Test an oil pressure gauge?-gctid821645

[wgander]

My oil pressure gauge pegs to high as soon as I turn on the ignition switch and stays there while the engine runs. The only time it moves is when I turn off the key, and it drops back to zero. The engine has always run at 40 PSI. The wires on the gauge are in a molded plastic harness that can only be put on one way. I replaced the oil pressure sender, but that make any difference. I was going to wire the gauge directly to the sender to see how it reads, but don't know how. The gauge has several posts in addition to one for the light. One is marked Ground but I don't know what the other two are for. There's only one wire on the sender - blue.

[Ruffryder]

(S) LT BLUE - sender signal wire

(I) PURPLE - Ignition switched or 12VDC +

[wgander]

So, can I just go to the engine , connect the sender to the gauge, the gauge to battery positive and negative?

I'd expect no reading until I start the engine, then 40PSI.

[Ruffryder]

correct
..........

[SuperiorDiver]

you could put a mechanical gauge in temporarily, or check the sender with an ohm meter to see if it is at/near zero ohms with engine off. I would guess the sender has failed.

[Sunbird]

A quick test would be to disconnect the wire at the sender. Turn the key on and if the gauge reads zero this tells you the signal wire from sender to gauge is not grounded. If the gauge reads zero replace the sender. If the gauge does not read zero with the sender disconnected you have a wiring issue.

[builderdude]

"wgander" post=821645 wrote:
My oil pressure gauge pegs to high as soon as I turn on the ignition switch

Sounds like it's grounding out, what does it do if you disconnect the sending unit?

[wgander]

I'd have to put it back in the boat to be sure but I think It reads 0 until I turn on the power, then it pegs all the way high, regardless of engine running or not, and whether or not the sender is connected.

I suspect the gauge is shorting out because all the instrument wires are in one bunch, with just enough wire from the bundle to reach to ech instrument. If a wire was shorting out, I'd expect it to affect all the instruments.

[Pcpete]

I agree with Sunbird, disconnect the sender and see if it pegs. It's much more common, in my experience, that a sender fails than a gauge.

[wgander]

I replaced the sender and it made no difference...

[wgander]

Follow Up (Sorry for the delay, I thought I did this)
Had to replace the Oil Pressure Gauge. I must have accidentally shorted it out when changing light bulbs - not a lot of space to work behind the instrument panel.

[Centerline2]

Follow Up (Sorry for the delay, I thought I did this)
Had to replace the Oil Pressure Gauge. I must have accidentally shorted it out when changing light bulbs - not a lot of space to work behind the instrument panel.

thanks for the follow up... too many times we never hear what the solution was to the problem, and so no one is able to learn from your issue.