I have a 96 F-150 4 x 4, 4.9LY series motor.

My temp guage has been acting a bit dorky the last few weeks and when I went to check the wiring today, The top broke off in my hand.
So, I bought a new one and popped it in and was watching my temp guage sit in the same place after 15 mins at normal operating temp.

Well, I decided to check the Chiltons on my truck and see what the resistence readings SHOULD be at N.O.T. At 212 deg F, I should have a reading of 177 ohms. I had 3100 ohms. Almost 20 times what I should have. Ambient temp readings should be right around 3200 ohms.

I believe I got a bad sensor from the parts store who after 2 phone calls will replace for no charge. My question is other than a bench test how can you tell if you have a bad sensor or could it even extend to a bad guage ??

 

that's pretty much it... ohm it out.

 

Would that account for my gauge not moving any even after running at normal temp after 15 minutes ??
Or is my guage not functioning properly as well ??
Been a long time since I had to ohm things out and I want to make sure this will fix the problem and not lead back to something else.

 

If you are talking about the Engine Coolant Temperature sensor (ECT), that SHOULD read 3,600 (or less..but not less than 1,000) Ohms at operating temperature..and somewhere around 40,000+ Ohms cold.

This at least is what my manual states for the ECT. Now if you're talking about the ACT/IAT (Intake Air Temperature sensor), those resistances are lower. I'm thinking here you might have the two mixed up as to values they should read?

 

I AM talking about the engine cooling temp sensor.
I have been reading and using Chiltons for many years and even the Auto Tech agreed, The values I have are WAY to high.
Maybe Chiltons made a mistake in how they presented and printed the values in the resistence chart.

 

there are 2 sensors for the engine temp. one that goes to the guage and one that is on the y pipe off the thermo housing. the one that controls the temp guage has only one wire the other does nothing for the guage on the dash. i don't know the values.

 

The one I pulled and replaced was on the y pipe or tubing coming off the top of the thermostat housing.
I went to the parts store today to get the replacement for the one I put in yesterday and when bench tested at ambient temp, approx 78 degrees F inside, The ohms reading was 2675. As I held it in in hand and warmed it up, The reading slowly reduced til it was reading around 2200 ohms.
Which means that the sensor I got yesterday was indeed faulty.

 

Hi
I'm a newby here and enjoy reading some of the experiences on this site. Especially since I can relate to some of them. My truck is a 1986 Ford f150 w/300 inline six and a manul trans. I have noticed the dashboard temp gauge needle hovering at the cool side just out of norm. I'm familiar with the two wire sensor on therm, housing but not the one wire sensor for gauge. could someone please advise on approximate location of this sensor. I will try the ohm test I read about here tomorrow to see if the two wire sensor is good as this effects performance.
Thanks, John

 

There are actually two different sensors on the Inline 6.
One is in the thermostat housing/tubing area, and the other is located on the right side of engine block, halfway up the side, and directly behind the exhaust manifolds.

One sensor inputs signals to the computer, The other operates the dash guage.

My thermostat sensor was indeed bad and was replaced. That fixed my computer inout issues.
The sensor in the side of the block was replaced and my guage is now reading just about half way at all times.
I ended up replacing the pigtail that connects to the nipple on the end of the sensor also. Somehow it was pretty well corroded nd making poor contact.