Temperature Gauge Issues
 

Hey Everyone!

I'm new to the forum and to the Ranger community. Looking forward to getting to know you all!

I recently picked up a 1998 Ranger Splash 4x2 with a 2.5L 4-cyl engine and I'm having some issues with the temp gauge not working. What I find odd is that when the truck is completely off, the gauge creeps up to the middle between C & H and stays there, regardless of the temp of the engine. As soon as I turn the ignition to accessory mode or start the truck, the needle drops below C and does not move whatsoever, even after the engine gets warm. This model has a temp sender and temp sensor that both screw into the thermostat housing, so I went ahead and replaced both to no avail. I took the connector off of the sender and plugged a wire between both prongs and the gauge moved to full hot, so I *think* this means the wiring and gauge is okay according to some other posts that I've read.

Can you guys think of anything that might be causing the gauge not to work?

Some additional info that might be helpful:

• 166k miles
• The cooling system has quite a bit of rust so I've performed a couple of flushes so far and have also replaced the thermostat. My heat stopped working after one of the flushes, so I'm also trying to figure that out.
• The upper radiator hose does get hot to the touch once the engine gets up to temp, so I know coolant is flowing through the block.
• I don't recall the temp gauge working at any point.

Thank you in advance for your help!

If the gauge went to HOT by grounding its wire and key on, then sender is bad, new or not

Sender is a 12volt unit
Sensor is 5volt unit
So not interchangeable

You can have sender out and connected, then heat it with a lighter, see if gauge moves, lighter/match is 600deg so just needs a little warm up, lol, coolant is 200deg when warmed up

Remove either heater hose at the firewall when refilling the system, it lets the air out of the engine side of thermostat
Its also a good idea to reverse the heater hoses at the firewall to back flush the core, do that every 2 years

You can remove heater hoses and back flush the heater core with garden hose, to make sure it has good flow, they do get clogged up when you do a flush on engine/rad side, any debris can go into core and then can't get back out thru the smaller passages
Feel the heater hoses as engine warms up, the hotter one is now the IN from engine, mark it
You want to back flush by sending water in on the current OUT hose port in core, that will push out any larger bits

Heater cores have no flow direction from manufacturer, user decides direction when hooking up the hoses, or reversing them

Hey Ron,

Thanks so much for the suggestions. I took the sender out while it was still connected and touched a flame to the end of it. Sure enough, the gauge started creeping up into the normal range. Do you think it's possible that my truck is running so cool that it never gets into the normal range or do you think there might be some issue with the flow of coolant across the sender? When I replaced the thermostat, I put in a new Stant 45990 192-degree if that's helpful to know.

I was also thinking that the heater core may have gotten clogged after one of my flushes but your insight has further validated that thought. I'll give your method a shot over the weekend to see if that solves the heat issue. I'm currently running some Thermocure through the entire system to see if I can get some more of the rust out, so I'll manually flush the heater core after I drain that.

Thanks!

Yes, it reads like there is air in the system or flow at the sender is blocked/limited, air tends to get trapped at high points when refilling and heater hoses are high points, so removing one will let the air out
If enough air is trapped in a heater hose then it creates an "air dam" that water pump can't clear, and sender is usually located near the heater hose coming out of intake, so with no flow thru the heater hoses you get no heat in the cab and no temp sender warm up

192deg is the correct thermostat temp rating

Hey Ron,

Apologies for not following up on this sooner – you were absolutely correct. After completing my final cooling system flush and refilling with coolant, I jacked up the front of the truck and let it run for a bit with the radiator cap open so that any air that was trapped in the system could be burped out. After that, I started getting heat again and the temperature gauge is now working.

Thanks again for your help!