Oil pressure gauge maxed out

[Dechion]

I seem to be having an issue with my oil pressure gauge. As in, it stays maxed out even with the truck off and the keys in my pocket.

 

Is there anything I can be checking or is my gauge simply shot?

 

I think I read about it being based on resistance, would an open wire cause it to go to max? Or a bad sending unit (shorted) perhaps?

[jimmy21669]

I would try the sending unit. They fail often.

 

They are cheap enough, but make sure you buy the sending unit, not the switch, since you've got the gauge.

[ParadiseMJ]

Replace your oil sender. It's done gone bad.

[Dechion]

Second silly question of the day, whereabouts on my engine (4.0) is my sender hiding?

 

The Chiltons I have access to mentions it but does not give a location or a pic of it.

[ryno56]

it's in the housing right above the oil filter.

[Dechion]

Thanks much.

[HOrnbrod]

Not necessarily the sender. Could just as well be the gauge itself or the wiring between the sender and the gauge. Do this before before running out a buying a new sender:

 

Begin by testing the gauges themselves. You'll need an assistant.

 

For either gauge, the sensors are variable resistors. The range is zero ohms to 88 ohms. Zero ohms, of course, is no resistance, or a short circuit. So, as a rough "go / no go" test, you turn on the ignition (the engine can be running, but be careful where you put your hands. The engine does not NEED to be running, but the ignition has to be on.) Take the wire off one of the sensors. You now have an open circuit ==> infinite resistance. The needle on the gauge should swing all the way to the right. Now find a clean, dry place on the engine block and touch the wire to the block to ground it. You now have zero resistance. The needle on the gauge should swing to the opposite end of the scale.

 

Repeat for the other gauge.

 

If the gauge fails this simple test, you have a faulty gauge, or a break in the wiring between the gauge and the sensor. If you know the idiot lights worked before, the wiring should be good. Problem is, you have no way of knowing whether or not the idiot lights actually worked, because the start-up test only checks the bulb, it can't check the circuit.

[jimoshel]

I believe the ign key has to be on for the sending unit to be in the circuit. If the key is off, then the sending unit is irrelevant. Sounds like the gauge needle is stuck. Try tapping on the cover over the gauge and see if it will swing loose. If that doesn't work remove the clear face and move the needle over to the left, hopefully unsticking it. If that doesn't work, replace the gauge.