High Oil Pressure- Yanmar 6LYA-STP

[BMUR21]

I have a Yanmar 6LYA-STP in my Mainship 34 RR with about 3000 hour in the engine, new to me as of last year. I did an oil change in the spring and started experiencing high oil pressure readings. The correct oil, filter, and amount of oil in the engine are correct and I used a mechanical gauge to verify the PSI was correct on the helm gauge.

I talked to a number of diesel guys and the Yanmar folks in my area and they all said the pressure relief valve needs to be replaced. I had that work performed by the Yanmar shop (air cooler had to come off so that was Sonic cleaned) and a new pressure relief valve installed. We cranked her over and the engine was still running high.
At operational temp:
Idle- 50 PSI
In gear up to 1600 RPM- 60-65 PSI
2000 RPM- 75 PSI
2400-WOT (3100)- 78 PSI

Yanmar shop tells me that it’s the oil pump and has to pull the engine to drop the pan to access it and I am feeling like that is pretty extreme after the issue started with an oil change. On top of that if the engine comes out you might as well… that list is a long one.

Exhaust and engine temps are normal and I don’t have anything that is leaking oil. I flushed and have changed the oil out (I get the differing opinions on the flush) but am wondering if anyone has either experienced this or has some other areas to look at before I go with the Yanmar shop’s recommendation.

Thanks,
BMur

 

[kchace]

I dont know how an oil pump can manufacture higher oil pressure than normal. It’s basically 2 gears. The oil pressure is regulated from going too high by a relief valve. If that’s been changed and you’ve verified with a mechanical gauge that the readings are accurate, the next thing I would do is change everything that you changed just before the oil pressure started running high. Meaning, I would change the oil and filter again. Use exactly the type and quantity of oil specified in the manual and use a genuine Yanmar filter.

Ken

 

[DavidM]

From my experience with two Yanmar 6LYs, 50 psi at idle and 78 psi at high rpm’s may be a little high but only by 10 psi. You changed the relief valve and as kchace notes oil pumps do not all of a sudden make more pressure.

But make very sure the oil spec is right. Straight 40 wt can cause what you are seeing.

Otherwise fugetaboutit.

David

 

[AquaAura]

I would change the oil and filter again before anything else. Overtime low oil pressure is bad but a little high I wouldn't worry and especially wouldn't start pulling the motor apart without first doing another oil change. Did you do the oil change and if not maybe the wrong viscosity was used causing higher pressure.

 

[twistedtree]

Did the pressure increase happen immediately after changing the oil and filter? If so, that is almost certainly the source of the problem. What oil weight did you use? Did you use a Yanmar filter, or from some other source? Have you changed the oil and filter again since the high pressure started?


One common issues is that the rubber seal for the oil filter sticks in the filter housing rather than coming off with the filter. Then when you install the new filter you end up with stacked seals. Perhaps something like that is preventing proper flow through the filter.


I agree with others that it's not the oil pump, and the fact that the dealer is suggesting it casts great doubt on their capabilities. Pressure will decrease as a pump wears, not increase.

 

[Jeff F]

On top of that if the engine comes out you might as well… that list is a long one.

I have nothing constructive to add, but recently ran across a sister ship with a brand new QSB7. Owner reported it quiet, smooth and expensive.

Sent from my moto g play (2021) using Trawler Forum mobile app

 

[STB]

First, check your oil pressure reading. And check it again with a different mechanical gauge. And, do this even if you already have with a different different gauge. One doesn't want to hunt a non-problem.

So, looking at your service manual...
-- https://scyr.org/stellablue/images/stories/pdfs/6LY2-STE_206LY2A-STP_206LYA-STP-HINSHI-H8-011-1.pdf

It looks like your oil pump is designed to, nominally, produce /up to/ 114psi, which is then regulated down to 43psi by the pressure relief valve. (Page 5-3)

So, it is not a failure for the pump to be able to produce a much higher than operational psi. It is the design. And, as others have said, oil pumps don't suddenly make more pressure, anyway. So, I can't imagine that it is the oil pump.

So, the oil pressure isn't being regulated down enough by the oil pressure relief valve. So, what could cause that? Either the lubricating oil is too viscous, or the relief valve is bad, or there is a constriction somewhere such that relieving the amount of pressure that is building is beyond the design limit of the valve.

Looking at the oil flow in your system (See page 5-2), other than a significant galley constriction, it looks like a constriction associated with the filter or cooler could be the problem. This includes not only the filter and cooler, but also the associated plumbing.

It looks like, in theory, it could also be a constriction associated with the turbo, including the plumbing to the turbo, if you have one but I've never seen that cause the problem, so I'd back burner that one unless other options don't pan out. Normally the turbo will tell you that it is starving well before the oil pressure gauge.

So, given that the oil and filter were just changed, those are my first suspects. I'd change them again. And, in the process, I'd be careful to use the correct oil. And, I'd be careful to check in and around the filter housing for an errant seal/gasket/o-ring, label, plastic bag bit, etc. If I didn't find anything, I'd pull the hoses and check there. Might as well do it once.

