i recently got a 90 F250 5.8L 4x4. the previous owner installed aftermarket coolant temp gauge and oil pressure gauge. both mechanical. only the temp gauge was hooked up.
i tested my oil gauge by grounding it and turning on the truck. nothing. ok, gauge is bad. assumed the same for the temp gauge.
got a cluster from the junk yard with a tach this weekend and installed it.
now, my oil gauge goes full negative pressure. as in it moves to the left once the truck is turned on, not running. it does this when i ground the wire for it also. what does that mean?

i also replaced the sending unit for the temp gauge with a new one for the stock cluster gauge. it doesn't do anything. how can i test this gauge?

 

I do not know if this is the same for the 5.8 as it is for the 4.9 300. I have two temp sending units. One is at the front of the engine off the thermostat housing which is for the ECU and I have another on the passenger side above the starter which is for the gauge cluster. I am sure someone with more 351 experience can chime in out it.

 

yes, there are 2 sensors for the temp on the 5.8l. one is for the computer, which in the thermostat housing, and the other is for the gauge. its located on the front drivers side of the the intake manifold, next to the distributor. i replaced the one for the gauge. it has a threaded stud and single wire connection where as the other has a 2 or 3 wire connector.

 

The temp sender for the gauge has only one wire and it is a push on type wire.


/

 

Did you make sure to get a compatible instrument cluster? While most clusters from the 92-96 range can fit and the electrical connectors will work, the wiring may be different depending on what year you got it from. Some will work with no changes, others need to be re-pinned.

 

He has a 1990 and not the 92-96 range.

 

DOH! I certainly missed that one...I'll leave it there for someone else if they stumble across this

 

so i know which sensor goes to the gauge and that is the one i change from the aftermarket mechanical sender, to the factory electric one wire sender. i let the truck run for 5 or so minutes and the gauge never moved. i am asking is there a way to test the gauge to see if it is in working condition, similar to testing the oil pressure gauge?
the cluster came out of an '89 just to put that out there. all other gauges work aside from those 2 that didn't work previously.

the other thing i thought of today was that there might not have been enough coolant in there to submerge the sensor completely.

 

no one know how to test the coolant temp gauge?

 

Only thing I can think of in how to test it would be to use a power supply. You would have to figure out the signal voltage from the sending unit and then locate the pins in the cluster and send it to the that gauge. Not something most people would have readily available to try. I would think.

 

Grounding the coolant temperature gauge wire should peg the gauge full hot.

 

ok, thanks, i'll give that a try.