Ok. First post ever - used this forum for a long time. I appreciate all of you guys' contributions. I'm stuck on a problem now and can't figure it out.

Temp gauge stays low all the time. Starts out below the C and will only move above the very first line C(.I..........)H <----like my diagram?

Initially found a Ford TSB for temp sending unit/switch (to gauge). Replaced sending unit. Gauge worked fine for about a month. Replaced sending unit again. Gauge worked fine for about a week. Replaced sending unit again. No change. Did I get a bad part? Replaced sending unit again. No change. -----This is an 8 dollar sensor so I'm not worried about the cost (obviously). Its just a pain to keep doing this. I even tried cleaning up the threads that the unit goes into in case it was a bad ground. Nothing.

I'm 99.9% sure I don't have another problem - so correct me if I'm wrong. And I don't have access to an infrared temp gauge or a scan tool to ck for actual temp.
Why do I not think I have another problem?
Radiator hose has no pressure upon startup, and becomes pressurized after awhile - tstat is opening and closing.
Blocked the radiator for a few minutes after the engine was (or should have been) hot. No change in gauge.
Directly grounded the sending unit wire. Gauge pegs to HOT. Circuit up to the sending unit is fine.

Am I just getting bad parts all day?? I've yet to get one from Ford. They've all been aftermarket. Any other ideas?? Any input anyone has would be awesome.

 

Is it something you can live with?

I do, in my 1990 Bronco.

Get a Ford part?

 

I can live with it I suppose if I know for sure that the temp is fine. But if I ever do have an issue, I won't know till it's too late.

My next step is, yes, get the ford part, see if that helps. And find someone with either an infrared gun or the scan tool to verify that I'm good.

Other than that, I was just hoping I'd missed something...
Thanks for posting though!

 

I was looking thru my Service manual and it has a chart with ECT sensor voltage to temp conversions. Maybe you could find something similar.

 

Edit: Welcome to FTE.

Good trouble shooting.

From the test you did by grounding the temp gauge wire, I agree it sounds like the wiring & gauge are likely ok.

After the gauge stops working again, check between the sensor metal Body & a clean unpainted spot on the engine head for zero ohms, so your certain you have a good ground connection between the sensors threads & the engine head, if your using ptfe tape as a thread sealant. If the ground connection is bad, use less tape, 3-4 turns, or use a liquid pipe thread sealant that'll squeeze out between the threads, so they'll make good physical contact & electrical connection, Permatex/Loctite make a good liquid pipe thread sealant product, thats avaiable at most autoparts stores.

If the ground connection is ok, at the sensors electrical connection, measure it's resistance to ground.
Engine fully cold = 75 ohms, Engine fully warm = 10 ohms.

If the sensors resistance value isn't right & you know the ground connection is good & you've been buying them from the same store, maybe you got into a bad aftermarket production lot????

So, I'd speek to the store manager to let him know whats going on, get my money back & shop at a different chain store, so your likely getting a different brand & vendor, or consider forking up the gold for a Motorcraft sensor.

More thoughts for consideration.
Let us know how what you find & how it goes.