Oil Pressure read-out mystery

[Michael]

For a week or so after installation, an oil pressure gauge aboard Hali consistently indicated engine oil pressure of about 25 pounds per square inch at cruising RPM, and somewhat lower at idle.  During this time, the dual prong oil pressure switch (which feeds low oil pressure information to the instrument panel's low oil pressure idiot light and low oil pressure audible alarm) was disconnected from the audible alarm, becaused one of the two prongs was broken and, to prevent the alarm from sounding continuously, I disconnected its switched power feed in the instrument panel.

On installing a new oil pressure switch and reconnecting the audible alarm, the oil pressure gauge began reading 50 psi consistently at virtually all RPM settings (except zero RPM of course, at which the gauge correctly indicated no oil pressure) and the audible alarm did not sound when it should at startup.

There is discussion elsewhere on this board about the audible low oil pressure alarm not working (http://c34.org/bbs/index.php/topic,783.0.html), and I will chase down that problem separately. (I only mention it here as potentially relevant information regarding the pressure readout issue and not as a request for help.)

The fact that the oil pressure readout doubled makes me suspect a doubled voltage in the oil pressure send-oil pressure gauge system.  I suppose I could reverse the recent changes and check with a voltmeter but...

According to the Universal Service Manual (page 44) "during normal operation, the oil pressure will range between 40 and 60 psi"...so the current oil pressure readings do not make me unhappy but they are a bit suspect.

It seems to me likely that we have some Teflon tape (from the old oil pressure switch threads) in the engine oil and perhaps in the relatively narrow channels for oil at the bracket where the ports are for the oil pressure switch and oil pressure sender unit.

Other than has hinted at here, I have come up with no thoughts as to why the oil pressure readout has doubled (or, put another way, why it was not doubled earlier).  Any thoughts would be welcome.  (Some background to this post also appears in http://c34.org/bbs/index.php/topic,4477.0.html.)

[Ron Hill]

Mike : It would seem to me that the Teflon tape could be the culprit on the old switch (1/2 the normal reading pressure? - so it gave a low abnormal reading?).  I believe that most switches/senders have a tapered thread, just so you don't need any sealant and get metal to metal contact. 
You should not put anything on the threads of the temp sender, oil sender/switch or your zinc in the heat X.  All these items need a GOOD ground (-) contact. 

[Stu Jackson]

Michael, given what you've said, have you considered that the OLD one was reading half of what it should be reading?  If the manual says it should be reading between 40 and 60 and it reads 50, it could well be that there is no problem(?).

[Michael]

Thank you, Ron and Stu.

Yes, Stu, I agree the current oil pressure read-out is where we want it to be.  I'm just a little unsure that the gauge is reading accurately given its "half output" before.

Ron, I was using teflon tape willy-nilly, but did sometimes wonder where it went as there rarely seemed to be much left on the threads.