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  #1   IP: 24.15.213.195
Old 07-29-2021, 08:53 PM
Sam Sam is offline
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Oil Pfailureressure Safety Switch

A lady friend on her 77 Oday 27 was motoring toward harbor entrance when her A4 died. She managed to restart a few times and hobble back to her slip. As usual i got the call for help and quickly noticed that when she used the starter to turn over the engine motor oil squirted out of the OPSS that was screwed in just above the oil pressure adjustment. It was easily unscrewed and a new one ordered. In the process she lost a couple of qts of oil which ended up in the bilge.

My question is has anyone ever seen an OPPS fail like this - i haven't. [Fyi - I changed her oil beginning of season and I know 4 qts were used] If so do you think an extra OPSS should become part of spare parts inventory? Thx for any input.
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Old 07-29-2021, 08:55 PM
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That's "Oil Pressure Safety Switch Failure"
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Old 07-30-2021, 12:20 AM
JOHN COOKSON JOHN COOKSON is offline
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Quote:
Originally Posted by Sam View Post
It was easily unscrewed and a new one ordered. In the process she lost a couple of qts of oil which ended up in the bilge.
How easy was it to twist the OPSS out? Maybe it was installed slightly cross threaded or the threads on the OPSS were not true and it shook loose over time.
IMO it would be a good idea for the owner to to check the OPSS for tightness and leakage for a while.

ex TRUE GRIT
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Old 07-30-2021, 12:37 PM
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It was in tight - had to take a wrench to it to free it. When I used the word "easy" meant it was not difficult procedure. Threads were were a little finer than a std bolt that I had and in good shape - no cross threading. I have never taken an OPSS apart but am guessing there is an internal "diaphram" that must have ruptured for oil to squirt out under pressure.
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Old 06-26-2022, 11:33 AM
LeewardRail LeewardRail is offline
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I know this is an old thread, but since people may have the same question in the future, I figured I would reply anyhow.


Quote:
Originally Posted by Sam View Post
My question is has anyone ever seen an OPPS fail like this - i haven't.
Quote:
Originally Posted by Sam View Post
I have never taken an OPSS apart but am guessing there is an internal "diaphram" that must have ruptured for oil to squirt out under pressure.

Yes.

Oil switches, Oil pressure sensors, CAN fail so that oil will leak out the switch itself, without leaking from the threads.

I have seen this many times while working in the automotive repair field.

But it doesn't just suddenly leak a lot of oil. They show signs of leaking before they get really bad. A periodic visual check would normally spot it.
You should do a periodic visual check of the whole engine anyhow.

(in fact, one auto mfg. had a common failure where a sensor would leak, and the liquid would then flow down the wiring loom and into a circuitboard, thereby damaging it)

Last edited by LeewardRail; 06-26-2022 at 11:37 AM.
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Old 06-26-2022, 12:23 PM
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Threads like this make me glad I have a mechanical fuel pump. No OPSS required.
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Old 06-26-2022, 01:49 PM
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Originally Posted by capnward View Post
Threads like this make me glad I have a mechanical fuel pump. No OPSS required.
No, but when they fail it isn't oil in the bilge, it is gasoline in the crankcase.
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LeewardRail (06-29-2022)
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Old 06-26-2022, 03:09 PM
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My OPSS failed last week because a wire tab broke off. Must have been 40 years old. Engine would start and then quickly stall. I found a Borg Warner Oil Switch part number S383 at a local marina that worked as a replacement. I think it would be good to carry a spare - they don't take up much room and are easily removed and replaced.
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Last edited by zellerj; 06-26-2022 at 03:11 PM.
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Old 06-28-2022, 09:13 AM
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Quote:
Originally Posted by capnward View Post
Threads like this make me glad I have a mechanical fuel pump. No OPSS required.
I am getting ready to rebuild another one to put on my 'project engine'...it has a Facet on it now that I will happily keep for fuel transfer/polishing, etc., but not installed on the motor.
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Old 06-28-2022, 11:56 AM
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I rebuilt my mechanical fuel pump about 20 years and 5000 hours ago. 5000 is an estimate because the ancient mechanical hour meter gave up the ghost recently after recording 3000 hours since the rebuild in 2000. I then discovered the new digital hour meter records hours almost twice as fast as the old one, but accurately. The old one had a small plastic worm drive to turn the numbers, and the teeth in it had started skipping before they finally broke. I did not realize until too late that I was supposed to lubricate it. Since I had relied on the old hour meter to tell me when I needed gas, at about a gallon an hour, I was surprised to fill the tank with half the amount of gas I was expecting. This means that I have many more hours on my rebuilt A4 than I thought, which is bad news, and I am due for another rebuild. It also means that I use 1/2 gallon an hour rather than one, which is good news.
I am still waiting for the failure of the mechanical pump, and the dreaded gasoline in the crankcase, often mentioned as a reason to have an electrical pump. My belief is that using non-ethanol fuel with MMO keeps the diaphragms in it from degrading.
IMHO, changing to an electric pump is not necessarily an upgrade. Just yesterday I met a guy with an A4 who had ordered a rebuild kit for the mechanical fuel pump, but in the meantime had installed an electrical pump without an OPSS. He said that the instructions on the pump were that an OPSS was optional. I told him they may be optional in a car but are required in a boat.
When I left him, he was still trying to start the engine. He said he had spark, but there was no sign of combustion. Maybe the mechanical pump was not the problem. I told him he should consult this forum.
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  #11   IP: 24.77.123.66
Old 06-29-2022, 11:10 AM
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Quote:
Originally Posted by capnward View Post
Threads like this make me glad I have a mechanical fuel pump. No OPSS required.
Good oil switches take decades to start leaking, and give plenty of warning with oil seepage before they do. The same switches are used on your road vehicle.

Keep in mind there is a reason that many fans of old cars change to electric pumps.

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Originally Posted by zellerj View Post
My OPSS failed last week because a wire tab broke off. Must have been 40 years old. Engine would start and then quickly stall. I found a Borg Warner Oil Switch part number S383 at a local marina that worked as a replacement. I think it would be good to carry a spare - they don't take up much room and are easily removed and replaced.

Yeah a spare is handy and under $10. That said, depending on where you install the oil switch, it is very easy to bypass in an emergency, or for testing.

I installed my oil pressure switch, on a T fitting where the oil pressure sensor is.

Lift out the companionway ladder and it's right there, next to the spark arrestor.

The moyer video shows installing it in a port by the transmission, but that location would be harder to inspect/service/bypass.

Last edited by LeewardRail; 06-29-2022 at 11:12 AM.
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Old 06-29-2022, 09:52 PM
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I've had an electric pump for 17 years, replaced it on principle roughly 10 years ago as an aggressive maintenance/refresh measure. There were no performance problems requiring replacement. I've had one failure of an OPSS that was my fault all the way. It was doused with antifreeze during some FWC work and did not work the next time I tried starting the engine. Other than that, zero problems.
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