My truck is a 2001 4 cyl, 2.3 L with 106,000

I will try and explain the best I can. A few months ago my temperature gauge started acting funny, it would literally cool way down when I came to a stop, then back up while I was driving. Sometimes it would work normally. Now it doesn't seem to work and if it does it barely heats up. Sometimes not moving at all even after continuous driving.

I also am getting warm air, but nothing hot coming through the vents like it use to.

How would anyone go about checking for the problem? Would the safe thing be to replace the thermostat first? Thank you.

 

I would replace the thermostat first , then remove the serpentine belt tensioner and spray the inside of it with PB Blaster.
Your problem could just be a slipping belt that does not let the pump circulate the coolant properly.

 

Or could b ur Temp sensor. Check connections first. If that don't help buy a new one. If it doesn't change then return the sensor!!

 

Just about the same problem on my 2000 2.5. The water pumps impellers where gone, so no fresh coolant was going past the sensor. Doesn't hurt to check.

 

I forgot to add a question: Just wanting to make sure but is yours a duratec or lima block? In 2001 they changed in midyear to the 2.3 (some people get confused), if yours is DOHC its duratec, if its SOHC its lima. My 2.5 was a lima and I've seen this problem on a few rangers with that engine with the impellers going bad.

 

I figured out my truck is a 2.5, not 2.3 and noticed LIMA on the engine

I replaced the thermostat, fairly easy. Unfortunately, it didn't solve the problem. The gauge is still jumping around, almost mimicking the RPM gauge. I come to a stop it goes down, accelerate, get up to speed it goes up.

I guess my next plan of action is to check the sensors. I see the two connected to the thermostat housing but have no idea where the other ones are.

The water pump, how can I check to see if it's not working? I tried pinching some lines while idling, and I guess I was supposed to feel a surge, but I didn't feel much of anything.

 

There is no others besides the ones on the thermostat housing. One is for the computer, one for gauge. I think the gauge is the one on the drivers side.

As for the water pump the best way to check it, is to take it out and look at the impellers.

To take it out you need to remove the fan and shroud.
Then locate your lower radiator hose and this goes to a nipple on the block. There are two (8mm i think) bolts on both sides of the nipple/tube. This needs to be removed to all the water pump to come out. Then its just 3 bolts on the actual water pump.

Check this thread I started to show what bad vs good impellers look like. Scroll down to the pics.
https://www.ranger-forums.com/general-ford-ranger-discussion-15/no-heat-replaced-heater-core-t-stat-123357/