Author Topic: Yanmar 4JH series oil related questions  (Read 1377 times)

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  • Nirvana - H46 #13
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Re: Yanmar 4JH series oil related questions
« Reply #8 on: May 17, 2018, 02:04:13 PM »
Actually the oil pressure is measured at the block by the oil pressure “sender”.  The Sender gains resistance as pressure rises.  The guage at the panel is ‘electrically’ connected to the sender and displays the measured resistance in analog form. 

You can inspect the sender which on the JH series engine is located above and aft of the filter on the block.  [ref. Yanmar user manual for JH series marine engines Section X II & Yanmar JH Service manual Section 1-3,4,5 “Views” and the piping diagrams on Sections 7-1,2,3,4 covering the four JH series engines]

You can also see the electrical path via the wiring diagrams for the various panels in section 9 Electrical 9-3,4,5,6 for the various engine/panel configurations.  These note the “L. O. Pressure Switch” (electric pressure {resistance} limit trigger switch)  if you have a guage on your panel the Switch (on the block) will have been replaced with a sender.

There is no pressure drop between the engine and the guage, it is electrical.  That would be a very bad design as you risk oil leakage at and between the panel and block.  Additionally head (rise/run) does not reduce pressure in oil, oil and liquids do not compress thus no loss.

Low oil pressure should be attended to.  Typically low oil pressure results from clogged filters, pipes, or wrong/bad oil.  On rare occasions may be a result of a bad oil pump but this is difficult to determine without removal and inspection.  Also though minorly, your crank shaft actually contributes to oil pressure.

I can post page copies of the notes diagrams if anyone is interested.

Ken Sabatini
Nirvana - ‘97 Hylas 46 #13


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Re: Yanmar 4JH series oil related questions
« Reply #7 on: May 01, 2018, 03:21:38 PM »
low oil pressure at the gauge has been discussed for years - 15 to 20 plus!

Think about it - oil is thick and its viscosity increases when cold, which is why we use a multi viscosity oil.  However, oil in the small diameter tube rarely moves and the gauge is located 10 feet above the engine.  Normal oil pressure in an engine runs 15 to 30 pounds at 2000 RPM, to a max of 30 to 60.  At idle, the oil pressure maybe as low as 7 PSI.

So for ten feet you loose 4 PSI of pressure - which results in a pressure reading of 3 PSI.  Gauge has 5 PSI increments which means its at best within 2.5 PSI of accuracy with interpretation.

Typically we start the engine with the buzzer singing - no/low oil pressure; after 15 sec + or - ; the buzzing stops and the needle on the oil pressure gauge begins to rise.  Finally after 30 + seconds the needle on RYA lands on 15 PSI on a fast idle - 1000 RPM.

As to what oil And Fuel to use:  Cheveron Delo 400 and Chevron Diesel are perhaps the best combination.

For Diesel fuel - the Techtron in Cheveron or 76 will keep the engine much cleaner: intake manifold, exhaust manifold, combustion interior and injectors.  Hands down!  And yes - this has a direct, major impact on engine life!!!

As to oil - it's most important to be consistent - if you use Delo 400 Great, if you use shell Rotella Great - But be consistent, don't change.  Diesels are plow horses.  Keep the schedule and food/oil the same and they will run for ever!!!

Have a friend with a Yammar Pump Engine - 10,000 hours and still running strong using Amsoil !  The big advantage is that he changes the oil every 250 to 300 hours or double the life of petroleum oils.  Oh and he only burns Cheveron Diesel!!!

Andy McCann
s/v RYA,  H49/#26


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    • Quintessa
Re: Yanmar 4JH series oil related questions
« Reply #6 on: April 20, 2018, 09:16:37 AM »
I would start by trying the Yanmar branded oil or an oil with the same spec.  I have found the Volvo VDS 3, 15W-40 oil to provide good pressure and have low consumption.

As for the remote oil filter question, having installed a remote system on another diesel I can say that although the remote filter can be more convenient, it can be a lot of trouble to install especially if you don not have a good place to locate the remote filter.  You are also introducing more failure points in the high pressure oil lines and fittings.

I would try to develop a good technique for changing the horizontal filter.  The best procedure I have found is to locate a 250ml cup (epoxy mixing cup works well) under the filter. I give the filter about a quarter turn to loosen it then punch a hole in the side with an ice pick. I give it another half turn and punch another hole to let air in.  The filter drains into the cup, and after a little while I just spin it off the rest of the way.  Almost all the oil is captured by the cup.  Always a good idea to place an absorbent pad under everything before you start and will catch anything that misses the cup.

Bob Knapp
s/v Quintessa (H49-46)


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Re: Yanmar 4JH series oil related questions
« Reply #5 on: March 28, 2018, 01:14:45 AM »
Thanks for the replies. We have always used 15-40 w dinosaur oil.

John, I've been told by Yamar mechanics not to use synthetic oil in our engine. From your post I assume you heard differently?

I have tried the plastic zip lock bag trick, but when oil gets between the filter and the's tough to turn the filter off the screw mount.


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Re: Yanmar 4JH series oil related questions
« Reply #4 on: March 27, 2018, 06:16:15 PM »
Since we bought the boat (2000 H46, with a 4JH2-TE), our oil pressure gauge has never moved from "zero" at idle. It doesn't move at all until around 1k RPM, where it wakes up and pops up above the red low-pressure area (0.2 MPa). At higher RPMs, it gets up to the middle of the guage - around .4 MPa. The low-oil-pressure alarm does turn off immediately after starting the engine, even at idle while the oil-pressure gauge reads zero. I've had the local Yanmar service mechanic inspect the engine, and I don't recall him registering any concern about the oil pressure. I'm using Rotella T6 synthetic 5w40.

-John Spiegel
Vesper, H46 #30


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Re: Yanmar 4JH series oil related questions
« Reply #3 on: March 27, 2018, 02:44:34 PM »
Did you use a different weight oil with the T-4?  Can't think of any other reason for a different reading.

Here's the Shell website:


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Re: Yanmar 4JH series oil related questions
« Reply #2 on: March 26, 2018, 05:03:02 PM »
As far as the filter change...I put a plastic bag under the horizontally mounted filter and catch most of oil and then drop old filter into can get big zip lock bags from automotive websites.  I watched the yanmar tech do this and just copied him...

As far as the low oil psi reading on cockpit gauge...mine is really low too...lower than your readings at idle and 2500RPM...engine runs fine so I am choosing to ignore for now?


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Yanmar 4JH series oil related questions
« Reply #1 on: March 24, 2018, 06:57:07 PM »
Hello, we have a 2006 H49 with a 4JH3-TE engine. There are 4700 hours on the engine, it still runs good, no black smoke, starts right up, etc.

1) Have you installed a remote oil filter kit n the engine? Because of the filter location and the fact it is a horizontal mount, I usually make more of a mess with oil dripping out then I want. If you have installed a remote kit, I would love to get some specifics of your mount, or pictures, how well it works, etc.

2) We use Rotella 15-40w Diesel oil. Rotella use to be with a"T3" formulation. Now Rotella has a T4 designation. With the T3 formulation my oil pressure gauge would typically be at a 1/2 of full scale under cruising motor conditions, and about 3/8 full scale under idle conditions (assume oil is at operating temp). Now with the T4 formulation, I get just under 1/2 at cruise and 1/4 or slightly less at idle. Anyone else have similar observations or comments? Should I be concerned?


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