Yanmar 3gm30 oil pressure fluctuating

[Scubaseas]

I'd check the pressure with a mechanical gauge and then look at or run an extra ground from gauge panel ground to engine block. Then from engine block to battery negative.



Most likely a faulty ground to panel or panel to battery negative circuit.

[doublebubble]

There's a lot to slowly go through, as we are permanently cruising we have had a stop for a few days and will then have a chance to investigate all the options for a remedy, unfortunately I am unable to get hold of a mechanical test guage but will go through all the above suggestions, just a question, as I do have 2 x spare oil pressure relief vallves on-board as they were here at purchase of the catamaran, lord knows why, is it a simple job? Do they just screw out and screw in, set and forget, has anybody changed one out? As I may change them as well just for curiosity sake.

[Wotname]

Originally Posted by doublebubble

There's a lot to slowly go through, as we are permanently cruising we have had a stop for a few days and will then have a chance to investigate all the options for a remedy, unfortunately I am unable to get hold of a mechanical test guage but will go through all the above suggestions, just a question, as I do have 2 x spare oil pressure relief vallves on-board as they were here at purchase of the catamaran, lord knows why, is it a simple job? Do they just screw out and screw in, set and forget, has anybody changed one out? As I may change them as well just for curiosity sake.

Fairly straightforward to replace the oil pressure relief valve. Yes, it is set and forget. There are no user serviceable parts in the valve.

The pictures from the manual tell the story the best.

Personally, I won't bother to change this valve unless it was proved to be faulty. Also, there is service manual for this engine in the library / manuals section of CF
https://www.cruisersforum.com/forums...?do=file&id=45

[doublebubble]

Thanks so much for all the input guys, very helpful, I will dive into it tomorrow as we'll be at anchor for a couple of days, hopefully we can get it sorted out and will report back if anyone's interested.

Cheers Rod.

[doublebubble]

Thanks so much for all the input guys, very helpful, I will dive into it tomorrow as we'll be at anchor for a couple of days, hopefully we can get it sorted out and will report back if anyone's interested. Just one more thing if anyone knows, does the relief valve come to a stop when screwed in, blind hole, then tension the nut or is a certain depth?

Cheers Rod.

[Wotname]

Originally Posted by doublebubble

Thanks so much for all the input guys, very helpful, I will dive into it tomorrow as we'll be at anchor for a couple of days, hopefully we can get it sorted out and will report back if anyone's interested. Just one more thing if anyone knows, does the relief valve come to a stop when screwed in, blind hole, then tension the nut or is a certain depth?

Cheers Rod.

If you look very carefully at the attachment, you will see that the relief valve screws in until the far end shoulder 'bottoms' out. Then the locknut secures it so the oil filter doesn't unscrew it.

[jimbunyard]

Originally Posted by doublebubble

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.

Originally Posted by doublebubble

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.

'Flickering' to me connotes rapid varying around a norm; if this is the case, that pretty much rules out a varying pressure problem. How large is the variation?

I'd go with the wiring diagnosis, starting with any connectors in the vicinity.

Simultaneously broken wires would be a long shot, but not impossible; the goal in modern manufacturing is repeatability, after all. I'd also check that the senders themselves are tightly screwed in, if grounding is achieved through the block.

Since gauges use such a tiny amount of signal power, the problem could also be related to a charging issue, or a connection issue elsewhere in the engine wiring, one that would perhaps seem unrelated.

[doublebubble]

Just an update, been through all the wiring, checking connections, cleaning them, tightening them, redoing ones that look dodgy, oil change and filters, the senders are earthed through the block so I can rule that out, now when on a cold start the gauges are showing great oil pressure and rock solid, as the engines warm up the both gauges start to flicker at around the same time, if I just raise the rpm from say 850rpm to 1200rpm both oil pressure readings become rock solid again, so now it seems that the only flickering, fluctuations in the gauges are at idle when the engines, oil, becomes warm.

Cheers Rod.

[Compass790]

Originally Posted by doublebubble

Just an update, been through all the wiring, checking connections, cleaning them, tightening them, redoing ones that look dodgy, oil change and filters, the senders are earthed through the block so I can rule that out, now when on a cold start the gauges are showing great oil pressure and rock solid, as the engines warm up the both gauges start to flicker at around the same time, if I just raise the rpm from say 850rpm to 1200rpm both oil pressure readings become rock solid again, so now it seems that the only flickering, fluctuations in the gauges are at idle when the engines, oil, becomes warm.

Cheers Rod.

I wouldnt worry about flickering at idle when hot as its probably just registering the pump pulses. It doesnt do it when it's cold as the oil is thick so doesnt flow through the bearings fast enough for the pressure to drop enough to show momentarily on the gauge.
As long as oil pressure is within spec all is good.

[Wotname]

Originally Posted by doublebubble

Just an update, been through all the wiring, checking connections, cleaning them, tightening them, redoing ones that look dodgy, oil change and filters, the senders are earthed through the block so I can rule that out, now when on a cold start the gauges are showing great oil pressure and rock solid, as the engines warm up the both gauges start to flicker at around the same time, if I just raise the rpm from say 850rpm to 1200rpm both oil pressure readings become rock solid again, so now it seems that the only flickering, fluctuations in the gauges are at idle when the engines, oil, becomes warm.

Cheers Rod.

I reckon you have fixed the original problem (fluctuating oil pressure around 1800 - 2000 rpm, both engines). I speculate it was poor electrical connection somewhere in the system and your efforts corrected that.

I agree with Compass790 about the flickering at low idle rpm when warm and it isn't an issue. I have seen this on older diesel engines and they still have heaps of life left in them.

[doublebubble]

Yeh I think I'll just live with it now as I know the engines are in good shape, I would just like to thank everybody for there input.

Cheers Rod.