Oil Pressure Sender failure modes?

[nola mike]

TL;DR:
What would cause an oil pressure sender to fluctuate between reading correctly and reading zero?

Been chasing an oil pressure gauge/issue all summer. Mercruiser, standard analog sender/gauge. It will run fine for long stretches of time, steady at 60 psi, then drop to "zero" (actually more like 5-10, which is where the gauge reads engine off). Anywhere from a second or 2 to much longer. Goes very quickly between readings, so seemed electrical. Ran it at 3500 rpm reading zero for 10 miles a few days ago, so pretty sure at this point that it's not actually low pressure. No pattern on what triggered it or cured it, but becoming more common. Gauge checks out, all connections are squeaky clean, nothing else at the helm malfunctions when the pressure drops. Bench testing the sender checked out (I didn't have anything handy to pressurize it but readings fluctuated a bit when I blew into it). Finally swapped out the sender with a spare. So far so good, but we'll see. My concern was an intermittent clog/air leak at the pickup. Question is do senders fail in that pattern? If so, is it typically an electrical problem or something obstructing the sender hole? Doesn't really matter, just curious.

 

[DeepCMark58A]

Put a pressure gauge where the sensor is, rig up a t with pipe fittings. See what is really happening.

 

[nola mike]

Put a pressure gauge where the sensor is, rig up a t with pipe fittings. See what is really happening.

Intermittent failure in a difficult location. Not really possible to T in there. Like I said, if this was a real pressure then I wouldn't have been able to take the kids skiing this am lol.

 

[Chris1956]

Gee, oil pressure sensors on MerCruisers often fail. The one on my '88 was a can-type. it looked the same as the automotive one on autos of that time.

Ohm out the wiring, clean the connectors and if that doesn't get it, replace it.

 

[Pmt133]

Mine uses a VDO type sender... stays at 45 all the time lol. They are notorious for failing.

 

[nola mike]

Gee, oil pressure sensors on MerCruisers often fail. The one on my '88 was a can-type. it looked the same as the automotive one on autos of that time.

Ohm out the wiring, clean the connectors and if that doesn't get it, replace it.

Yeah, I already did (with a 40 year old spare that I had), and it is an auto can type. I'm just curious as to how they fail moreso than how to troubleshoot the system. Of course intermittent electrical issues are tough.

 

[Grub54891]

Clean all th connections including the large bullet connection at the engine, and under the dash. Also you can do a jiggle test when it’s not working and see if it comes back to life for a bit. That will narrow down where the issue is.

 

[nola mike]

Clean all th connections including the large bullet connection at the engine, and under the dash. Also you can do a jiggle test when it’s not working and see if it comes back to life for a bit. That will narrow down where the issue is.

Already did all that, no changes. Have put about 50 miles on the "new" sender including some good chop with no recurrence so far...

 

[StewartL]

Yep, senders can fail exactly like that usually electrical, not mechanical. Internal resistance gets flaky, causing the gauge to bounce or drop out. Since your gauge and wiring check out and the new sender seems to fix it, that’s likely the culprit. A clogged pickup or air leak would show slower, more consistent pressure drops, not instant zero. Senders just wear out over time, especially with heat and vibration. If the problem comes back, double-check the ground, but odds are the old sender was just dying.

 

[Scott06]

TL;DR:
What would cause an oil pressure sender to fluctuate between reading correctly and reading zero?

Been chasing an oil pressure gauge/issue all summer. Mercruiser, standard analog sender/gauge. It will run fine for long stretches of time, steady at 60 psi, then drop to "zero" (actually more like 5-10, which is where the gauge reads engine off). Anywhere from a second or 2 to much longer. Goes very quickly between readings, so seemed electrical. Ran it at 3500 rpm reading zero for 10 miles a few days ago, so pretty sure at this point that it's not actually low pressure. No pattern on what triggered it or cured it, but becoming more common. Gauge checks out, all connections are squeaky clean, nothing else at the helm malfunctions when the pressure drops. Bench testing the sender checked out (I didn't have anything handy to pressurize it but readings fluctuated a bit when I blew into it). Finally swapped out the sender with a spare. So far so good, but we'll see. My concern was an intermittent clog/air leak at the pickup. Question is do senders fail in that pattern? If so, is it typically an electrical problem or something obstructing the sender hole? Doesn't really matter, just curious.

I would suspect you have a ground issue between gauge and the block maybe at cannon plug. Not sure if power supply to gauge or voltage drop to gauge will do it...

as mentioned put a mechanical gauge on a T run it so you know there is oil pressure in the engine.

 

[nola mike]

I would suspect you have a ground issue between gauge and the block maybe at cannon plug. Not sure if power supply to gauge or voltage drop to gauge will do it...

as mentioned put a mechanical gauge on a T run it so you know there is oil pressure in the engine.

Nope. ALL connections everywhere were redone when the engine was out this spring. Cannon plug was disconnected and cleaned (again... done in the spring). None of the other gauges are acting strangely (same 12v supply). As mentioned, not really possible to t into my sender the way things are set up. it would have to be a total loss of power to have it drop to zero. I'm going to cut open the old sender and see what it looks like. A couple of hours of skiing this am with no wonkiness still.