temperature gauge drops below cold when running

[trozei123]

this issue has really got me stumped. my 92 xlt's temp gauge is going crazy. when i first start it up, the temp will slowly warm up just fine. when it is warm (and i am guessing when the thermostat should open), the gauge bounces down, and finally settles below the cold line. i have read that these engines should be burped of all air. i have squeezed the upper hose several times, when engine is off and is running. gauge still bounces. i even thought the gauge was bad, so i got my hands on a new one. no dice again. how can i get this issue fixed. is this a possible issue of why my fuel economy isnt so great?

 

[natenkiki2004]

I'd throw a new thermostat in, preferably a Stant SuperStat.

 

[Number4]

My '94 for over a decade has never reflected proper temperature. My dad owned it before me and always took it to Ford. I don't know how many times they replaced the temp sensor.

Never been resolved. Doesn't go below cold, but I'd be willing to bet it's related.

 

[larrydd999]

My '94 has done almost the same thing occasionally since I bought it over 3 years ago. In my case the gauge doesn't move very far, then goes back down. I've replaced the sender and checked the wiring without finding anything. It has to be a wiring issue, but I just haven't found the right connector yet.

 

[Centaurious]

You have a couple of possibilities why your gage is not steady.

1) Electrical. You may have a bad electrical connection between the gage and the sending unit. You have 2 sending units, one for the gage and one for the ECU. The gage plugs into the inside of the cluster and these connectors secure the plastic circuit sheet on the back of the cluster. The main connectors also press against the circuit sheet. Cleaning these connections may help. You can see if the connector at the sensor is good and making reliable contact.

2) Coolant. The sensor only works when coolant is in contact with it. If it has air against it it will not read correctly. Installing a flush kit in the heater return line will give you a high point to fill at. If you are not seeing the level in the overflow container go down after the engine cools off you have a air leak. A large drop in coolant is normal after replacing the coolant as the system purges air into the overflow and sucks coolant back into the radiator. If the level keeps dropping after 4 or 5 heating/cooling cycles you probably have a coolant leak.

Even something as simple as an air leak at the nipple under the radiator cap can allow air into the system and cause the gage to move from coolant bubbles.

 

[trozei123]

i know this is a silly question (i believe the only dumb question is the one you dont ask), but how do i use a voltmeter to test the ect? i have access to one, but have no idea how to use it. also, where is the ect? my haynes manual doesn't have a picture that shows where it is.

 

[the_don]

keep in mind there is two temp sensors one for the computer and one for the guage, my guage would come up a little then drop back to "cold". i had hunted and hunted for the problem, then i replace the single wire temp sensor behind the thermostat housing and it word fine since.

 

[natenkiki2004]

ECT is the 2-wire round connector & sensor located directly below the throttle body. You use the ohm setting on the voltmeter to probe the 2 pins in the sensor with the connector removed. The resistance through the sensor indicates the temperature of the coolant and thus the temperature of the engine.

Here's a chart:

Keep in mind, the gauge you see on the dash has nothing to do with the 2-pin ECT sensor. The dash gauge uses a smaller sensor with a single wire that's located near the ECT but closer to the passenger side.