Oil Pressure Issues

Hello
My single engine trawler is equipped with the 160 4LHA-HTP Yanmar. The engine has 540 total hours since new. The other day while cruising at 2000 RPM, (engine water temp at 170ºF) I noticed a fluctuation in oil pressure between the 4.5 and 3.5 numbers (X10 MPa) on the gauge. When I reduced the power to idle the oil pressure went to near zero, but neither the red warning light or alarm came on. When I pulled out of forward gear to neutral, the oil pressure went back up to the 2 at idle RPM of 750. When shifted back to forward gear at idle the oil pressure would then go back down to near zero. Funny thing, when placed in reverse the oil pressure would only drop a small amount. When the throttle is pushed up in either gear or in neutral the oil pressure rises to normal range of 4.5 with the intermittent fluctuations. Also, these readings are the same at both helm and flybridge instruments.

Could this be the oil pressure sending unit or something worse? Does the red oil light and alarm work on a different circuit than the gauge? A Google search did find problems with some Yanmar oil pressure sending units on other model engines. Thanks. SteveH

What was the RPM when it went almost to 0. Is this the first you noticed?

On our 671 at low idle 500 rpm the oil pressure almost goes to 0 and the alarm sounds. At about 750 rpm the pressure comes up and alarm turns off. So it could be the rpm is to low?

Check all your connections. They do vibrate loose. A loose connection at the sender could give fluctuating readings.

look for the simple things first.

SD

SteveH said:

Could this be the oil pressure sending unit or something worse? Does the red oil light and alarm work on a different circuit than the gauge? A Google search did find problems with some Yanmar oil pressure sending units on other model engines. Thanks. SteveH

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The red light and the buzzer probably only come on with the lack of all oil pressure. So some pressure would keep them from coming on. That is why they are not accurate. Low pressure at 1,500 rpm can be hell on bearings but the light may not come on because it had 3 lbs positive pressure and not the 45 lbs needed to keep the bearings from self destruction.

The sensor can't be that expensive to replace.

Depending on how the engine is set up, it may be a sender issue. Some engines have separate senders for the alarm and each station gauge. If yours has a single sender for both station gauges but a separate one for the alarm, it would explain things sort of. I.e., you may have a faulty gauge sender but the alarm sender may be fine. Or the engine really is in trouble but the alarm sender is kaput. I'd put money on the former but definitely check it out.

The alarm and red warning light seem fine. At start up the red low oil pressure light and buzzer alarm are on for a second or two, then both go out, shortly followed by a rise in gauge oil pressure indication. All seems normal except the gauge oil pressure reading drops to near zero when at idle and in forward gear until RPMs are increased. I do plan to check for loose connections at the oil pressure sending unit. Maybe disconnect all wire leads clean them up and reconnect. Thanks for the ideas. - SteveH

Steve,

Some Yanmar diesels are known to have problematic oil pressure sending units. A few owners have reported having to change them almost annually. At over $100 this can get old pretty quickly. Most of the time they fail by indicating low oil pressure. On some engines, the oil pressure sending unit is mounted in an adapter known as an oil pressure damper which has a small orifice that can become clogged over time. Some have reported that cleaning the orifice has helped. The low pressure alarm and light are actuated by the low oil pressure switch which is completely independent of the gauge. Yanmar even offers a Type "B" instrument panel that relies entirely on the alarms and only contains a tachometer, no other instruments. They are known to be quite reliable, but I have not been able to find any specifications on the oil pressure switch. I do know that if that alarm sounds when the engine is running above idle, you need to shut down immediately to avoid engine damage.

I fought this issue last year on my Yanmar 4JH and tested the oil pressure with a mechanical gauge. Thankfully it was in spec so I ran it for a few months with only the alarm for warning. I finally got tired of seeing '0' oil pressure so I $replaced$ the sending unit anyway. Life's good again . . . till next time.

I would definitely check the oil pressure with a good mechanical gauge. I ordered one from an automotive speed shop. I also purchased a 3' length of Aeroquip flexible hose with a male 1/8" NPT pipe adapter to screw into the block. This also works on my generator so I have a reliable piece of test equipment that I now keep aboard.

I hope this helps you diagnose the problem.

Larry Massa
M/V Boomarang

Thanks for the info Larry. What you said provides some comfort that my problem is "indication" based. I plan to clean the connections to the sending unit and see if that clears up the problem. Although I suspect I'll end up replacing the unit in the end. - Steve

IF the Mfg approves single weight oil might help engine longevety, and oil pressures..

SteveH said:

The alarm and red warning light seem fine. At start up the red low oil pressure light and buzzer alarm are on for a second or two, then both go out, shortly followed by a rise in gauge oil pressure indication. All seems normal except the gauge oil pressure reading drops to near zero when at idle and in forward gear until RPMs are increased. - SteveH

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"All seems normal except the gauge oil pressure reading drops to near zero when at idle and in forward gear until RPMs are increased."


Might want to read the discussion 6.35 in gear idle speed when set to low. I bet the oil pressure is close to 0. You still have not said what the in gear idle rpm is?

I have the Eagle’s in gear idle, 500 rpm, set low so it’s just above maneuvering/head way speed. Check the sending unit. I still think the in gear idle rpm is to low by what you are discribing.

Hi Phil

The in gear idle is the same as it was before this issue came up. Idle in neutral is 800 RPM and in forward or reverse gear(s) it drops to about 725 RPM. Oil pressure drops from 2 (X10 MPa) to near zero in forward gear and only drops a small amount in reverse gear. - Steve

Steve, I would highly recommend a mechanical pressure gauge to check things out. It's easy to swap out and will save you a lot of time and anguish. Of course check connections first,especially the Yanmar wiring harness. Chuck

I also have the Yanmar 4J series with a bit over 400 hours with similar intermittent oil pressure readings ranging from zero to 50 psi. While servicing the engine, I found a leak in the gasket of the inter-cooler directly over the oil pressure switch. The contact on the top of the switch was corroded and damp from a very slow drip. I cleaned and tightened the contact and it seems better, but a new gasket for the inter-cooler and a new switch is on my priority list.

I don't know how insulated you are from your engine space, but on my boat one can barely perceive the engine from the lofty pilothouse. I don't trust that I could hear the engine start to hammer from a loss of oil pressure, so before I go cruising in 2013, a manifold of gauges in the engine compartment itself with a video monitor system is on my do list.

Happy day!! In an attempt to check wire connections I discovered the main wire coming from a very short lead off the Yanmar wire bundle to the bottom of the oil pressure sending unit was down to a single strand of wire. It broke off when I peeled back the rubber cap to get at the nuts. I guess engine vibration eventually cause the wire to separate due to the stretched condition of the wire. I reconnected everything, this time with plenty of slack to the wire. Started the engine and immediately got a rapid rise in oil pressure at idle RPM with no drop when in forward gear. All seems normal now. Thanks to everyone for all the suggestions. Trawler Forum is a great resource of information!!! - Steve