Today I was driving my truck for hours and I just so happened to look down and seen my temperature gauge was stuck on Cold, as if I just started my truck
I Just replaced my thermostat last year along with the sensors on it. I turn my heat on and it's blowing really warm air so I can't see it being my thermostat again. You would think if it was my truck would of easily over heated within the hours I was driving it if it were the thermometer not opening.
I know there is another sensor underneath the motor, maybe that could of went bad? Or even just my temperature gauge?
​​​​​

 

The year of and the engine in your Ranger would help
The temp gauge in the dash is hooked to a SENDER on the engine, not a sensor
Not uncommon for sender to come unplugged or to fail

With year and engine model we can tell you where that sender is located
If you find it then unplug
If there is just 1 wire then use a jumper wire to Ground that wire to battery negative and turn on the key, if gauge goes to HOT then wire to dash is OK, replace sender

If its a 2 wire sender, then Ground the Red/white wire to battery negative

If temp gauge still doesn't move off cold then wire or gauge is the issue

Coolant WILL come out when you remove a sender, so you do need to drain some out first
NEVER USE sealant or "tape" on a sender, they need a GOOD ground to the engine or won't work well

 

It's a 2003 with a 4.0L engine

When I replaced the thermostat last year I replaced all the sensors in it when I had it off, I never touched the other one which I think is underneath, so I was thinking it was either that one or my gauge just went bad.
If I feel hear coming out it's safe to drive right? I mean I drove for hours and never had an overheat issue even though I couldn't tell by the gauge

 

2003 4.0l has both the ECT sensor and the temp gauge sender on the top of thermostat housing

The two are seen here: https://howtoreplacefordthermostatho...t-revealed.jpg

Both will have 2 wires
red/white wire is for gauge, it will also have a Black/white Ground wire, test black wire with ohm meter to make sure its a good ground
Test red wire as described above

New just means NEVER EVER TESTED, it no longer means "it works"

Gauge going bad is possible just very very............very unlikely, bad sender or bad connections are 99.9% more likely


Yes, just run the heater to test engine temp now and then, and check coolant level before starting when its cold
Running without a temp gauge is a problem because overheating an engine can do quite a bit of damage fairly quickly if you don't catch it in time
And just FYI, if heater starts to blow COLD that means engine is overheating pull over ASAP!

You can get Bluetooth OBD2 readers for under $25 that work with your smart phone, you can, of course, read codes on ANY 1996 to current vehicle so a good tool to have
But what you can also do is to set it to display Live Data while driving, like engine temp from ETC sensor

 

Okay, is the gauge sender the one that is red? Or is it the Grey one?

​​​​​And I'm sorry, but can you please explain again on how to test and see if it's the gauge or the sender?
At the same time both the sender and the sensor are cheap I could replace both, even though both are only about a year old

 

You need to look are the wire colors, can't tell you by connector color

Yes the sender will have a red and black wire
(sensor will have green and grey wires)

You want to GROUND the red wire, use a jumper wire from the red wire to battery negative
Then turn on the key, engine OFF
Temp gauge should go up to HOT
If so then wire and gauge are OK

If not then wire or gauge is not OK

If gauge went to HOT, then test Black wire, the ground, you can just use the jumper wire between red and black wires
Turn on key and gauge should again go to HOT
If not, then black wire is no longer a good ground

If gauge goes to HOT then both wires are good and sender is bad


Just so you know, the sender is a 12volt resistor
The ETC sensor is a 5volt resistor
So while they look similar they are NOT interchangeable, so make sure you get a SENDER, parts guys will always give you a sensor first, lol

A sensor will often have a cone shaped end, and a sender will have a cylinder shaped end, not always but often, depends on the maker

 

I really appreciate all your help, I'm definitely going to try it now, but just to be clear, when I take the jumper wire I just touch the pin on the inside of the clip(red wire side) to the ground terminal on the battery, then do the same with the other side of the pin inside the connector(black wire)? I never did a test like this other than the starter, wanna make sure I don't short anything

 

You can't short anything, the red wire is the ground for the temp gauge so by grounding it you give the gauge full ground so gauge shows HOT

12volt key on-----------Dash temp gauge--------------------------(red/white wire)------------SENDER-------(black/white wire)--------------Ground(battery negative)

If you unplug the connector on the sender and then connect the red and black wires together, taking the sender out of the loop, via jumper wire, then turn on the key, if BOTH wires are OK then gauge will go to HOT

If gauge doesn't go to HOT then test red wire separately to Ground, battery negative
If gauge does go to hot then Red wire is OK but black wire is not

 

Just wanted to say thanks on the detailed info! I did that test this morning on both wires in the sender and the temp gauge went straight to HOT right away, so I'm going to the store to get a new sender

 

Good stuff

 

So I replaced the sender and warmed my truck up and my gauge is still stuck on COLD. and isn't going up
Could the thermostat went bad after a year? I tested the connections like you said earlier and the gauge went right to HOT
The heat in my truck is also blowing warm too, not the least bit cold, although my idle doesn't want to seem to drop down to the 8-900 range even after I ran for 20min it's staying around 1100

 

Thermostat wouldn't matter, well gauge might read lower than normal but not COLD after 5 minutes of run time

You have the old sender, do you have an OHM Meter?
I would test it to see it is a 12v sender
OHM readings here: https://farm3.static.flickr.com/2191...9979d20d_o.jpg

This chart has BOTH CTS(coolant temp sender), 12volt and ECT(engine coolant temp) sensor, 5volt, OHMs

You can heat up the end of the sender with a match or lighter

OHMs should be 2 digits if its 4 or 5 digits its a sensor not a sender, so would always show cold

Did you check the wires?
Maybe when plugged in they are pushing up so not making contact inside???? just guessing at possibilities

Because gauge went to HOT, both the wire to the gauge and the gauge itself are fine

 

I honestly don't have an ohm reader, when I replaced the sender they were identical matches i made sure to check in store,
Would suck if I have to buy an ohm reader now to see if they gave me a good sender was the only one in stock unless I ordered

 

Is your cooling system full ?

If the sender is not submerged in coolant, it can't measure coolant temp.

 

Same with mine , 2.3 16v duratec 2008 ! Were is de SENDER plug ???! Thanks !