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Old 30-07-2018, 14:27   #1
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oil pressure warning- theory or solved?

After reading a bunch of old posts about oil pressure warnings, I wanted to share this scenario to see if anyone can impart any more wisdom about a theory, etc;* *Our C&C 34 has a 3GM30F with a couple of thousand hrs. Engine runs like a top..change oil, filters, etc. religiously Only issue is grey smoke on hard start.. Maybe a small puff of blue, which I understand is not that uncommon. No smoke when running under load and no other issues. The other day we motored for 1.5 hrs in flat seas and as we reduced RPM's the low oil pressure alarm sounded. Killed engine and checked oil- it was ~50% so added ~1/3L qt.* Checked for oil in bilge, exhaust and water in oil and everything was fine. Restarted engine and had same issue. Decided to motor back to mooring at about 2,200 rpm. After ~30 min or so, started to hear a slight chirping from the alarm and when reduced rpm it seemed to go off at an even higher rpm (2,000 maybe?). Shut it down and sailed home for 2hrs. Started engine to get to mooring and alarm persisted, but seemed to happen at lower rpms (~1,200?). Came home, read up on the digests and figured out my troubleshooting plan. First step, replace oil pressure switch/sensor.*

Today, before replacing the sensor, I decided to start engine and do a more precise test on what rpm the alarm was sounded, but I could not recreate the issue (!?). Ran engine at 2,600 at mooring for ~15 min and no issue. Replaced the sensor anyway and everything seemed fine.*

So the question is, did I solve the problem with the new sensor or is there another theory that could explain these symptoms? I won't have time to run engine at higher rpms for an extended period for a few days, so was hoping to get a bit more educated on next steps if the issue resurfaces. Will keep the board posted on what I learn and appreciate any other insights
Thanks
WSC
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Old 30-07-2018, 14:57   #2
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Re: oil pressure warning- theory or solved?

50% of which level? Between min/max indications..?
How is the level today?

Normal engine temperature?

It should be possible to measure the function of the sensor..
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Old 30-07-2018, 15:07   #3
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Re: oil pressure warning- theory or solved?

50% full--it was half way on between min and max mark. After adding some more, it's close to the max mark. yes, normal engine temp. I'm pretty sure I don't have an oil pump issue or would think I'd see more symptoms. Trying to figure out how to add an actual oil gauge - think I need a "tee" fitting.
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Old 30-07-2018, 15:33   #4
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Re: oil pressure warning- theory or solved?

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Originally Posted by wsconner View Post

So the question is, did I solve the problem with the new sensor
My money is on that you did solve the problem. My 17 years engine has gone through both both temp and oil sensors and their gauges. My last boat also had the oil pressure sensor go and I went through the same actions as you.That's why people should know what their normal temp/press readings are.
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Old 30-07-2018, 15:58   #5
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Re: oil pressure warning- theory or solved?

I added a gauge by removing a plug into another oil galley and installing a sending unit there. I just like knowing my oil pressure, added a water temp gauge too for the same reason.
You can do a T, just be careful that your not hanging so much weight on the T that vibration can break it one day.
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Old 30-07-2018, 16:10   #6
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Re: oil pressure warning- theory or solved?

I’ve had the engine harness chafe through and cause an intermittent alarm as the sensor wire bounced and rubbed on a grounded piece of steel.

I went through the sensor troubleshooting and eventually found this by following the sensor harness from the panel all the way to the sensor.

Very annoying 😄
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Old 30-07-2018, 16:24   #7
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Re: oil pressure warning- theory or solved?

ADD A GAUGE!!!

Even a mechanical one.

How else can you know what's really going on?

Redundancy. I had the wire fall off my gauge sensor once, panicked until I noticed the idiot light was still off until I shut down the engine when it came on like it should.
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Old 30-07-2018, 18:59   #8
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Re: oil pressure warning- theory or solved?

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Originally Posted by Bill Seal View Post
ADD A GAUGE!!!

Even a mechanical one.

How else can you know what's really going on?

Redundancy. I had the wire fall off my gauge sensor once, panicked until I noticed the idiot light was still off until I shut down the engine when it came on like it should.
+1 even if it only temporary for fault finding purposes. For fault finding, you can just remove the existing low pressure sensor and fit a pressure gauge sensor (or a mechanical line and gauge). Yamnar uses BSP threads and most USA sensors will be NPT but you can fit a NPT male thread into a BSP without damage - but use some sealant. Note, you can't fit a BSP male into a NPT female.

Maybe you did have a faulty sender but it is possible you having falling oil pressure. Using a gauge is the best (and easy) way of knowing for sure.

A possible scenario from the OPs description is:

Pressure has been falling for some time but remained above the sender threshold (typically less than 10 psi for Yanmar senders)

After 1.5 hours of motoring, oil is at normal operating temperature and thus thinner than when cold. Reducing rpm causes reduced oil pump rpm resulting in an alarm.

