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