Low Oil Pressure

[Dave Pawloski]

I have a 1985 Hunter 31 with the original Yanmar 2GM20F diesel engine.
When I recently had the boat out, after about 20 minutes motoring at 1800 rpm, the low oil pressure alarm came on. I promptly shut down the engine, sailed the boat back to the marina, and restarted the engine (no alarm) for about 5 minutes to get back into my slip.
The next day,for the easiest, and first potential "fix" I changed the oil (SAE30) and installed a new oil filter.
I again ran the engine under load, and after about the same time duration and rpm level, and again the low oil pressure alarm came on.
1. The next "fix" I guess will be changing the oil pump. The troubleshooting guide in the Yanmar manual states "see your Yanmar dealer" for oil pressure issues, and the diagrams in the manual are somewhat cryptic as to where it is located.
HAS ANYONE EVER CHANGED THEIR OWN OIL PUMP, AND WHERE IS IT LOCATED ?
2. As the boat (and engine) is 32 years old, I suppose the possibility exists that there are issues with the piston oil rings or the bearings, although I am not seeing any evidence of excessive oil consumption, smoke, loss of compression , difficulty starting, or excessive engine noise or vibration.
What has me most perplexed is that the problem does not occur until about 20 minutes of run time at 1800 (or I presume higher) rpms.
WHAT IS THE ENGINE TRYING TO TELL ME ???

 

[Justin_NSA]

I didn't even know they had pressure alarms. Just temp

 

[justsomeguy]

The next "fix" I guess will be changing the oil pump.

How about checking/replacing the lube oil pressure switch?

 

[Whatfiero1]

Yea they have pressure alarms that's what comes on when the key is turned on before the motor is started. I'd ground out the switch first. Or disconnect it with key on first to check for bad switch then check filter or you already changed that. Then try 50 wt oil

 

[Warren Milberg]

A few random thoughts as these kinds of problems are hard to diagnose from afar:The first thing I would do is make sure your oil level is full - before starting the engine and after the low oil pressure alarm sounds. When you changed the oil, did you extract the full amount of oil (about 2 litres)? If not, look for leaks. Second, make sure you are not leaking diesel fuel or water into the oil pan and diluting the oil there. Suck up a few ounces of engine oil and put it in a glass jar and see if there are any layers that shouldn't be there. Third, I'd unscrew the oil filter and make sure the hole in which the filter screws is not clogged or dirty. Clean the threads and use a Q-tip in the hole. Make sure the engine oil filler cap threads on top of engine are clean and tight. Make sure the rubber around the dipstick is in good condition given the age of the engine.
Finally, I'd replace the oil pressure sending unit with an OEM Yanmar unit. Good luck with this.

 

[kloudie1]

The oil pressure switches do go bad so an option would be to install a pressure gauge either temporarily, or permanently .. A bad switch would be the most common cause of the alarm. The Yanmar spec for the switch indicates that it turns "ON" at 1.4 to 4.3 PSI. this is the switch:
http://shop.toadmarinesupply.com/ships_store/?p=details&mfc=Yanmar&sku=124060-39452&sectionid=
A wire short can do that but usually it alarms all the time and not after a run. Another thing that can cause this is a small piece of debris in the oil pressure control valve. The valve is in the threaded piece that the filter screws onto.
The oil pump is inside the front gear case cover so replacing it is a pretty big job.. Requires removing the injection pump and crank pulley and messing with the governor..

 

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[Rick D]

I have had a low indicated pressure for a long time. A common issue on my generation of engine. I got a mechanical gauge to test it and all read normal. It's in the sending unit of gauge or wiring. At least I feel better knowing it's not a real issue. Good luck.

 

[Jim 5757]

DEFINITELY! check actual pressure with an accurate gauge before doing anything else!

 

[HMT2]

Had the same thing happen. Before you change the oil pump, change out the the oil pressure sensor for the idiot ligh/alarm , it is cheap and easy and what we did on our '83 H31 four years ago and no worries since.

