oil pressure sensor quandry

[patfarrell1949]

My 50CC has a Yanmar 4JH4-HTE with Teleflex i5501 engine monitoring. After erratic oil pressure readings (0 to 80 psi at steady 2300 rpm) I replaced the sensor with an Yanmar OEM part. Now I read zero pressure all the time! I can see no part number on the old sensor and a second new Yanmar sensor didn't improve things. I found some Teleflex info that indicates 0 psi should result from the highest resistance (240 ohms) and full gauge reading at lowest resistance (33 ohms). The Yanmar part reads 33 ohms at zero oil pressure which would seem to say it won't properly function with the Teleflex system.
Has anyone had to deal with this issue or know what the correct part number is?
Does anyone have any documentation for the Teleflex i5501 monitoring gear?

 

[Rich Stidger]

Easy to troubleshoot. At the sensor disconnect the wires, power up and look at the gauge. It should read zero. Now short the two sensor wires together and look at the gauge again. It should now read full scale. If the gauge performs as described, you have a USA standard gauge.
Now with the engine off measure the resistance of the oil pressure sender without any wires connected to it. It should read about 240 ohms. If it does,then the sender and the gauge are compatible and are both the USA system. If the gauge reads zero all the time you have an open connection in the wiring to the sender.
With the engine running the oil pressure sender should read some value more than 33 ohms and less than 240 ohms.
If the oil pressure sender reads 33 ohms without the engine running, then you have an European style sender and it is not compatible with your gauge.

See the attached files for more info.

 

[patfarrell1949]

Rich - thanks for the really helpful input. I've researched further and found that the Yanmar "standard" part is spec'd at 10 to 85 ohms. The new Yanmar sensor reads 10 ohms disconnected however my old sensor is reading 85 ohms disconnected. I found Yanmar has a second sensor rated at 85 to 10 ohms and this would align with your comment that a US version would read high resistance at zero psi.
Now all I have to do is find the part here in Puerto Rico!!
Thanks again...Pat

 

[jssailem]

Pat
To sources that may help.

1. SBO Shop. Contact @Dave Groshong
2. Fisheries Supply. If they can send parts to Alaska they can likely find a way to get it to Puerto Rico Marine & Boat Supplies Since 1928 | Fisheries Supply

 

[SEMPERAVANTI41]

I think the threads on the sensor are all 1/8" NPT. Any auto parts shop should have either American or European ohm output in stock. Bring the old sensor with you and you could match the threads.

 

[Charles Erwin]

I think the threads on the sensor are all 1/8" NPT. Any auto parts shop should have either American or European ohm output in stock. Bring the old sensor with you and you could match the threads.

The sender port on the motor side are BSPT (T=tapered) 28 threads per inch. - not NPT 27 threads. Get an adaptor like this -- Amazon.com: GlowShift 1/8 BSPT Male to 1/8-27 NPT Female Gauge Sensor Sender Thread Adapter Reducer : Automotive. Obviously verify the ports size - motor block and sender - before you order the adapter.

Anyway - the motor side port is probably tapped into aluminum. So tighten just enough (and no more) for a no leak seal. The central point is don't try NPT direct without an adapter. Otherwise you can crack the aluminum casting when you try to fix the leak that is being caused by these mismatched treads. Likely repairable but very inconvenient and pretty costly to fix.

Charles