How to check an oil pressure gauge?

[surflvr911sc]

My dad’s oil pressure gauge is pegged at the top. I replaced the sender but no dice.

It’s stays pegged w/ the wire connected, disconnected, and grounded. My next step will be to check the wire continuity between the sender and the gauge but I want to know how to check the gauge to make sure it’s working. TIA

[Rot 911]

If the gauge is still pegged after all that you either have it grounded somewhere else or the needle is stuck. I would first tap on the glass to see if the needle will drop. If that fails, pull the gauge and pull the oil pressure wire at the gauge.

[surflvr911sc]

Yeah, that’s what I’m afraid of. When the ignition is off the needle falls back to zero so I don’t think it’s stuck.

Little more info- On the back of the gauge, the three red/blue wires are connected to the + terminal, the one brown wire is connected to the – terminal, and the green/red wire is connect to the blank terminal. This seems correct to me but I wanted to confirm.

[jazzbass]

There are three potential problems:

1. Bad sender
2. Bad gauge
3. Bad wiring between the two

Now, on my car, the pressure sender works between (I think) 10-180 ohms. Lower resistance = low presure, high resistance = high pressure. Since his gauge is pegged, there is a good chance either his sender is bad (completely open) or the wiring is bad (again, open).

In any troubleshooting, I try to isolate each variable and test. Since this is you're dad's car, and you also have a 911 (presumably with a working pres gauge and around the same vintage), this should make testing easy.

First, pull the sender wire (in the engine compartment) in his car and ground it. Does the needle go to 0? If so, the sender is bad. If not, it could be the wiring or the gauge.

Try putting your gauge in his car. Does it work? If so, #2 is the problem and #1 and #3 are not. If not, it could still be any one of the problems. If your gauge does not work in his car, verify his gauge works by putting it in your car. If it does work, #2 is OK.

Next you need to eliminate #1 or #3. Try testing the resistance of the sender and compare to yours. I think the range should be somewhere between 10-180 ohms (can anyone confirm this?). My guess is that its open.

[Joe Bob]

When I put the oil gauge in the 356....the gauge pegged with 12v and ground....did not read right until the sender was hooked up. When I pulled power and left sender and ground it was at zero....

[pbs911]

What MikeZ said. The power and ground are properly hooked up but it is not reading the sending unit.

[Early_S_Man]

Ryan,

If you hook up a 200 Ohm or 500 Ohm potentiometer with center contact to the gauge input terminal and one of the end terminals to ground ... you should be able to sweep the pot from one end of its' range to the other and the gauge should sweep full range! The test can be done either at the engine, or at the dash!