Another Low Oil Pressure Query

[Compass790]

Originally Posted by a64pilot

In my opinion it’s controversial but Melling says worn rod bearings can cause an increase in oil pressure at idle. Melling is a very good source, they are not a fly by night or new Company.
https://www.melling.com/aftermarket-...u-k/technical/

Pressure vs flow paragraph.

I say it’s controversial because it’s not been my experience, but then I probably have never seen just rod bearing wear? What I have seen is low oil pressure across the board when hot, Especially at idle, and that dreaded hollow knock.
I misdiagnosed one as a kid based on the knock, but the knock turned out to be an automatic transmission flex plate cracked.

I've had an experience with not just rod bearing wear, main bearings also worn but rod bearing was completely gone & the oil pressure still rose when it was revved.
Not saying it can't happen but I'd very much doubt it would be to the extent the OP has.

[wingssail]

Originally Posted by a64pilot

Possibility of sludge is why I asked what his oil change interval was.... one thing that could is sludge again, if the screen is partially plugged at higher flow rates the screen blockage blocks the oil flow and pressure will drop just because the pump can’t get enough oil. Reduce RPM and therefore flow and the blockage isn’t great enough to cause a loss in pressure, so it rises....
Sludge could also restrict oil passages to the head....Now, this is all theory but the weird oil pressure rising at lower RPM could be explained by a blockage in the oil pick up screen

Thanks for the comments.

We're back in port again after a great sail today (20 miles upwind then a finish downwind in 20 knots, a bit dicey on getting the genoa off but we did it).

As to the comments about oil change intervals ands sludge build up.

I have to say we've seen no indication of any sludge build up. The pan was off two months ago and everything was clean, pan, crank, oil pick up, anything we could see. The valve cover was off a year ago, also clean. And even now, when I eyeball inside with the the oil filler cap on the valve cover off, there is nothing black. So I think the engine is clean. of course that says nothing about what is inside the oil passages, maybe we will find out.

As for our oil change intervals; unfortunately my logbook does not include these (it will in the future, my bad). But while we don't have a regular interval, we change periodically, usually before any passage.

Now that we can work on the engine without worry about not being able to run it (we have shore power) we'll proceed as several people have suggested.

Thanks for the ideas, we'll keep you all posted.

[BruceS]

I think the reference to oil pressure dropping when revving in my case was more to do with if it was under no load or under a lot of load.
I'm guessing the original post was comparing at idle with no load (out of gear?) or under load. (especially if it was over propped or close to it?)
Love to hear the diagnosis when found out.

[Kastaway]

My guess like others would be PRV spring issue. You already know this but I’ll say it anyway (I’ve been drinking). At a set temperature the bearing clearances don’t change that much with RPM. What dose change a lot with increasing RPM is the output of a fixed displacement pump. Just like you wouldn’t expect to see higher exhaust gas flow out of your engine at idle compared with say 2000 RPM. If you’re feeding the pump all it can drink spinning it quicker will output a higher flow with an equally proportional increasing resistance to the flow (pressure). I don’t know your engine but I suspect all this high pressure oil leaves the pump and rushes along a gallery to some sort of pressure control device to meter it to the whirly parts of the engine in some controlled fashion (or not). It then probably passes by the pressure gauge (sender) on the way to the whirly bits. If it’s not finding it’s way to the top of the engine and if you’re correctly measuring that there’s less of it when you increase the revs then it sounds like you dumping it back into the pan. I’ll be watching so you can call me a name when you discover that it’s something completely unrelated.

