Bench test oil pressure gauge

[nboost]

Is there any way to bench test the oil pressure gauge itself? I hooked up a mechanical one & it has good oil pressure. I replaced the sending unit & checked wire continuity & it’s good. My only guess is the gauge. Any other thoughts on this? All the other gauges are working.

 

[Jdgephar]

Rig up an air line from a compressor and measure the resistance at different air pressures? That's probably how I would do it.

Oh, sorry, that's the sending unit. For the gauge, take the wire direct to ground or open circuit to sweep the gauge. Wire off the sender (no ground) should be 0 psi (actually lower, the needle shouldn't move). Direct to ground should be high PSI. Just don't hold the wire to ground for too long, just enough to see the needle sweep all the way over.

 

[DirtDonk]

But I think they’re referring to the electrical gauge from the factory.

 

[Steve83]

Assemble it & apply a known pressure.

But it really doesn't matter if it's accurate - it only needs to be relatively precise, meaning that it goes to the same position every time a particular pressure is applied. That's why later oil pressure gauges have no numbers; the number doesn't matter. You're not looking for any particular number - you're looking for a change from where you usually see it under the current driving conditions. If you're idling in hot weather one day, and it's ~1/4-scale, and the next day it's 0 or full-scale, there's a problem. But if it's still ~1/4-scale every time it's idling hot, the actual pressure number is irrelevant and just a waste of time & effort trying to read the tiny numbers. Same reason the fuel gauge doesn't have numbers.

 

[jamesroney]

Is there any way to bench test the oil pressure gauge itself? I hooked up a mechanical one & it has good oil pressure. I replaced the sending unit & checked wire continuity & it’s good. My only guess is the gauge. Any other thoughts on this? All the other gauges are working.

Of course there is.

But the question is more about what's actually happening. Is your gage moving at all? Or pegged full? Or stuck somewhere? Regardless, if you want to test your oil pressure gage, you need to understand that the instrument consists of an Instrument Voltage Regulator, a Movement, (also named the Gauge) , and a Sender. It is rare that anyone wants to test their "gauge" when they really want to test their "system."

But you need to know that the oil pressure gauge runs at 5 Volts of pulsating DC. And it drives that 5 Volts thru the instrument, and uses a variable ground at the block. The Ford resistance values are 10-73 Ohms. So a 10 ohm resistance gives you "max" and a 73 Ohm resistance give you "min" The halfway point is 24 Ohms, which is a common resistor value, but you need a 6 watt power resistor so it's harder.

@Jdgephar is giving great advice if you want to test the instrument function. Ground the sender, and watch the instrument sweep to "max." But if you want to test the accuracy of the instrument, You want to test it at 23-25 Ohms. I use the tail light filament from an 1157 incandescent light bulb from a tail light socket. The tail light fllament is about 23 ohms, and will handle the power output of the IVR. So if you put the 1157 bulb between the sender wire and ground, it should go exactly 1/2 way.

 

[nboost]

It doesn’t show any pressure at all

 

[Steve83]

It doesn’t show any pressure at all

Then start by grounding the sender wire with the key in RUN, which is the easiest to do. If the gauge still doesn't move, check for a pulsing voltage at the gauge terminals. If it's not getting electrical power, it can't move.