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OT- Yanmar marine diesel oil pressure question

Milacron

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After 8 days of cruising on sailboat, 50 hp Yanmar diesel (with only 904 hours on it) running 50 hours nonstop on offshore leg of journey and the oil pressure starts declining over a couple of hours.... from 80 to 0. The way the gauge needle was acting (needle not steady but continuous up and down readings...until eventually it was just down) I felt confident it was either the gauge or the send unit. But since I didn't know for absolute sure it wasn't a failing oil pump, I kept an eye on the engine temperature which never wavered. Ended up going another 5 hours with 0 pressure on gauge. I presume if it really was 0 pressure the engine would have seized within a minute, yes ? (in fact the reading was less than zero...bottom pegged)

The question is, does this sound more like failing send unit.. or gauge ?
 
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Check for corrosion on the connections. A bit of sandpaper or scotch Brite is the cheap and easy first step for a lot of my marine wiring issues, especially so if you are in salt water.

I have also had to replace long sections of the wire because the corrosion can creep up the length of the wire, even if the insulation is intact.
 
I'd bet on corrosion as well. What kind of sensor is it.? You may be able to hook directly to it with a hand DMM (digital multi-meter), to tell between sender and wire. It could also be both.

Is there a place to install a simple mechanical oil pressure gauge?

One trick when attaching crimp terminals for use on boats and road vehicles is to flood the stripped wire with silicon grease before insertion into the terminal and crimping. The crimping force will squeeze the grease out of the crimp nugget, which is in fact airtight. The grease still fills the gaps between wire strands. Then strengthen and seal the crimp area by installing the kind of heat-shrink tubing where the inside melts and glues itself to both the wire insulation and the crimp barrel.
 
Sender or wire would be my bet too.

Shit like this is why I have a Murphy Switchgauge mechanical oil pressure gauge fitted to my marine diesel as well as the electric pressure gauge, AND an oil temp gauge as well. I've seen an electric oil pressure gauge stop working and trigger the low oil alarm at a bad time when the pressure system was perfect, just the sender went tits-up. So I duplicated mine.

PDW
 
It sounds like either corrosion (as others have stated), or a bad sending unit.

To test your gauge, simply ground the wire that goes to the sender. If the gauge pegs at max pressure, it's good and your sender is bad (or the wire in-between the gauge and the sender is bad or corroded).
 
Qt Joe Gwinn (Is there a place to install a simple mechanical oil pressure gauge?)
Likely the sending unit...But
Very definitely a view readable oil pressure gauge should be added.
A T at the oil gauge can also have a stop engine/ or low pressure to sound a warning sound..

Seems like tractors and boats often have poor battery ground, good to add an extra ground wire IMHO (not likely part of your oil pressure problem).

 
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I suspect that the rolling action of a boat would oil the engine bottom end like the old splash and dip oilers in early engines, so as not to have as great a potential total failure as a stationary engine as ling as the crankcase was up to level. Some auto engines had a filter screen failure that could stop the oil pump and ruin an engine with zero oil pressure.
Do let us know if it was a sending unit failure
 
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Seems like tractors and boats often have poor battery ground, good to add an extra ground wire IMHO (not likely part of your oil pressure problem).
Yes. I had that with an old Volvo, model 240 (or 850?) if memory serves, where the fuel pump ground wire connection to autobody steel had rusted out from splashed road salt. (The fuel pump was inside the gas tank, and it required removal of the tank to access the pump.) The solution was to lengthen the ground wire and route it to inside the trunk, making the connection to steel where both sides were in a protected and dry place.
 
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After 8 days of cruising on sailboat, 50 hp Yanmar diesel (with only 904 hours on it) running 50 hours nonstop on offshore leg of journey and the oil pressure starts declining over a couple of hours.... from 80 to 0. The way the gauge needle was acting (needle not steady but continuous up and down readings...until eventually it was just down) I felt confident it was either the gauge or the send unit. But since I didn't know for absolute sure it wasn't a failing oil pump, I kept an eye on the engine temperature which never wavered. Ended up going another 5 hours with 0 pressure on gauge. I presume if it really was 0 pressure the engine would have seized within a minute, yes ? (in fact the reading was less than zero...bottom pegged)

The question is, does this sound more like failing send unit.. or gauge ?
You continued to run the engine with falling oil pressure and the only check you did was the coolant temp? Given your mechanical knowledge I expect you did something more?
It’s only a little yanmar but will still cost a bit to replace if killed.
 
You continued to run the engine with falling oil pressure and the only check you did was the coolant temp? Given your mechanical knowledge I expect you did something more?
It’s only a little yanmar but will still cost a bit to replace if killed.
unit has an engine block temp sensor .. and the way the gauge needle was bouncing around I thought 95% chance it was electrical problem . Plus what I do really … 30 miles offshore at night and not enough wind to sail only., I do have Sea Tow account but doubt they would come out that far
 
unit has an engine block temp sensor .. and the way the gauge needle was bouncing around I thought 95% chance it was electrical problem . Plus what I do really … 30 miles offshore at night and not enough wind to sail only., I do have Sea Tow account but doubt they would come out that far
Understood.
Bouncing around of a pressure gauge can also be caused by the movement bringing the suction out of the fluid. Usually caused by a low level. Sometimes because it’s just that bloody rough!
My main worry with a falling pressure on a Diesel engine is fuel contamination. Can lead to lots of issues and a particularly large bang if not attended to. Haven’t had the bang yet but have had the odd one full of diesel.
My favourite was when my highly paid and very qualified 2nd mentioned casually that he was a little puzzled by one of the generators, he had to drain some oil out of it twice as it kept on showing over full…..
 
Well worth the time and effort to put a T in the block at the sending unit, and install an additional glycerin filled gauge (vibration damped) right on the enigne for backup verification.
My feelings exactly. In the case of any future electrical gauge failures it could relieve a lot of anxiety.

As for the sender/gauge testing, I wouldn't short the gauge directly to ground as it might damage the gauge. Most analog senders (vs a simple pressure switch) vary the resistance with pressure. I'd check the sender first with an ohmmeter or even a small test light.
 
In trying to determine the Yanmar part no. I'm a bit confused by their descriptions. In attached picture, the defective unit is lower right and in drawings described as "sender, boost" and the upper left unit as "sender, oil pressure". And seeing as this is a naturally aspirated engine the "boost" moniker makes no sense. Thoughts ?

The model engine is 4JH2E.

IMG_3516.jpg
 








 
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