I just bought this '98 Ranger that seems to be in good condition (for what I paid!) but has been poorly maintained. When I bought it the engine was running great at operating temps, everything seemed good the only odd thing was that sometimes at idle the temp gauge drops to C and only goes back to the middle when you rev the engine. The coolant was in awful shape, brown with lots of rust. No sign of oil in coolant or coolant in oil though. Also the radiator had cracked just before I bought the truck. I pulled the rad, drained, flushed, and repaired. Like I said lots of scale and rust in there. I wanted to change the thermostat and flush the block with a hose but this stupid engine has a plastic thermo housing held on by two bolts w/ 8mm heads and they are rusted/rounded off. Very hard to access as well, I wasn't able to get them off so I flushed the block as well as I could by draining, filling w hose from the bottom and draining a few times. Then I put the rad back on and ran the truck w distilled water until it got to temp, drove it for a few minutes, drained it, filled it again w distilled, drove, drained, filled. I was going to also maybe try some of that rad flush crap. Obviously I'd much prefer to pull the thermo and flush the block directly but I haven't been able to.
Anyway, after all that it worked good, ran at operating temp, etc for a few 10-20 min drives, then the temp gauge basically stopped reading. It stays on cold except if I rev the engine hard it slowly comes up just a little blip. It seems like coolant is flowing because the upper rad hose is hard (maybe a little harder than it ought to be?) and hot but the gauge isn't operating right.
My question is basically, does it sound like I need a new temp sensor or is there maybe a bigger problem going on where scale and rust is clogging up the system and stopping it from flowing properly over the sensor? I'm suspicion that it stopped working right after I tried to flush it. I would imagine if the top hose is hot then the sensor ought to be reading even if it's not perfect but could there be an air bubble or something? My usual technique to bleed the system is just to run the engine with the cap off until it gets to temp and opens the thermo and then let it run another 5 min or so until I don't see bubbling. When I open the rad cold the coolant looks full to the top.

 

What engine size?


Yes, I would swap out ECT Temp SENDER........SENDER not ECT sensor, sensor is used by the computer only, sender is used by dash gauge only, two different parts

Parts store will ALWAYS give you an ECT sensor first time out, so stress S E N D E R, when you ask for the part, they are not interchangable.

The ECT Sender will use a Red/white stripe wire, in 1998 maybe just the one wire, but it was a transition year when Ford was adding a Ground wire for the senders, previously the threads on the sender were the Ground, so only 1 wire was needed

 

Wellll sounds like I just got back from the parts store with the wrong part! Thanks for letting me know that would have taken a while to figure out. I'll get the sender tomorrow and try that. It's a 2.5L

 

Picture for 2.5l, 1998-2001, here: https://www.ford-trucks.com/forums/6...er-sensor.html

But check wire color to be sure, they may have it mislabeled in picture

 

Gauge is working great with a new sender. Thank you for clarifying the sensor/sender, that was very helpful. You're right about the parts store really wanting to sell you the sensor!

 

Good work

Thanks for the update and FIX