Low oil pressure at idle only Yanmar 4JHE

[cgebluewater]

I recently installed a Yanmar oil pressure sending unit and gauge on a 1986 Yanmar 4JHE. When the engine is cold the reading is at 4 bar which is 12 o'clock straight up at idle and at all rpm ranges. after the engine runs long enough to get the oil temp up to operating temp the oil pressure maintains 4 bar until rpm drops to about 2000 rpm, about 3 bar at 1800 rpm, about 2 bar at 1500 rpm, and about 1 bar at about 1200-1300 rpm which does not bother me to much. But what concerns me is that the gauge is just hardly above zero at idle of 750 rpm. Is that enough oil pressure at idle ?

The low oil pressure alarm is operable but does not alarm at idle. it does alarm when the engine is stopped with key on or before startup with key on as it should.
I changed the oil and oil filter to make sure the oil was not thinned for any reason. the oil pressure readings where exactly the same after the oil and filter change using Shell Rotella triple protection multi-viscosity 15-40

[cgebluewater]

Any owners with an older Yanmar that can give any insight on the oil pressure reading at idle ?

[Reefmagnet]

Firstly, there's probably no guarantee the gauge is accurate - the "idiot light" is probably better to trust for total oil pressure loss. Be that as it may, low oil pressure at low rpm at operating temps is most associated with wear in either the oil pump or main bearings. There's no shortage of high hour engines that have the same issue. Can't speak specifically for Yanmars, but my old car has had the same issue for the 8 years I've owned it and is still running strong.

[a64pilot]

Mine reads about 10 or 12 PSI at idle, hot. Idle is 750 RPM or so. Of course 1 bar is close enough to call it 15 PSI.
I’m running straight 30 weight and that may increase oil pressure a little.

The alarm is set really low like just a few PSI if memory serves.
My 4JHE is an 87 model with about 1200 hours or so on it.

I don’t think you have a real problem, it’s just showing its age a little. Most people don’t have an oil pressure gauge and are happy if the alarm doesn’t sound.

[billknny]

Originally Posted by cgebluewater

I recently installed a Yanmar oil pressure sending unit and gauge on a 1986 Yanmar 4JHE. When the engine is cold the reading is at 4 bar which is 12 o'clock straight up at idle and at all rpm ranges. after the engine runs long enough to get the oil temp up to operating temp the oil pressure maintains 4 bar until rpm drops to about 2000 rpm, about 3 bar at 1800 rpm, about 2 bar at 1500 rpm, and about 1 bar at about 1200-1300 rpm which does not bother me to much. But what concerns me is that the gauge is just hardly above zero at idle of 750 rpm. Is that enough oil pressure at idle ?

The low oil pressure alarm is operable but does not alarm at idle. it does alarm when the engine is stopped with key on or before startup with key on as it should.
I changed the oil and oil filter to make sure the oil was not thinned for any reason. the oil pressure readings where exactly the same after the oil and filter change using Shell Rotella triple protection multi-viscosity 15-40

A couple of things...

If the oil pressure really is "barely above zero" that would be a problem. As others have suggested, it MIGHT be a gauge problem, but your other readings are normal, so the gauge is an unlikely culprit.

Try running the engine with straight 30 weight oil. Unless you are running in very low temperatures there is no reason to go with the 15w-40 grade.

I am assuming that you aren't losing oil...

Installing a temporary mechanical gauge would be a worthwhile exercise, just to prove the gauge as right or wrong.

Your pressure switch that runs the alarm should close at ~1 bar. You can bet the engine that it is right and the gauge is wrong... or you can check it...

[a64pilot]

Actually the low oil PSI warning is very low pressure. I found the specs in the electrical portion of the engine manual, a screen shot is below.

[Lepke]

A single grade oil would give higher pressure because it doesn't thin as much when hot. I don't think you gain much with a mulit-grade on a 30 year old engine. If STP was still around you could add that. Pours about like honey.

I would use a mechanical gauge at the engine to check the real pressure. A new electric gauge should be ok, but they're affected by voltage and any ground problem. The main and rod bearings would be the most likely failure and those bearings aren't much different than reciprocating steam engine bearings and they were oiled by drip or wick. No pressure at all. Old reversing diesels had only a couple pounds of pressure at idle. I never ran a new one so don't know what they started with.

[cgebluewater]

Originally Posted by a64pilot

Actually the low oil PSI warning is very low pressure. I found the specs in the electrical portion of the engine manual, a screen shot is below.
Attachment 177981

So if the oil pressure light and buzzer are designed to alarm all the way down at 0.1to 0.3 would it be reasonable to assume Yanmar is OK with the oil pressure above that range at idle ?


I appreciate all the responses. I think I will switch to Rotella T1 SAE 30 and see if the pressure stays a bit higher when up to operating temp at idle RPM.
As a bit more info, engine does not burn or leak oil. I do not need to add oil between oil changes. Also sent oil sample to blackstone lab and results were all within spec for this engine and no sign of metals that would indicate bearing wear. Also engine sounds smooth and runs strong. It pushes a 14 ton monohull at about 7 knots at maximum RPM (3500 RPM) and cruises at 6 knots at 80% power(2900 RPM) with boat & tanks fully loaded. I also did compression check which indicates good compression across all four cylinders and all with 20 PSI of each other.

[Kenomac]

We had a similar issue six years ago, frustrating, but it ended up being the wire going from the sending unit to the gauge which was the problem. Yanmar motor.

[Tayana42]

cgebluewater, I had the same concern with my 1989 Yanmar 4JHE. I learned from knowledgeable people on this forum that the low pressure at low rpms was not a problem. Nevertheless, I installed a mechanical oil pressure gauge permanently mounted near the engine to double check the pressure shown at the instrument panel. I also use straight 30 weight oil. No problem and I’ve been running the engine this way for 18 years.

