Install mechanical oil pressure gauge for Yanmar 4JH2E

[smokey73]

I have a 1994 Hunter 40.5 with a Yanmar 4JH2E. Engine runs great, starts immediately when the key is turned on, no smoke on running, even at high rpm.. When the key is off, the oil pressure light in on and the alarm sounds as it should. The oil pressure indicates at the low end of the green range when running at cruising rpm (2200 to 2800 rpm). When I increase rpm, however, the oil pressure decreases substantially. The oil pressure alarm does not sound though. I want to check the actual pressure using a mechanical gauge. I wouldn't mind having a T type fitting so I can put the mechanical gauge down at the regular oil pressure sensor point and still have the electronic sensor installed. So I have a couple of questions.

1. Does anyone know what size/type of fitting would be necessary to install. Size and type of thread to be compatible with the sensor port on the engine? (NPT or straight thread and size, etc.) If you have done this do you have a picture?
2. Recommendation for an mechanical oil pressure gauge to use

3. Does anyone have any thoughts on why the oil pressure would decrease at higher rpms rather than increasing. I am thinking it might be the oil pressure relief valve that is a part of the oil pump/filter assembly.

Inquiring minds want to know?

 

[Don S/V ILLusion]

3. Does anyone have any thoughts on why the oil pressure would decrease at higher rpms rather than increasing. I am thinking it might be the oil pressure relief valve that is a part of the oil pump/filter assembly.

Inquiring minds want to know?

not that this helps but welcome to the club.

The boat engine we used to have (4JH2) exhibited similar behavior. When I attended a Yanmar engine maintenance training class, I asked the instructor why. His response was uninformative except to say it’s ‘normal’ and be concerned only if the pressure drops below 20psi at the gauge.

 

[smokey73]

@Don S/V ILLusion I have a hand written note in my Yanmar 4JH2E manual that says something similar to "from Mac Boring (sp)". I would guess that my indicated pressure on the electronic gauge is below 20 psi when wide open. Did the maintenance training class say what to be "concerned" about if it is below 20psi. That is why I want to check it with a mechanical gauge - to see what it actually is.

 

[Don S/V ILLusion]

I just found my notes:

“anything below 20psi requires attention.

The two suspects causing low oil pressure are 1. Oil pressure control valve pressure regulator on the filter housing or 2. Lube oil pump on gear case side engine plate [ cannot be disassembled - replace] The lube oil pump pressure reg valve on filter housing is factory set to maintain a 40 psi pressure. It is adjustable.”

if it were me, I’d do what you said - verify pressure with external gauge first before pulling out the tool box.

i still have the old 4JH service manual if you need blow-up pictorials of parts locations.

 

[Rick D]

I chased the same issue for a couple of years and hundreds of dollars. I replaced the sending unit, the gauge, ran a cheater wire, checked the ground, etc. Someone else can weigh in, but I believe the thread is British Pipe Thread (good luck finding any adapter). I finally got a mechanical gauge and jam-fit an adapter. It read 40 pounds on the gauge when hot. I gave up. BTW, I think I found a VW Rabbit had the same threads, but that was fifteen years ago, so I may be wrong. Also, check that the warning buzzer / light may be on a separate sending unit.

 

[smokey73]

@Rick D I think I found an adapter that would allow both my 1/8 in BSPT sensor and a 1/8 in NPT oil pressure gauge to be attached. Does this look like it would work?

1/8" BSPT Oil Pressure Sensor Tee to NPT Adapter Turbo BSPT Adapter Engine Gauge | eBay

Inlet Thread Size: 1/8” BSPT Male. Outlet Thread Size: 1/8” BSPT Female. Center Tap Thread Size: 1/8” NPT Outlet Female. Works with most Honda, Subaru, Toyota, Hyundai, Mazda, Suzuki and Mitsubishi oil pressure senders.

www.ebay.com

 

[Rick D]

@Rick D I think I found an adapter that would allow both my 1/8 in BSPT sensor and a 1/8 in NPT oil pressure gauge to be attached. Does this look like it would work?
Sure, why not try? Certainly cheap enough.

