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Author Topic: Oil Pressure Alarm  (Read 1167 times)

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Oil Pressure Alarm
« on: June 27, 2016, 06:46:01 AM »

I've got an M25XPB and have been having a low volume/faint but persistent oil pressure alarm sound from the panel when operating at some rpm's between about 1700-2000 and then again around 2500, but not if I increase to 2600.  The oil pressure gauge shows normal pressures between 30-60psi. The oil level is normal and I haven't had any issues with the engine otherwise.

I'm pretty sure the issue is with the low oil pressure alarm since the sound is a faint pulsating alarm as opposed to the continuous signal of the water temp alarm. In any case, water temp is also good, always staying below 160F.

Could my low oil pressure alarm be faulty? Is there another issue I can investigate?  Hearing the alarm, faint as it might be, is stressful even after I've confirmed oil level & pressure and water temps in spec via gauges. 
'87 C34 TR/WK M25XPB

Jim Hardesty

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Re: Oil Pressure Alarm
« Reply #1 on: June 27, 2016, 08:07:51 AM »

First thing I would try is the connector on the oil pressure sending unit.  Should be clean and tight.  If that doesn't fix it  just change the sending unit.  I may be wrong but I think you can just pull off the old one and match it at an auto supply store. 
Jim Hardesty
2001 MKII hull #1570 M35BC  "Shamrock"
sailing Lake Erie
from Commodore Perry Yacht Club
Erie, PA


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Re: Oil Pressure Alarm
« Reply #2 on: June 27, 2016, 11:49:00 AM »

Oil switches do go bad.

Is the switch a 1-wire or 2-wire?  On the engine block, or mounted on a tapped block fed from a hose?  A repower by any chance?

Though the 'standard' is a normally-open, 2-wire, 1/8 x 27 npt, switch off the engine block -- but I know of an XPBs that has a 2-wire normally-closed switch, directly on the block (so it is 1/8" JIS thread, not NPT thread.)

The 2-wire N-O Westerbeke p/n 037323 switch is not that easy to find an interchange  -- the N-C closed switch is easier to cross over.

A bad connection on the 1-wire NC switch will not cause a false alarm (you can remove the wire with no effect.)
A bad connection on the 2-wire NO sw may mean the fuel pump is not running. ( Upon oil pressure it closes and powers the pump. )

If you have the 2-wire, recommend using a duralast/autozone #1053 pigtail, which includes a boot to protect the terminals (use dielectric  grease to prevent corrosion.)

« Last Edit: June 27, 2016, 11:52:05 AM by KWKloeber »
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Roland Gendreau

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Re: Oil Pressure Alarm
« Reply #3 on: June 28, 2016, 12:14:59 PM »

I recently replaced a one wire oil pressure switch on my 1992 M25XP with the Kubota equivalent - part number 15841-39010.  I got it on Ebay for $15.

I got the part number from the Kubota parts manual on this site.  While replacing it did not cure my low oil pressure alarm issue, the Kubota part fit perfectly.  I had to use a deep socket and also had to drain the cooling system and remove a hose in order to get at the switch.   I tested the old switch and found it closed when the pressure dropped below around 10 psig, which was actually correct.

In my case, the low oil pressure was actually due to a bad oil pressure relief (or regulator) valve, which is located just below the oil filter.
Since you have an oil pressure gauge and the pressure reads correctly, it would seem your issue is caused by the switch or something else in the alarm circuit.

Roland Gendreau
1992 MK 1.5
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Bristol, RI

Ron Hill

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Re: Oil Pressure Alarm
« Reply #4 on: June 28, 2016, 02:47:10 PM »

kwalt : if you have the factory alarm that came with the engine it is a two wire alarm switch just like the M35 BC engine in the C34 MK II.

I'd first take Jim's advice and check/clean your connections that are at the switch.  You just might need a new switch?

A thought   
Ron, Apache #788
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