Oil Pressure Mystery Solved

[bsfree]

The oil pressure on my Perkins 108 has read 80psi since the day I bought the boat, a Challenger 32, I figured a constricted oil way so have changed the oil about 5 times and used a sludge remover each time. I had recently made a new instrument panel and installed all new gauges, senders and wiring. Everything was fine except for the oil pressure being so high, then I had a problem with the temperature needle not moving from 180. All the instruments were Teleflex, bought from Defender, so I emailed Teleflex tech support and started a dialogue with Joe. He was very helpful and told me how to test the gauge, which I did, but in the process I noticed the oil pressure gauge read 40psi without the engine running (I don't use a key switch, an oil pressure switch turns on the juice to the instruments). I mentioned this to Joe and he had me check the oil sender ohms, turns out I'd mistakenly ordered a two station sender instead of a single. The strange thing is that the PO (a group of 3-4 people co-owned the boat for a few years) must have made the same mistake, I have the original log book and read an entry that noted high oil pressure, but no mention of changing the sender. Anyway, I posted this, for what it's worth, as an experience that may save someone else a fair bit of frustration. Incidently, remove the signal wire before you test the ohms of a sender.
All the best

[Valiente]

So you were reading 40 PSI...twice?

Is the running pressure now 40 PSI in reality? I would have thought 50-55 PSI would be ideal, but I have a similarly sized Westerbeke, not a Perkins.

Interesting detective work, though.

[bsfree]

So you were reading 40 PSI...twice?

Kind of, as the gauge read 40psi before starting the engine, and then plus whatever the real pressure, came out to around 80psi. I only checked the ohms last night, so am looking forward to installing the correct sender this weekend and finally seeing my true oil pressure. Perkins states 30-60psi as normal, so I'll be happy with anything within that range.
Yes, the detective work was more by accident than design, but I guess all roads lead to Rome, this time at least.

[hellosailor]

I guess Teleflex's "two station sender" is one sender, with the internal resistance changed so it supplies enough power for two guages, rather than being two separate senders in one housing, which would be more expensive but more robust. (Fully redundant.)

Typical guages are just voltmeters, the senders are just variable resistors, whether it is oil or water or temperature or pressure, the guts all work on the same principle. Very clever--but kinda scary--to hear how Teleflex found an inexpensive way to support a "repeater" gauge.

[bsfree]

You guys understand the electronic in's and out's far more than I do, I was just happy to see resistance of 120 ohm's on the present sender, which is correct for two stations. Joe had told me that, and that 240 ohm's resistance is what I should see for a single station.

[Rockter]

I use an old-fashioned Burdon guage, and the oil pressure warning switch in case a line ruptures.

Works well, and cost about £20.