 

[RitSim]

Also try McMaster.com search for "bspp-to-npt pipe fitting adapters"

 

[Hello Below]

You may find that the sensor thread is an M10. Here is an old article that may give you some insight.
Upgrading Yanmar oil pressure gauge and sender - Ocean Navigator

 

[smokey73]

@Hello Below Thanks for the link. I'm still a little confused as the article doesn't specifically say it is a male 1/8 BSPT or a male 10-1 BSPT. I've found adapters for both 1/8 inch BSPT male to 1/8 in NPT female and also 10-1 BSPT to 1/8 in NPT female. Not sure which one is correct. Anybody out there have an authoritative answer?

 

[smokey73]

I purchased a non-yanmar sender and gauge to install as described in post #9. When I hooked up the new gauge I still don't have a reading so I went down to the new sender and took resistance readings with the gauge disconnected. The specified readings as per the spec are:
PER THE SPEC:
0 psi 240 Ohms
40 psi 103 Ohms
80 psi 33 Ohms

I read 240 Ohms with the engine off so that would be 0 psi (which is what I'd expect)
At Idle it reads 110 Ohms right at the sensor output, so pretty close to 40 psi
At about 3000 rpm it reads 72 Ohms so I'm guessing about 60 psi.

All that seems to show that my oil press is where I'd expect it to be and I don't have any actual issues with low oil pressure when running at high rpm. The problem is that when I hook up the new gauge it reads 0. My old gauge read just below the green band when at idle but fell to near 0 when at high rpm. My assumption is that there is excessive resistance or now an open somewhere in the electrical wire between the sensor and the gauge. Does that seem reasonable? If I can figure out how to route it I might just run a separate new wire from he sensor to the gauge in the panel at the helm.

Any insights or thoughts about where I might be wrong would be appreciated

 

[Ralph Johnstone]

Why not run a temporary #16 or smaller from the sensor to the new gauge and leave it taped up to ensure nothing else is going on while you take it out a few times ?

My old gauge read just below the green band when at idle but fell to near 0 when at high rpm.

Seems odd for a wiring problem if it did that everytime.

The problem is that when I hook up the new gauge it reads 0.

Now I'm starting to get a headache .

Get the temporary, both (+) and (-) wire installed and forget EVEYTHING you have seen so far. Something or somebody is not quite right here.

 

[smokey73]

Why not run a temporary #16 or smaller from the sensor to the new gauge and leave it taped up to ensure nothing else is going on while you take it out a few times ?

@Ralph Johnstone Sounds like a good idea. Easy to do and checks to determine if the wire alone is the problem. I have plenty of spare #16 wire to do that test. If it works I'll either check continuity in the existing line and resistance and correct as needed or just figure out how to route the new wire.

 

[dLj]

Reading through this thread, I'd see if you can check the gauge. It was not running properly when you started, it still isn't. Jut a thought.

dj

 

[smokey73]

@dj, it is a brand new gauge that is "matched" in resistance to the "new sensor." The old gauge is in the pile of stuff to give away or to toss. I think the gauge works fine but not so sure about the sensor. I should have checked the sensor resistance at the sensor before I replaced it but the replacement "non-yanmar" sensor and gauge were only about $80 total.

Anyone want a spare original Yanmar Oil Pressure guage and sensor? Yours for the asking, just pay postage. PM me if interested.

 

[dLj]

@dj, it is a brand new gauge that is "matched" in resistance to the "new sensor." The old gauge is in the pile of stuff to give away or to toss. I think the gauge works fine but not so sure about the sensor. I should have checked the sensor resistance at the sensor before I replaced it but the replacement "non-yanmar" sensor and gauge were only about $80 total.

Anyone want a spare original Yanmar Oil Pressure guage and sensor? Yours for the asking, just pay postage. PM me if interested.

My misunderstanding - thought you were using the same gauge....

I just sent you a PM.

dj