Anatonomy of an Oil Pressure Sender

[mcandmar]

Another one for the curious minds out there. This is the old style unit with a round outer casing from a 1991 7A car. I finally got around to replacing this unit as it went faulty, whenever the engine had fully warmed up the sensor failed to register anything below 1.5bar. I just couldn't take it any longer with the autocheck beeping away while sitting in traffic.

Fairly simple device, there is a small plunger in the bottom of the unit that the oil pressure pushes against raising the platform. On the front side shown there is a resistance track for the gauge, and on the back side there is a contact for the low oil pressure warning.

The sender seem to require voltage and the pressure gauge logic to work, so with an AUX gauge cluster wired up and reading 13.5volts, the wire to the sender was giving out a little over 8 volts. Seems a bit of an odd figure to me

[mcandmar]

For future reference, the connections are Black/White to terminal G for the Pressure Gauge. Blue/Black to terminal WK for the Autocheck Low oil pressure Warning.

Later ABY style sender shown in pic..

[Error404]

Interesting Mark, I guess the track gets worn as per the fuel gauge sender and starts to get lazy / useless... mine is on the way out, i have had to disconnect the low pressure warning as you know, and pressure readings appear low although i'm yet to properly test the oil pressure with a proper gauge
don't suppose you managed to find any VDO part number on the sender did you?

[mcandmar]

On the oil pressure, over the last six years i've watched the CQ drop from over 2bar at warm idle down to 1.5bar, and then the gauge went faulty. Now with a second hand ABY sensor i havent seen it drop below 2bar. So who knows what the actual pressure is, keeping in mind this bottom end has clocked up over 300k miles i would expect it to be low.

I'll check for a part number though its so old and rusty and doubt i will be able to read it. I'll check the new sensor on the ABY block too...

[Jeffer]

interesting write-up!

[Error404]

nice one Mark.
I've bought a decent quality 100psi industrial gauge and some fittings to make up a pressure test kit to see what pressure I'm actually running, my gauge never reads above 3.5bar and drops to 1bar at warm idle, pretty sure my tappets would be screaming if that was actually the case.

[mcandmar]

Not seeing anything like a part number, all that is on the old sensor is "621 1G 0-5 BAR 0,60 ITALY". New sensor only has VDO and the two terminals stamped into the casing.