[wingssail]

Originally Posted by Kastaway

My guess like others would be PRV spring issue. You already know this but I’ll say it anyway (I’ve been drinking). At a set temperature the bearing clearances don’t change that much with RPM. What dose change a lot with increasing RPM is the output of a fixed displacement pump. Just like you wouldn’t expect to see higher exhaust gas flow out of your engine at idle compared with say 2000 RPM. If you’re feeding the pump all it can drink spinning it quicker will output a higher flow with an equally proportional increasing resistance to the flow (pressure). I don’t know your engine but I suspect all this high pressure oil leaves the pump and rushes along a gallery to some sort of pressure control device to meter it to the whirly parts of the engine in some controlled fashion (or not). It then probably passes by the pressure gauge (sender) on the way to the whirly bits. If it’s not finding it’s way to the top of the engine and if you’re correctly measuring that there’s less of it when you increase the revs then it sounds like you dumping it back into the pan. I’ll be watching so you can call me a name when you discover that it’s something completely unrelated.

Don't worry, I won't call you a name for concluding that the pressure regulating valve is dumping oil and reducing the pressure. Several posters have concluded that, and it's my conclusion and hope too. However, we are just now getting into it and time will tell. In the end, if an overhaul is in the card, so be it. No name calling or recriminations.

Thanks for the input.

[Scubaseas]

Worn or clogged cam bearings would account for all your symptoms including reduced oil to rockers. At the hours you have it might be worth while pulling the oil pump and possibly the cam along with putting some plastigauge on the rod and main bearings. Also quite possible the problem is one of the o-rings between the block and gear plate.

You need pressure and volume. The only place you loose both is through excess clearance someplace.
Me? I'd pull it to find out if shimming the regulator doesn't solve both the pressure and upper lube issues. But that's just me pushing a wrench for over 55 years

[CassidyNZ]

Originally Posted by Scubaseas

Worn or clogged cam bearings would account for all your symptoms including reduced oil to rockers. At the hours you have it might be worth while pulling the oil pump and possibly the cam along with putting some plastigauge on the rod and main bearings. Also quite possible the problem is one of the o-rings between the block and gear plate.

Actually I’m not sure I agree with the camshaft diagnosis. Having had quite a major issue with a frost plug at the back of the camshaft where all the oil got pumped out of the engine in very short order (there is a post on this board detailing the event), even with oil pouring out of the back of the engine, specifically from the rearmost cam journal, the oil pressure buzzer never went off until all the oil was gone.

The schematic below is for a 4JH2E Yanmar. Maybe the 3JH is different but probably not. There are two pressure regulator valves, the sender unit sits between them. So if either valve dumps pressure, the sender will immediately sense this and set off alarms. Oil supply to the top of the engine is after all the bearings (crank and cam).

If any of the bearings were causing a loss of pressure to the extent that the rockers never got any oil, surely the bearings would by now be audibly complaining?

I’d bet money on a faulty relief valve.

[Scubaseas]

CassidyNZ: It's a 3JH2E per the OP which I show as a gear type oil pump with a single relief valve in the filter housing. There is no turbo on it. If it did or didn't it still should have good oil flow to the rockers. there might be a regulator valve in the pump itself but I doubt it. If there is there are no parts available for it.



I had said "I'd pull it to find out IF shimming the regulator doesn't solve both the pressure and upper lube issues." (my caps)


Loosing the oil due to a rusty plug is not the same as low flow and pressure drop due to excessive clearance between shaft and bearing being too much. Different beast all together.



I have seen worn bearings without even a hint of knocking. I would suggest the low flow to the rockers and the low oil pressure are related. As in too much clearance somewhere. Worn mains, idler or cam bearings would all account for the lack of flow and loss of pressure at the same time.

[wingssail]

Originally Posted by Scubaseas

CassidyNZ: It's a 3JH2E per the OP which I show as a gear type oil pump with a single relief valve in the filter housing. There is no turbo on it. If it did or didn't it still should have good oil flow to the rockers. there might be a regulator valve in the pump itself but I doubt it. If there is there are no parts available for it.

I had said "I'd pull it to find out IF shimming the regulator doesn't solve both the pressure and upper lube issues." (my caps)

Loosing the oil due to a rusty plug is not the same as low flow and pressure drop due to excessive clearance between shaft and bearing being too much. Different beast all together.

