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temp sensor

Old Dec 16, 2006 | 05:10 PM
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temp sensor

Where is the coolant temp sensor located on an 89 f250 351w? And how you could test to see if its working, im guesing with a ohm meter?
 
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Old Dec 16, 2006 | 05:19 PM
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The location of the sensor is in the middle of the intake on the front in a tee, just behind the thermostat cover and upper rad hose. Apparantly it is facing towards the back of the motor, and on a 302 it faces towards the rad. To check and see if it is working, take a voltmeter and measure the volts on the green/white wire coming out of the sensor. At operating temp it should be between 0.6 and 0.8 volts, and while warming up it should be steadily dropping from around 5 volts to the 0.6-0.8. I checked mine with a lighter after i had it removed, and i started to melt it before it changed. The new one i got was all metal, the stock one is plastic, and the volts started dropping right away after i hit the lighter to it.
 
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Old Dec 16, 2006 | 05:43 PM
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Ok thanks for the reply. Ill probably replace it tomorrow if I test it and its not working.
 
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Old Dec 18, 2006 | 05:19 PM
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Ok replaced that today still no response. I went to check the gauge itself but it goes into its "resting position" when the ignition is off then when i put the key to the first notch the gayge goes all the way left. So im thinking its not the gauge. I couldnt remove the gauge cluster because it wont come out far enough to unplug the connectors. I was goin to test the voltage to the gauge but I cant get to it as the cluster only moves forward about an inch and a half. If anyone has any other ideas let me know.

Thanks,
Jason
 
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Old Dec 18, 2006 | 05:23 PM
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o and how would i test volts? or do you mean ohms? because the sensor is just supplying the gauge resistance as the temp goes up or am i wrong. I held a lighter to the old one and the ohms went from like 27 - .7 So im guessing the old one was fine. At this point im lost. I replaced the one above the pump facing me so im guessing that was the right one but ive been wrong 1 other time in my life so i could be again. wow ok well if anyone has any ideas let me know please.

Jason
 
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Old Dec 18, 2006 | 06:07 PM
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ok there are two "sensors". One is better termed a switch which is a one wire set up and only runs the gauge. The other one in the tee that i was telling you about runs the computer. The one for the gauge is going to be resistance as the gauge measures the difference in resistance. The one for the computer uses voltage like i mentioned. Are you having a problem with the guage or your truck running oddly?
 
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Old Dec 18, 2006 | 06:22 PM
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Ok well the one i put in had two wires so im assuming that one is for the computer. My gauge currently does not register the temp. It just stays as far left as it goes but then creepes right when the key is off. So you think the problem is the other one and i just replaced the wrong thing?
 
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Old Dec 18, 2006 | 06:31 PM
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Do you know for sure that the truck reaches operating temp? if not i would look into a thermostat before i would start blaming the gauge. The gauge creeping right after the key is off is fairly normal for a guage and wouldnt be too concerned about that unless the truck is reaching operating temp, and then for the price of the switch for the guage i would change that before i start blaming the guage itself.
 
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Old Dec 19, 2006 | 05:11 AM
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Well it is reaching proper temp and i just installed a new thermostat three days ago. I cant seem to find the part that you are talking about online. Also i wasnt concerned with the gauge creeping because thats what they all do i was just saying that because the fact that it moves on startup tells me that its working just fine and is probably that part you mentioned but i cant seem to locate it online. What is it name again a switch?
 
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Old Dec 19, 2006 | 08:33 AM
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The gauge sender is what you are looking for. It is just forward of the cylinder 5 runner on the drivers side of the lower intake manifold. It is a one wire sender. You can test the gauge by grounding the wire from the sender and when you turn the key on the gauge should go to full hot. If it doesn't, there is a problem with the gauge.
 
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Old Dec 19, 2006 | 09:38 AM
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Some call it a temp guage sending unit, others call it the coolant temp switch. Depends on your auto parts store. As long as you mention its the one for the gauge then you should be fine and make sure its a one wire hook up. Like EPNC said, its on the driverside front part of the intake manifold.
 
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Old Dec 19, 2006 | 01:21 PM
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ok thanks ill get the part soon
 
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Old Jan 30, 2007 | 03:42 PM
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Originally Posted by EPNCSU2006
The gauge sender is what you are looking for. It is just forward of the cylinder 5 runner on the drivers side of the lower intake manifold. It is a one wire sender. You can test the gauge by grounding the wire from the sender and when you turn the key on the gauge should go to full hot. If it doesn't, there is a problem with the gauge.
i did this and it didnt peg on hot so its the gauge,so ho do i fix this?
 
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Old Jan 31, 2007 | 05:38 AM
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replace the guage which will require more work getting to it then actually replacing it
 
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Old Jan 31, 2007 | 06:54 AM
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It could be a problem with the wire also, if you want to check that before replacing the gauge. Either way is going to require you to remove the gauge cluster from the dash, which isn't very difficult. Take off the headlight and windshield wiper *****, pull off that trim piece, take out the screw just under the steering column securing the trim piece on the right side of the column, then take out the screws holding in the upper trim piece, and finally remove the screws attaching the gauge cluster to the dash. Unplug the speedometer cable (squeeze the connector a certain way) and unplug the two wiring connectors. Figure out which wire controls the malfunctioning gauge and test continuity between the gauge cluster connector and the sender connector. If the resistance is low, replace the gauge (or the whole cluster, whichever is easier to find).
 
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