Oil pressure going lower

[graham.hilder@domain.elided (Graham Hilder)]

Re Eric's pressure gauge readings gradually falling, Fred wrote:=20
>  Just change the oil pressure sender because oil has
>  undoubtedly gone past the seal and into the resistor board. =20

Well there's no doubt that those *^%#* awful sender units which Alfa uses =
do deteriorate over time, and that changing to a new unit as Fred says =
will usually restore your gauge readings.  But I have to quibble with =
Fred's explanation. I've opened up a good few discarded low-reading units =
over the years, to try and find out why they've deteriorated, and although =
I haven't found the answer, I'm sure it's not for Fred's reason (well, not =
in any of my samples anyway).  The ones I've opened up have all been clean =
and dry inside on the resistor board, and the rheostat wiper contact has =
been making good connection too.  All the mechanism (pivots etc) has been =
clean and freely-moving.  In other words, I coud never see a single thing =
wrong (or even suspicious) with any of these units!  I'm stumped.=20

The only thing I can think of is that the metal pressure-diaphragm =
work-hardens over time, with the continual flexing, and hence the =
diaphragm deflection gradually decreases (diaphgram becomes too stiff).   =
However I'm a metallurgical moron, so I've no idea if this is a sensible =
theory or not.=20

Oh, and one other suggestion re Fred's posting..... even if oil HAS leaked =
into the resistor-chamber, I don't think it would make any difference =
unless it's bad enough to have softened or dissolved the board and let the =
rheostat windings become unwound and messed up.  I'd guess that oil just =
lying around on a rheostat like this one isn't going to affect anything....=
. oil's a good enough insulator to be ineffective in this sort of low =
resistance circuit, probably even if it's dirty old oil full of metal =
filings.  In any case, even if the oil didn't  insulate too well, the =
gauge readings would be too high rather than too low. Well, so I reckon, =
anyway.=20

Whatever it is that causes these low readings, I'd sure like to know, so I =
can refurbish or recalibrate some of the discarded senders I have sitting =
around.  New senders are very expensive and don't last long anyway.  And I =
haven't found an alternative to the expensive genuine Alfa part.

Regards,
Graham H,
New Zealand.
(Alfasud x 3, GTV, Alfetta....  all with low press readings except those =
treated to new senders)

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