differentiate which ones have one (outside of possibly Ford's).

A scan tool or use of the odo. cluster "test mode" can tell you if the CHT (cylinder heat temp) is reporting reasonable temperatures.

Holding the odo reset button while starting, until the engine runs & "test" shows in the display then release gets you into test mode. At that point you can repeatedly press the button to see different items displayed. Engine temp should show in degrees 'C", so don't expect degrees "F".

Good results there show the CHT working, bad result would confirm it's the problem.
 

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Discussion Starter · #7 ·
Thanks for the reply... but would a broken cylinder head sensor explain why the gauge on the dash is not recording any temperatures? So what does the sensor in the coolant do? Based upon the advice... the cylinder sensor might be the problem.. Why would there be a sensor with the thermostat housing... It must have a purpose..
 

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My GUESS is that the models equipped with a coolant temp sensor (whether in the thermo. housing or attached to the radiator) use it for a fan control. I've yet to see any documentation on its purpose, haven't needed to dig into that yet personally. It's quite common to use one that way on other vehicles, hence the guess.

I KNOW that all the ones with only a CHT use that for both temp gauge & fan operation, and I assume that temp gauge stays with the CHT on versions with a coolant temp sensor. (actual engine temp being more important for ECU & warning functions)

So, a bad CHT or connection/wiring to it would result in gauge issues & CEL for lack of engine temp info. to the PCM.

Gauge could have issues itself, or problems elsewhere in communication to it, that's why checking reports from the CHT in another manner was suggested.
 

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The mechanic should have a pyrometer that he can point at the engine to verify its temperature. Because most mechanics won't use the super-handy odometer self-test no matter how often you explain it to them.

You MUST verify that the engine is either overheating or not via another test method before you can make a reasonable call on which parts to replace.
 
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