After 2 hours of sailing, oil temperature had reduced enough to allow for enough pressure at lower rpm.

Next day, oil temperature is cold and running at dock at 2,600 rpm (loaded or not) for 15 mins is not long enough for oil to come up to normal temperature so pressure remains high enough not to trip the alarm. My tests a month or so back showed I needed to operate for about 40 mins under full load for oil temperature to stabilise.

My advice would be to use a gauge (at least temporary), failing that, use the engine loaded up (say 3000+rpm) in gear for an hour. If no alarms, it is probably OK.

FWIW, a temporary fix for low oil pressure is to use a heavier grade oil.
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Old 31-07-2018, 16:03   #9
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Re: oil pressure warning- theory or solved?

Thanks for all the replies and insights. Found a spare couple of hrs today and motored up and down coast for 60 minutes at 2,800-3,000 rpms. Slowed down every ten minutes to see if low oil pressure alarm sounded at lower rpms. All is good. I think I ran the engine hard enough to recreate the scenario from Sunday. So I'm thinking the new sender did the trick, but I ordered an real gauge and will install that just to validate.
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Old 31-07-2018, 16:38   #10
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Re: oil pressure warning- theory or solved?

Is that alarm the same for several different things?
On my old Perkins it is either low oil pressure or over hot water. Same buzzer.
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Old 31-07-2018, 16:40   #11
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Re: oil pressure warning- theory or solved?

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Is that alarm the same for several different things?
On my old Perkins it is either low oil pressure or over hot water. Same buzzer.
Same buzzer but different lights.
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Old 31-07-2018, 16:42   #12
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Re: oil pressure warning- theory or solved?

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Originally Posted by wsconner View Post
Thanks for all the replies and insights. Found a spare couple of hrs today and motored up and down coast for 60 minutes at 2,800-3,000 rpms. Slowed down every ten minutes to see if low oil pressure alarm sounded at lower rpms. All is good. I think I ran the engine hard enough to recreate the scenario from Sunday. So I'm thinking the new sender did the trick, but I ordered an real gauge and will install that just to validate.
WSC
Sounds promising and the gauge will be a bonus.
Nice to see you posting BTW,
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Old 31-07-2018, 18:44   #13
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Re: oil pressure warning- theory or solved?

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Sounds promising and the gauge will be a bonus.
Nice to see you posting BTW,
Back in the 60's through the 70's auto mfg's did away with gauges and used "idiot lights"* ,most likely at the behest from the bean counters, only to bring them back later. On boats gauges are more useful, you can't just pull over to the side of the road in case of engine failure, they provide advance warning of potential failure, unlike "idiot lights" that come on indicating, for example, low or no oil press. meaning you have SECONDS to shut down the engine , if not there's a v. good chance to ruin the engine. Of course, this is all for naught if one does not monitor the instruments.
*The term refers to the one who thought these lights were a good idea.
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Old 31-07-2018, 19:37   #14
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Re: oil pressure warning- theory or solved?

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Back in the 60's through the 70's auto mfg's did away with gauges and used "idiot lights"* ,most likely at the behest from the bean counters, only to bring them back later. On boats gauges are more useful, you can't just pull over to the side of the road in case of engine failure, they provide advance warning of potential failure, unlike "idiot lights" that come on indicating, for example, low or no oil press. meaning you have SECONDS to shut down the engine , if not there's a v. good chance to ruin the engine. Of course, this is all for naught if one does not monitor the instruments.
*The term refers to the one who thought these lights were a good idea.
Amen brother .

Apologies for the slightly off topic post but I have an engine (under restoration) that only came with a low oil pressure idiot light, nothing else. I have elected to design and fit high water temperature alarm, a water temperature gauge, an oil temperature gauge and an oil pressure gauge. Anyway that is really for another thread .
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Old 05-08-2018, 03:27   #15
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Re: oil pressure warning- theory or solved? Gauge Update

I was able to get an oil pressure gauge and install it temporarily on the 3GM30F. I definitely have oil pressure, but it was interesting to see the results. I enclosed some vid links in case anyone was interested in hearing/seeing these results. At 2500 rpm immediately after start up the pressure bounced between 40-50 psi. https://youtu.be/Ym6CBjTXG0Q.

At 3000 rpms after 15 min run time, the pressure held steady at 62 psi. https://youtu.be/vy_7_X626Yo

When backing down throttle to `800 rpm the pressure bounced around at 20 psi. https://youtu.be/PPxDKUXHUL8

According to the yanmar service manual, pressure at idle should be 7.2 psi and at 3,500 rpm should be 42-57 psi. . Not sure what the results actually mean, but I at least know there is pressure and have some form of baseline measurements to assess.
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