I have seen worn bearings without even a hint of knocking. I would suggest the low flow to the rockers and the low oil pressure are related. As in too much clearance somewhere. Worn mains, idler or cam bearings would all account for the lack of flow and loss of pressure at the same time.

"there might be a regulator valve in the pump itself but I doubt it. If there is there are no parts available for it" There is a regulator valve in the oil pump according to my 3JH2 manual but it is not removable or serviceable and only comes as a unit with the pump.

Today I collected the necessary parts and tomorrow I will do

Step 1: Replace the oil pressure switch for the buzzer and also install a mechanical oil pressure gauge (BTW, both switch and pressure sensor are mounted on the right hand side looking from the flywheel, on an outlet from the oil galley.) The fitting on the oil filter casing is blocked with a plug and shown that way in the manual.

Step2: (assuming that step 1 does not make symptoms disappear) I will remove and inspect the oil pressure regulator which is in the lower part of the oil filter casing and likely buy a new one if re-shimming does not cure the problem, or even if it does.

Step 3: Needed if step 1 & 2 do not solve the problem. Pull the engine and disassemble and replace whatever bearing surfaces there are, and whatever else we need to do. Not looking forward to this one.

[BruceS]

[QUOTE]
In 27 years we've put 6658 hours on this engine.
[ENDQUOTE]


Maybe work backwards from 3?

[wingssail]

[QUOTE=BruceS;3159394]

In 27 years we've put 6658 hours on this engine.
[ENDQUOTE]


Maybe work backwards from 3?

From what I've heard these engines can go quite a bit longer. Other than this problem and six months ago a leaking rear main seal, we see nothing to indicate that the engine is worn out. No smoking, noise, hard starting, loss of power, drips, Nothing.

But maybe we're wrong. Maybe it's time. I hope not.

I'm going to start with the simple steps and work up the ladder as several people have suggested.

[Scubaseas]

Hopefully 1 & 2 solves your issues. Might be an idea to cut open and inspect the filter or even better send an oil sample out for analysis. A clean filter and no or little metals in the oil test would be good proof of no other issues if the pressure and flow to rockers are corrected by the secondary regulator valve. Best wishes.

[Scubaseas]

There is a regulator valve in the oil pump according to my 3JH2 manual but it is not removable or serviceable and only comes as a unit with the pump.

So the good news is that with a dual regulator system, typically the second one, in your case in the filter housing is typically there to reduce the pressure to the oil cooler and or turbo. Also good news is that also makes it more likely to be your problem if the piston is getting stuck open. Pull out the piston that's under the spring and see if it's worn more on one side than the other. If so it's probably getting stuck /cocking itself in the bore.

[jimbunyard]

That the problem manifested itself rather abruptly doesn't really support the excessive-wear hypothesis.

Though the engine has 6500 hours on it, the majority of them are at very low load; according to the power curve, at 2000 rpm there is about 19 hp available at the flywheel, 55A X 14 vdc = 770 watt = 1 hp@ 20% efficiency = < 5hp load of 19 available. With even reasonably diligent previous maintanence the bearings should be fine.

Makes no sense at all to assume things are bad, especially given the ease with which various checks can be made to determine what the problem actually is. The plan laid out by Wings is good.

Don't think it's been suggested, and it would scare some, maybe most, but you could run the engine at less than 2000 rpm at no load with up to 75% diesel in the crankcase for about half an hour to clean out any sludge and blockages.

Wouldn't normally do it before checking the filter-mounted regulator valve though, since its operation seems suspect.

Though the pump mounted 'regulator' valve is listed as such in the manual, it is really a relief valve; only opening in overpressure situations, whereas the regulator valve in the filter housing maintains the pressure between set parameters.

The relief valve could be the problem, but since the system seems to be building pressure more or less normally and consistently, the chances are that it isn't the source of the problem.

Of course the problem could be a concatenation of issues, but the idea of checking, cleaning and perhaps shimming the pressure regulating valve is the logical first step.

[kmacdonald]

What is bothering me about the rear main oil seal being replaced is why it started leaking. Is the rear main bearing worn?