[a64pilot]

Originally Posted by cgebluewater

So if the oil pressure light and buzzer are designed to alarm all the way down at 0.1to 0.3 would it be reasonable to assume Yanmar is OK with the oil pressure above that range at idle ?

That is my assumption, or you have to assume they aren’t smart, and I don’t assume that. I think they know what they are doing.
Your lowest pressure will be seen when you bring her from idle after a long hard pull, due to the oil being hottest then.
Multi viscosity oils are of course designed so that they hold a stable viscosity through hot and cold. It’s my opinion that we don’t often run our motors in well below freezing weather, and not at oil temps well above 100c, where a multi viscosity oil is called for, so we should use straight weight oil.
Turbo’s are an exception, if they are not water cooled, then they are oil cooled and can dump significant amounts of heat into oil, and a multi vis oil is called for with a turbo motor, in my opinion.

Of course there ain’t no such thing as a free lunch, and a multi vis oil breaks down its viscosity improvers much faster than a straight weight oil.
Synthetics are different, they can and often act like multi viscosity oils, but don’t have to have the viscosity improvers to do that, so that they don’t break down, not for very long intervals.
However we change our oil due to soot build up, not the oil breaking down, so not much to gain with a Syn oil.

In short, your best bet, in my opinion is to run straight weight oil and change it every 100 hours. Yes that’s early, but oil is at its best when it comes out of the can and then slowly begins to load up with soot, and soot is acidic and abrasive, so how much soot do you let build up before it needs changing?
Add into that, the older a motor is, due to inevitable blow by, the faster the soot builds up, so the older a motor is, the more frequent it’s oil changes should be.

[GRIT]

I'm going to disagree with A64.

My job used to be to keep heavy equipment running, at a profit. And a multi-weight oil, especially synthetics, are the best thing for a diesel engine.

A multi-weight oil is the best thing for you. A 15-40 oil acts like a 15 weight oil when it's cold, and a 40 weight oil when it's hot. Meaning it's more stable in it's viscosity. Putting a 30 weight oil in is not going to do your engine any favours.

Older engines tend to have a lower oil pressure, especially noticeable at lower RPM. I've seen many older engines with idle pressure around 0.3-0.5 bar

Check your pressure with a mechanical gauge, and get an accurate reading.


Cheers.
Paul.

[a64pilot]

Paul, reason I say most of us Boat guys don’t need multi vis oil is we have a tendency to stay in shirt sleeve weather, a cold day is 50f and a hot one 90f.
Then our motors don’t get hot, not hot at all. Measure your oil temp, I have shot the oil filter at cruise on my 4JHE and it is around 165 or so, right about coolant temp.
A modern automobile as a reference point oil temps run in the low 200’s , up to as high as 220 or so at highway speeds.
So we don’t get cold enough to need 15W oil, and our engines never hit temps high enough for a multi vis oil to act like a 40W either.
A good Syn oil never hurts contrary to what some will tell you, it’s just that in our normally aspirated engines, assuming you like most only cruise at low 2000 to 2500 RPM on a 3600 RPM motor, it’s just not needed.
I used to run 5W-40 Rotella T6 myself and then decided to go to straight 30W.
Now if you work one hard, and especially if you only charge oil at the factory recommended interval, then Syn may be for you.

[GRIT]

Hi A64, I'm still going to disagree with your opinion on this one.

A 15-40 oil will circulate through a cold engine (cold, as in not started in 24 hours) faster than a 30 weight oil, no matter the ambient temperature. This is especially important in an older engine, as most engine wear (on normal use engines) occurs at startup. It's a common misconception that engines wear the most when they're pushed.
Also, once the engine gets warm, even at 165F, the 15-40 will outperform a 30 weight oil.

There are very few engine manufacturers that will have a straight weight oil listed as their recommended oil. (I don't know of any, but there may be some.) That's because the multi weight oils simply outperform them. Many manufacturers now recommend synthetics, simply because they leave "Dino" oil in the dust, as far as performance goes. I don't know about the USA, but in Canada, it's pretty hard to find a 30 weight oil, nearly every oil on the shelf is multi weight, or multi weight synthetic.

I'm a big fan of synthetic oil, and one of the reasons is exactly the opposite of the reason you pose. I don't mean to be argumentative here, but a diesel engine that's run lightly, as most sailboats are, is as hard, or harder, on the oil than one that's run hard. There are more contaminants getting by the rings, and into the oil on an engine that's run "soft". Which is why so many folks recommend running the engine hard for about 10 minutes every hour or so.

We always ran the best oils in our rigs, and we had several of them that went nearly a million miles without a rebuild.

A boat's not a truck, and I would argue, that with most boat engines running for short periods, and barely getting to operating temperature (165 is pretty low as an operating temperature, 180-185 (80-85 Celcius) is much better for the engine.) a good multi-weight, or synthetic is even more important to keep the engine working for a good long time.

I would recommend someone spend twice as much on synthetic oil, and change their oil half as often, than spend money on cheap oil and change it twice as often.

I personally don't change my oil until I have 200 hours on it. Unless it's a new engine, and within it's break-in period. Though I always use synthetic oil, and brand name filters.

I enjoy reading your posts A64, and I hope I can change your mind on this matter.

Cheers, and be well.

Paul.

[GRIT]

I forgot to mention.

1. Low oil pressure is a symptom, and raising the pressure with a thicker oil is not the cure.

2. 30 weight is not thicker than 15-40 at operating temperature.

3. The goal is to have good lubrication throughout the engine, "pressure", in this case, is a resistance to flow.

4. Oil pressure is an indicator of what's happening in your engine. Having oil pressure read at a certain level is not the goal.

Cheers.
Paul.