If that didn't fix the problem, I'd check the oil cooler. It could be clogged on some debris, perhaps that got pushed in from the filter or filter plumbing, as it is downstream from the filter. Again, I'd go ahead and remove and check the hoses, etc. Do it once. Answer the question.

If that still didn't fix the problem, I'd turn to the pressure relief valve. It is possible that it was replaced with a bad one. Even new parts can be bad.

Next, I would turn my attention to the turbo if you have one. Make sure it seems healthy. I'd check this sooner if it is offering ay signs of distress.

Finally, it is possible to shim the oil pressure relief valve to adjust it (See 5-7). But, unless you've messed with the shims, or disassembled the valve for some reason, this really should be set at the factory.

Before I'd start adjusting that oil pressure relief valve, I'd make sure that I had disassembled everything related to the filter and cooler and was running the correct oil.
And, I'd get someone else to check me on that.

More than likely, I'd bet there is a constriction related to the filter from the filter change. And, if it isn't there, I'd bet there is one downstream of the oil filter where something got pushed toward, into, or beyond the oil cooler.

Occum's Razor tells me that you changed the filter and the fluid and these things are the simplest, most direct causes of this problem, so one of these things is the cause of the problem.

Just my thinking....

 

[BMUR21]

Thanks all for some of the feedback and all the comments are in line with what I have been thinking and discussing.

I have changed the oil a few times and the proper oil is in the engine with a Yanmar genuine filter. I do think I might have a constriction as STB mentioned and I also have put some thought into the turbo as a source. I am going to keep investigating but also listen to DavidM and “fugetaboutit” and run the boat.

I’ll let you know if I find the trouble spot or is it corrects itself with another oil change.

 

[helm]

The numbers you posted are pretty much where my pair of yanmar 6lya-STE engines run, just FYI
Eric

 

[STB]

My big questions here are these:

1) How confident are we that this changed all at once proximal to the oil change?, and
2) Do you still have the original oil, before that oil change?

If we think this always was or likely creeped up over time, I'd be okay changing the oil and using it while I sorted it or made peace with it. But if something suddenly changed, I'd be concerned about that constriction. It is likely a real problem and something is unlikely to be getting the lubrication it expects.

There is another possibility: The old oil was wrong or bad. For example, maybe it was majorly diluted with diesel?

If you've still got the old oil, I'd send off a sample to a lab. It only costs ~$25:

-- https://www.amazon.com/WIX-Filters-24077-Analysis-Pack/dp/B000CSEUQ0

You might find that you have an injector injector pump or lifter pump or whatever related dilution issue and that what you are seeing is normal for the engine and what you had before, even if closer to the book, was actually from bad oil. If that's the case, an easy fix could save you a lot of engine life over time.


From the peanut gallery....

 

[Swinkles]

I have a Yanmar 6LYA-STP in my Mainship 34 RR with about 3000 hour in the engine, new to me as of last year. I did an oil change in the spring and started experiencing high oil pressure readings. The correct oil, filter, and amount of oil in the engine are correct and I used a mechanical gauge to verify the PSI was correct on the helm gauge.

I talked to a number of diesel guys and the Yanmar folks in my area and they all said the pressure relief valve needs to be replaced. I had that work performed by the Yanmar shop (air cooler had to come off so that was Sonic cleaned) and a new pressure relief valve installed. We cranked her over and the engine was still running high.
At operational temp:
Idle- 50 PSI
In gear up to 1600 RPM- 60-65 PSI
2000 RPM- 75 PSI
2400-WOT (3100)- 78 PSI

Yanmar shop tells me that it’s the oil pump and has to pull the engine to drop the pan to access it and I am feeling like that is pretty extreme after the issue started with an oil change. On top of that if the engine comes out you might as well… that list is a long one.

Exhaust and engine temps are normal and I don’t have anything that is leaking oil. I flushed and have changed the oil out (I get the differing opinions on the flush) but am wondering if anyone has either experienced this or has some other areas to look at before I go with the Yanmar shop’s recommendation.

Thanks,
BMur

Dear sir,
I have a 43 main pilot with twin Yanmar 440 same as yours. I’m having the same oil pressure problem. Could you reach out and tell me what you found on yours? Rjswink@gmail.com
Thanks Swinkles

 

[Lepke]

That's not high oil pressure. If oil isn't getting past the seals I wouldn't worry. If anything bearing surfaces are better off.

 

[BruceK]

I have a Yanmar 6LYA-STP in my Mainship 34 RR with about 3000 hour in the engine, new to me as of last year. I did an oil change in the spring and started experiencing high oil pressure readings. The correct oil, filter, and amount of oil in the engine are correct and I used a mechanical gauge to verify the PSI was correct on the helm gauge...


Thanks,
BMur

Accepting the change immediately follows the oil and filter change, and if (as it sounds) this is the first oil change post purchase, the oil drained may have been of lower viscosity for some reason than what replaced it, which is presumably the correct grade. Worn engines may be dosed with oil thickeners or high viscosity oil to disguise wear but this seems the reverse of that.
It`s possible what you are seeing, after the oil change, is the norm for that engine with the correct grade oil. Posts above don`t suggest the psi, although higher than usual, is excessively high.