1998 F250 LD 5.4 engine

Any thoughts on this...

temp gauge was pegged at high. When you turn key on before even starting the gauge would peg at full hot. Then when started it just stays at full hot. No movement.

I replaced the sending unit right out in clear view on the manifold.

Now the truck stays on cold and wont move off all the way cold.

That tells me the sending unit was bad but there is another underlying problem.

Before people say the obvious...
These symptoms are going on when the truck is ice cold or normal operating temperature.

I watch the live feedback on this and it will not run over 195 degrees. Temp gauge is dead.

This truck is not in a+++ condition to throw all the money in the world at it. I suggested to customer if the money was going to be so involved and given the rest of the truck is modified potentially an aftermarket temp gauge might be an option.

Having said that are there any sending units from after market gauges that can just be installed into this manifold?

The truck is a 5.4

Thanks for any thoughts on this

 

Well, respectfully, your missing a lot of knowledge about the dash display circuits.
The sensor does not directly connect to the dash gage like old times.
The sensor feeds a solid state chip that converts to an output signal the analogue gage can use.
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The main reason for this is the PCM uses the temperature signal to trigger the Limp mode should the cylinder head temp rise over a certain limit.
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A fault in the gage output part of the circuit may not reflect a sensor change in temperature, short or open with this condition.
You already checked the hot running engine temperature and found it to be proper.
The fault is in the dash system.
A used replacement dash panel may work out, other wise an after market gage will be the answer.
It's about as much work to do one as the other.
To see this system layout, look in a Haynes manual page 12-30.
Good luck.

 

Not arguing but what year was the cut off for the direct reflection from sensor to gauge?

Moreover why when changing sensor did gauge go from solid state hot to solid state cold after sensor change ....if there is no correlation directly on this. Thanks

 

As stated, there is an interface between the sensor and the gage readout.
I cannot tell you with any certainty why a reaction occurred other than the interface saw a difference from your work and reacted as it did.
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I have not kept tract of when a change over began from mechanical.
The change over was a gradual redesign to a full electronic dash from 99 on to accommodate Theft protection system, electronic speedo, electronic Tach, dash diagnostics and additional features as the model years progressed.
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In reality, now many gauges you see are only indicators about the same as a lamp would offer for warnings. But everybody likes to see something that just looks like a gage whether it works that way or not.
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For example the oil gage is just a voltmeter that is set to stop about half scale and does not indicate true oil pressure.
There is a saying from Ford; this is no longer like your Dads truck.
Everything is Logic controlled right down to control of the interior lights.
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Owners of trucks from 2004 up that are accumulating age and mileage are finding it very hard to self repair their vehicles due to lack of knowledge and tools as the year model progress.
There is now electronic throttle control, electronic battery system control and monitoring and many other complex system on board.
Just a sample to let you know ( it ain't getten any easier ).

Good luck.