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Old 08-10-2020, 23:54   #1
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Yanmar 3gm30 oil pressure fluctuating

I have a question just in case anyone else has experienced this, we have 2 x yanmar 3gm30's in our cat, with the engines at 1600rpm both oil pressure gauges are reading well and steady, at 2000rpm both gauges start flickering quite badly, the oil pressure lights do not blink, engines are regularly serviced and use genuine yanmar filters, both oil pressure relief value balls and springs have been replaced with no noticeable changes, checked wiring and cleaned connections, could it be that both oil pressure senders are faulty, don't wanna purchase two senders and have the same issues, if anyone has any clues I'm all ears, e.g. neither engine use any lube oil and run just fine.

Cheers Rod.
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Old 09-10-2020, 00:28   #2
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Re: Yanmar 3gm30 oil pressure fluctuating

Is there any addition engine vibration around 2000 rpm?
How long has this been occurring?
Have the engine mounts been changed recently?
What happens at higher rpm, say 2,500 and 3,000 rom?
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Old 09-10-2020, 00:32   #3
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Re: Yanmar 3gm30 oil pressure fluctuating

If they are both doing it it's more likely an electrical supply problem.
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Old 09-10-2020, 01:38   #4
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Re: Yanmar 3gm30 oil pressure fluctuating

There is an engine vibration at around 2000rpm, no the Engine mounts have not been changed, at around 2500 to 3000 rpm the vibration starts to diminish, an electrical issue was the next area, the port engine doesn't fluctuate as much as the stb, so an electrical issue sounds feasible but it just seems a bit weird that the same problem stb to port have an electrical oil pressure electrical issue, as there perfectly stable at 1600 to 1800rpm.
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Old 09-10-2020, 01:42   #5
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Re: Yanmar 3gm30 oil pressure fluctuating

Do the oil pressure fluctuations also decrease when the engine vibrations dimmish as you approach 3,000 rpm?
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Old 09-10-2020, 01:43   #6
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Re: Yanmar 3gm30 oil pressure fluctuating

Does each engine have it's own starting battery and engine panel supply?
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Old 09-10-2020, 01:51   #7
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Re: Yanmar 3gm30 oil pressure fluctuating

Thanks for the reply, both engines have own separate start batteries/ panels, I may have seen the pressure's stabilise (I think ) I'll have to revisit that bit but I don't think so.
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Old 09-10-2020, 02:31   #8
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Re: Yanmar 3gm30 oil pressure fluctuating

From what you have posted, I am thinking it is vibration problem, either in the connector or harness or in the sender itself.

But don't buy two senders, just get one and try it in each engine.
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Old 09-10-2020, 08:21   #9
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Re: Yanmar 3gm30 oil pressure fluctuating

Put a mechanical pressure gauge on it to verify pressure readings. Sounds more like an electrical/ground issue if they are both doing is at the same time. Sending units are the most common fault however.
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Old 09-10-2020, 10:36   #10
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Re: Yanmar 3gm30 oil pressure fluctuating

Quote:
Originally Posted by RaymondR View Post
If they are both doing it it's more likely an electrical supply problem.
Check the grounding.
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Old 09-10-2020, 12:14   #11
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Re: Yanmar 3gm30 oil pressure fluctuating

Oil pressure senders are grounding units. I would look at all the connections, the gauges, and entire wiring harness.
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Old 09-10-2020, 13:07   #12
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Re: Yanmar 3gm30 oil pressure fluctuating

It will be interesting to hear the cause. I think it is not a sender problem because you are seeing both doing the same thing at the same RPM. I have a hunch that it is a harmonic pulse generated by the pumps from these two identical engines. One way to rid harmonics from fluid lines is to tee in a damping bulb before the sensors. Many houses have similar bulbs in the water lines to dampen water hammer, that’s the loud slam sometimes heard if a water valve is suddenly shut in the system. These bulbs contain an air bubble. They are mounted with the only fitting vertically down and the bulb up trapping an air bubble and allowing pressure waves to dampen in the pillow of air you trapped in the bulb. It will not bleed pressure or cause the motor to lose oil pressure. The air will also pressurize to the pump output pressure and stabilize.

If you test with a mechanical gauge, tee in at the sender pressure fitting. Then run the engine. If it’s the sender, the gauge shouldn’t fluctuate much, if at all. If it’s the pump, gauge fluctuation will be evident along with the sender signal fluctuation.
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Old 09-10-2020, 16:06   #13
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Re: Yanmar 3gm30 oil pressure fluctuating

Have you looked at the earth on the gauges themselves even the smallest vibrations can travel to a wire that is broken or corroded and will give you a faulty reading.
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Old 09-10-2020, 16:11   #14
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Re: Yanmar 3gm30 oil pressure fluctuating

Quote:
Originally Posted by doublebubble View Post
Thanks for the reply, both engines have own separate start batteries/ panels, I may have seen the pressure's stabilise (I think ) I'll have to revisit that bit but I don't think so.
Is there any common ground connection between the 'seperate' battery and panel of each engine?

Said another way - are the electrical systems on each engine truly seperate with no common point anywhere?
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Old 09-10-2020, 16:18   #15
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Re: Yanmar 3gm30 oil pressure fluctuating

Quote:
Originally Posted by chasmains View Post
It will be interesting to hear the cause. I think it is not a sender problem because you are seeing both doing the same thing at the same RPM. I have a hunch that it is a harmonic pulse generated by the pumps from these two identical engines. One way to rid harmonics from fluid lines is to tee in a damping bulb before the sensors. Many houses have similar bulbs in the water lines to dampen water hammer, thatís the loud slam sometimes heard if a water valve is suddenly shut in the system. These bulbs contain an air bubble. They are mounted with the only fitting vertically down and the bulb up trapping an air bubble and allowing pressure waves to dampen in the pillow of air you trapped in the bulb. It will not bleed pressure or cause the motor to lose oil pressure. The air will also pressurize to the pump output pressure and stabilize.

If you test with a mechanical gauge, tee in at the sender pressure fitting. Then run the engine. If itís the sender, the gauge shouldnít fluctuate much, if at all. If itís the pump, gauge fluctuation will be evident along with the sender signal fluctuation.
Interesting hunch however if it was so, surely this will have been reported before by other owners of the tens of thousands of identical 3GM30 engines.

I do agree it is an interesting fault and one I hope the OP will track down eventually.

There is a lot to be said for mechanical gauges in this instance!
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