 

[Captn Scotty]

sounds like after 20 min it comes up to a temperature that sets off the sensor, probably a bad sensor?(fingers crossed)

 

[MitchM]

as i recall that yan has both an oil pressure sending unit and an over temp alarm. with engine off, locate these units on the block. as i recall one is a screw out fitting (pressure sending unit and one is a wired connection. low oil level means the temp in the block goes up past acceptable levels , and the temp alarm goes off. so you definitely need to shut down the engine . go to boat diesel.com and pay to become a member, to see the 2 GM 20 F manual and parts diagrams, and browse the 2GM20F trouble shoot posts . with your new knowledge, remove and clean both units. that will be cheaper than one trip to your mechanic. thy are simple to replace. it sounds as though the temp alarm is functioning OK. it comes on, as it should when the ignition is on, then goes off, then goes on again because temp rises as an insufficient amount of oil is not lubricating the engine to design specs. the oil pressure sending unit is also an easy replacement.

 

[Benny17441]

Don't jump to conclusions. Checked oil level and new filter, is the engine overheating or do you hear valve train trashing noise? If engine is running normal it might just be a sensor problem or more likely an electrical wiring problem. The oil sensor when it encounters low oil pressure it will close a circuit that turns on the buzzer alarm and the oil warning lamp. A short circuit in the wiring or the sensor will also close the circuit which will trigger a false alarm. Check the wiring harness from engine to control panel and make sure all the connections are clean and tight. The wiring harness in these old Hunters is routed around sharp fiberglass bends and with many years of hull flexing the insulation of the wires in the harness can chaff and cause and play havoc with the warning and starting circuits. Usually a visual inspection of the harness especially at the bends will indicate if this could be the cause. If I narrow the problem down to the oil sensor I do not bother conducting tests I just go ahead and replacle it. Last will I consider a faulty oil pump and only if the engine is giving signs that something is afoul. A higher SAE oil will raise the oil pressure . A 30 year old engine should be running no less than 10W40. A higher SAE also raises compression and curtails oil consumption.

 

[Bill Roosa]

To check if the problem is the wiring or the sensor just pull the wire off the low oil pressure switch. If the switch is bad the alarm will stop because the circuit is not grounded. If you still hear the alarm (engine running of course) the the problem is certainly in the wiring. alternately you can pull the wire and measure the resistance between the switch terminal and ground (with the engine on) it should be infinite resistance or open.

 

[Dave Pawloski]

The oil pressure switches do go bad so an option would be to install a pressure gauge either temporarily, or permanently .. A bad switch would be the most common cause of the alarm. The Yanmar spec for the switch indicates that it turns "ON" at 1.4 to 4.3 PSI. this is the switch:
http://shop.toadmarinesupply.com/ships_store/?p=details&mfc=Yanmar&sku=124060-39452&sectionid=
A wire short can do that but usually it alarms all the time and not after a run. Another thing that can cause this is a small piece of debris in the oil pressure control valve. The valve is in the threaded piece that the filter screws onto.
The oil pump is inside the front gear case cover so replacing it is a pretty big job.. Requires removing the injection pump and crank pulley and messing with the governor..

 

[Dave Pawloski]

Hi all, and to thanks to those who replied to my query with suggestions.
I have changed then oil and filter, and the oil pressure sending unit with no results.
I subsequently have had two different mechanics to the boat. Both connected external pressure gauge directly at the sending unit, and ran the engine under load well until it had heated up.
Gauges showed oil pressure holding steady well within acceptable parameters, so the problem is clearly within either the wiring or the alarm panel. Working on solving that next, but at least no major problem exists within the engine.
Again, thanks to all.

 

[pateco]

On my H31 with the 2GM raw water cooled, I have been getting the oil pressure alarm only upon restarting after a sail. When I am restarting in preparation for dropping my sails the alarm stays on for a good 20 seconds before finally shutting off. My thoughts are that sailing at a heel on starboard tack, (what we are usually on when returning to our inlet) the oil is running to one side of the engine exposing the low oil sensor. I am due for an oil change, so I will check the level when that is done.