Yanmar oil pressure sender

[Donald Watson]

Ryan,

The sending unit of the vintage Yanmar genset probably follows an SAE
standard. Leroy's suggestion of the Teleflex site ww2.tflx.com was a good
one. The sending unit is a variable resistive device with a linear output
between approximately 240 and 33 ohms. With 0 lbs, the resistance should be
around 240 ohms. You can check this with an ohmmeter (providing you
disconnect the sending unit output wire) and reference to the body of the
sending unit and/or engine ground if it has single wire output, if there are
two output wires, you want to put the meter across both terminals. If the
sending unit ever saw 100 lbs, the resistance should lower close to 33 ohms,
half of that pressure (50 lbs) should produce a resistance close to 100
ohms.

If you want to check the gauge, you could disconnect the wire from the
sender on the gauge 'S' terminal, insert a temporary wire from the now
disconnected sending unit to the gauge, turn the ignition key on and ground
the sending unit. The gauge should read close to "0".

IF you purchased the small ¼ watt resistor pack from Radio Shack for close
to $6 or $7 dollars you could check the gauge by placing a resistor from the
'S' terminal of the gauge to ground.

Full Scale Reading = 240 ohms (two 470 ohm resistors twisted in parallel
will give you 235 ohms

Medium Scale = approximately 100 ohms

0 reading = 33 ohms (a 47 ohm resistor is close, the gauge should almost
read '0'

If there is a question about wiring, you can leave the sending unit in
place, remove the sending unit wire from the 'S' terminal on the oil
pressure gauge and read the resistance to ground with an ohm meter. You
should see something close to 240 ohms with the generator turned off.

Theoretically, you should be able to short the gauge output 'S' terminal and
see the gauge peg. WARNING! I did this recently, shorting the water temp
sending unit wire temporarily to make sure I was hooking up the correct
wire. The gauge pegged and stayed pegged. I've never had that happen. I
didn't realize that would be hazardous to the meter movement. There's
always something to learn.

Donn
76 FC33
South Kingstown, RI


From: WanderlodgeForum@yahoogroups.com
[mailto:WanderlodgeForum@yahoogroups.com] On Behalf Of Ryan Wright
Sent: Wednesday, May 07, 2008 9:39 PM
To: wanderlodgeforum
Subject: [WanderlodgeForum] Yanmar oil pressure sender

Does anyone have a NAPA (or otherwise) part number or cross reference
for the Yanmar generator oil pressure sending unit? My oil pressure
sender appears to be shot. Gauge runs all the way to the right
(highest possible pressure reading and then some) when operating.

Also, should the gauge go back to 0 when the sending unit is
disconnected? It doesn't. It does drop to between 60 and 90psi when I
press the "stop" button to warm up the glow plugs, but goes right back
to the top as soon as I hit "start". In fact, disconnecting the
sending unit doesn't seem to have any effect whatsoever on the gauge.

Just in case I replace the sending unit and that doesn't solve it, any
other ideas would be appreciated.

Thank you!

-Ryan