1999 Ford Ranger 6cyl, 4.0, Replaced the Instrument Cluster Panel TWICE and I get the same thing. The 2 Instrument Cluster Panels came out of an Explorer. The Salvage Yard showed me on the computer that they were an exact fit (guess I have a question about that).
It starts off just above :"C" when I first start in the morning and within abt 15 mins will go to "H". This happens everyday and everywhere I go.
I have changed out the 2 housing sensors, thermostat, radiator cap and coolant.

Any ideas from this "Shadetree Mechanic?

Thanks in advance.

 

I guess first question is............is engine overheating?
Is overflow tank full or bubbling?

1999 Ranger will have 4.0l OHV, and a GEM module for "body" electrics
It has 2 temp sensing devices on the front lower intake of the engine
A 2 wire ECT sensor, used only by the computer
A 2 wire Temp Sender, used only by the dash board gauge

The 2 wire Sender is the one you need to test, it will have Red/white stripe wire and a Black/white stripe wire.
Remove it's connector
Get a Jumper wire and connect it to the Red/white stripe wire by pushing it into the connector

Turn on the key, engine off
Temp gauge should be below C on the gauge since wire is unhooked
Ground the other end of the jumper wire to the engine, or battery negative
Gauge should move up all the way to H or above

If both of these things happen then replace Sender, make sure you get a SENDER not ECT sensor.

What years were the explorer dash boards, and do the other gauges seem to work OK?

 

Hello RonD
the overflowtank is full, not bubbling.
On my 4X2 1999 Ford Ranger (6cyl 4.0 OHC), there are 2 sensors (I can see them on the manifold, 1 has a single wire while the other has a 2-wire connector. I'm going to change out that 2-wire sensor since the one I have in there, I got from the Salvage Yard too. I will follow-up with you on when I put that part on and test it. Thank you again for your technical expertise.