Temperature sensor, and coolant sensor

My truck runs at normal temperature, but the gauge barely reads. Therefore, I know the gauge is getting some juice.

I also know I am running rich. I just replaced the engine, and I have the same rich issue I had before with the old engine.

I have a pretty good feeling my coolant sensor is out, the one located next to the thermostat. I feel this is what is causing my richness.

My question is this. Does the coolant sensor also run the gauge in the truck? If not where is the temperature sensor located ( the one that controls the gauge)?

In short, is there two sensors, or just one?

Thanks for the timely responses,
Ross

There are two coolant temp sensing devices on all fuel injected engines.
1. Coolant temp SENDER, for dash board gauge, it has a 1 wire connector
2. Engine Coolant Temp(ECT) SENSOR, for computer(PCM), it has a 2 wire connector(this operates the electronic "Choke mode")

To test SENDER circuit, find it , then disconnect it's wire/connector, turn key on, needle should move to below Cold, now Ground the 1 wire connector, needle should go above Hot.
If this happens then gauge and wire are good.
If you don't get full range movement of needle then gauge or wire is the problem.

SENDER can be tested with OHM meter, ground to connector should read about 80ohms-cold, 10ohms-hot, these are "abouts", as long as ohms drop steadily as sender is warmed up it is probably OK


ECT sensor works pretty much the same(high ohms cold, lower ohms warm) but computer sends 5volts thru the sensor, so 2 wires are needed, as the ohms go down(coolant is getting warmer) the voltage going back to computer gets higher.
Computer runs Open Loop(choke mode), so higher idle and richer mix, based on ECT sensors voltage return, as voltage goes up idle goes down and fuel is leaned out until Closed Loop temp is reached and computer then uses the O2 sensors to set fuel trim.
O2 sensors can not work below 650degF, so are of no value when engine is cold, this is why almost all O2 sensors are "heated", so computer can use them ASAP, but it still takes a few minutes for exhaust temp to warm them up.


Ford uses 192 or 195degF thermostats, this is because the best MPG and best oil cleaning happens when coolant stays above 190degF.
Some misunderstand the purpose of the t-stat and use a 180degF or even a 160degF model, "running cooler" is not good, costs you money in gas and the oil temp doesn't get hot enough to burn off moisture(condensation) and blow-by(fuel) contamination, so bearings wear out faster.
You are not doing your engine(or your wallet) any favors by lowering the operating temp, quite the opposite.

So if you are running "cooler" and are not sure what t-stat is in there I would replace it with 192/195degF model just on spec.
I think most Ford temp gauges have 210degF as the 1/2 way point, so running just below 1/2 would be normal.

Thanks, RonD, for the informative post.

It cranks up fast when it is cold, but when it is warm it takes a couple of turns. I also smell rich mixture, though I am unsure of how rich it is. It also has a slight stall at times.

I done checked the fuel regulator (hope that is the right name for it), and changed the O2 sensor. I am still having the same issues as the old engine though.

Even though at this point I am parts changing, I figured it wouldn't hurt for the cost and the new engine. I just know I got to get that rich mixture down.

Thanks again for the reply,
Ross

Could be the ECT sensor.
When you first turn on the key the computer comes on and one of the first things it does is to look at the power coming from the ECT sensor, 5volts in and only 2volts back means cold engine so run it RICH.
Now if for some reason the ECT sensor has high resistance when first powered on then even if engine was warm computer would think it is cold and run it rich, so cranking would be a hard start, and once running the ECT sensor quickly goes to low resistance(warm engine) so all is well, except for hard starting warm

I would check the ECT sensor connector, a little corrosion on there could cause that.

Thanks again RonD.

I just now changed the ECT, and I will get to drive it tomorrow. I did see ever so slight corrosion in the connecter, but it really didn't look like enough to make a fuss about. If I continue to have the same problem, I will look into cleaning it better. I honestly didn't have the time tonight to get to deep into it.

The gauge sender went out, but now it works too. This is why I figured it would be good to change the other out, other than the issues I was having. Also the truck is old, I don't think it hurts to change something this cheap and vital to proper engine function. This was the reasoning for my post. I did not know if it came as a single unit, or two units.

Rep was added, you have been a great help. Keep up the great informative post. Post like this make the site worthwhile.

Thanks again,
Ross