Radiator fan

Tiny
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  • MERCURY TOPAZ
92 Merc topaz, 4 cyl, over 200k.
recently replaced thermostat. Fan on radiator has not been working. While warming up engine to finish filling radiator after thermostat replacement, I unpluged the Coolant tempature sensor from the thermostat housing and the fan turned on. It has not ran in over 9 months.

How to I determine if the tempature sensor is working correctly? IS what happend a good indication that the sensor needs replacing? I have to do this repair on the cheap, as I am out of work, due to an accident at work.
Thanks.
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Tuesday, October 23rd, 2007 AT 3:42 AM

9 Replies

Tiny
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You need to check hot and cold look below


http://www.2carpros.com/forum/automotive_pictures/12900_0900823d8015231b_1.jpg

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Tuesday, October 23rd, 2007 AT 5:04 AM
Tiny
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Well, if I understand your chart correctly, when the car is warmed up, the resistance should be close to zero.

Well when we unpluged the sensor, the fan kicked on.
Electricly speaking, when I unpluged that sensor, the ohms reading across the PLUG unit itself should have been maximum, or infinate as there would be nothing connected to the 2 plugs in the wire harness.

And according to your chart, the higher the reistance, the colder the engine.

This makes me think the problem is not the sensor, but maybe the controller box.

Does that make sense? Thanks for your reply.
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Tuesday, October 23rd, 2007 AT 11:36 AM
Tiny
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If the CTS checks out good in hot and cold readings while unplugged. Then the problem is coming from somewhere else could be the computer or another temperature switch.
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Tuesday, October 23rd, 2007 AT 4:37 PM
Tiny
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IS there another temp switch on the thing? I finally got around to testing it, and according to the chart above, it checked out ok.

Guess im going to have to take it in for a scan.
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Monday, October 29th, 2007 AT 12:14 PM
Tiny
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According to my resources it has a temperature switch on the goose neck /thermostat housing 2.3/3.0L
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Monday, October 29th, 2007 AT 2:21 PM
Tiny
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Thats the one I am checking, its right next to the thermostat.
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Tuesday, October 30th, 2007 AT 1:59 AM
Tiny
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That's why were not getting anywhere the temp. switch is for the gauge, the CTS is for the fan thru PCM and relay. Look below no.23 CTS


http://www.2carpros.com/forum/automotive_pictures/12900_cts_1.jpg



and get back to me, we wasted valuable time
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Tuesday, October 30th, 2007 AT 2:09 AM
Tiny
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I couldn't quite make out what item you ment by the drawing, I even got a copy of it to enlarge, and still could not make it out.

THIS is what I have checked out based on the information posted here so far.


http://www.2carpros.com/forum/automotive_pictures/110024_n1_1.jpg

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Wednesday, October 31st, 2007 AT 1:45 AM
Tiny
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Im not an automotive mechanical genius as a tool and die machinist, however, I have been doing electronics since I got my first ham radio licence at age 14.

According to the first response above, the coolant tempature sensor is basicaly a variable resistor.

The plug unit, that is the wire harness that attaches to the sensor, is compeating a circut, that is being monitored somewhere.

According to the chart, as the tempature of the engine goes up, the resistance measured should go down.

I.E. If I unplugged the unit and put a jumper wire into the plug, there would be ZERO ohms or ZERO resistance. Resulting in a "closed circut" or a "short". Meaning there is supposed to be a load of some kind there, but there is nothing, thus a short has occured.

Again, according to the chart, when the engine is cold, the resistance should be high. Taking that jumpe wire out, should give me infinate or maximum resistace. Since nothing is plugged into the sensor wire plug, there is no current or voltage flow, thus this results in an OPEN circut.

The Fan is supposed to kick on ONLY when resistance is low or non existant, and current or voltage in the crcut is still able to flow thru the circut.

Again, when I unplug the wire harness from the temp sensor, (an open circut) the fan turns on regardless of the tempature of the engine.
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Wednesday, October 31st, 2007 AT 3:46 AM

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